Objective
This Design Guide provides the information and resources necessary to design and install
cross-linked polyethylene (PEX) water supply systems in residential buildings. It includes
comprehensive design concepts and installation guidelines to increase the acceptance and
proper use of PEX. This document is targeted to meet the needs of home builders, designers,
and trade contractors. Its purpose is to introduce potential users to PEX and to enable
current users to optimize their PEX plumbing and minimize system costs. In addition, it will
allow code inspectors and homeowners to become familiar with the applications, performance
characteristics, and benefits of PEX water supply systems.

Background
Cross-linked polyethylene (PEX) is a high-temperature, flexible, polymer pipe. Cross-linking
technology was first developed in Europe and has since come into use around the world for
a variety of applications. PEX has a 30-year history of successful use in the European market
with extensive testing for durability and material performance. It was first introduced in North
America in 1984 where it has been primarily used for radiant floor heating, and more recently,
for domestic water distribution systems. It is approved for potable hot and cold water supply
systems as well as hydronic heating systems in all model plumbing and mechanical codes across
the United States and Canada.
The comparison of PEX to polybutylene piping (PB) appears to be a major obstacle to
mainstream acceptance by some code officials, trade contractors, and homeowners. But not all
plastics are the same, just as not all metals are the same. Polymer fittings for PEX pipe are far
more robust and reliable than those used for PB. A result of modern polymer technology, PEX
piping performs in ways that provide superior reliability, durability, and safety. Also, current
testing requirements for PEX are much more stringent than when PB piping was accepted and
installed in housing.
The PEX piping industry is highly regulated. Standards, specifications, and code requirements
define tight material and production quality controls. Continuous-use temperature ratings
as high as 200ºF (93ºC) are required as well as standardized chlorine resistance testing to
ensure that the piping will withstand the most aggressive drinking water conditions. Nationally
accredited, third-party certification agencies require strenuous quality control testing, including
random plant inspections and annual monitoring testing.
There are numerous opportunities for more widespread use of PEX pipe in the U.S. residential
market. The development of manifolds and parallel plumbing systems for flexible piping has
helped to advance its use. All major residential building codes permit the use of PEX piping,
but obstacles to its acceptance still remain. There is anecdotal and research information that
shows:

• Some plumbers are reluctant to use PEX piping due to a lack of experience with installation
methods and design requirements
• Some jurisdictions prohibit the use of PEX piping for water supply plumbing even though
PEX pipe is approved for use in all model codes
• Codes were originally written for rigid trunk and branch systems; while they have now been
amended to include PEX piping systems, they do not provide many system design details
• There is a perception among some that PEX piping systems are inferior as a building
product, generally based on knowledge of past failures of PB piping systems.
Although these hurdles exist, the following are among the many benefits of PEX piping systems.
• Ease of Installation – PEX pipe uses mechanical connections eliminating the need for
solders, flames, and chemicals. Its flexible nature allows it to bend around obstructions. Use
of manifolds can speed installation and improve performance.
• Corrosion Resistance – PEX piping will not pit or stress corrode.
• Scaling Resistance – PEX pipe’s smooth interior walls and chemical properties make it
resistant to mineral build-up.
• Cost Effectiveness – PEX plumbing systems are less labor intensive and can optimize
system performance.
• Availability of Pipe Sizes – PEX piping is available in a wide range of diameters.
• Energy Efficiency – PEX piping minimizes heat transmission through the pipe wall.
• Resistance to Freeze Damage – Under most circumstances, water in the pipe can be
frozen and thawed without damaging the pipe.
• Water Conservation – Well designed PEX plumbing systems can reduce the wait time for
hot water to reach the fixture.
• Environmentally Sound – PEX is an inert material and does not contain volatile organic
compounds (VOCs).
• Certification – PEX pipes and fittings must meet strict performance requirements.

Chapter 1 –
Although general research on hot water systems has been performed on various aspects of
plumbing systems, a recent literature search by the NAHB Research Center indicated that
specific system design information for flexible water supply plumbing is sparse. Documents
relied more on “standard practice” than on engineered or designed systems. Using these
approaches often leads to system designs that either supply more water than is needed at the
fixture, or do not take advantage of the characteristics of a flexible plumbing system to reduce
cost and improve performance.
This Design Guide provides the information and resources necessary to design and install
efficient and cost-effective PEX water supply systems in residential buildings. It illustrates
various plumbing configurations for a variety of house types as well as installation guidelines for
each method. Properly designed and installed PEX piping systems are beneficial for plumbing
designers, installers, and homeowners.

Applications
PEX piping can be used in a wide variety of applications in residential construction. This Design
Guide is focused on the design and installation of PEX hot and cold water supply systems,
which can be used for both new construction and remodeling projects.
Other applications for PEX are described in a separate section of this guide and include:
• Radiant floor heating systems for suspended floor systems or in slab construction
• Municipal water service pipe in underground applications
• Snow and ice melt systems for sidewalks, driveways, entrances, and ramps
• Turf conditioning for greenhouses, golf courses, and sports field surfaces
• Fire suppression systems (residential fire sprinklers)
Available in sizes from 1/4 to 2 inches, PEX piping can generally be installed in place of rigid
piping on a size-for-size basis. Home-run installations with central manifolds can be used to
balance pressures at the outlets and minimize hot water delivery wait time, reducing wasted
water and energy. Manifolds can be installed that reduce the amount of piping and fittings,
speed-up installation, and balance pressures throughout the system.

How to Use the Design Guide
This PEX Design Guide can be used by anyone considering the installation of PEX piping
for a residential plumbing system. It can be used by the novice as an introduction to PEX
piping or by the experienced plumber to optimize his/her approach. Building code officials
can use this Guide as a consolidated source of information on the application of PEX piping
in residential buildings. Builders can use this guide to learn about the advantages, installation
issues, and expected performance of PEX plumbing systems for discussions with sales staff and
homeowners.
Each section of this guide focuses on various aspects of using PEX piping.

• Chapter 1 – Introduction: Background information to educate the user about the history
and uses of PEX piping
• Chapter 2 – Advantages: Various advantages to using PEX piping in residential buildings
• Chapter 3 – Material Properties: Unique properties of PEX piping
• Chapter 4 – Joining Methods: Explanations of the various types of fittings and their
joining methods
• Chapter 5 – Types of PEX Plumbing Systems: Descriptions of the three types of PEX
piping system designs
• Chapter 6 – Code Acceptance: Information on major plumbing codes and relevant
jurisdictional code provisions for PEX piping
• Chapter 7 – Design: Designs and performance details of the three basic plumbing layouts
for four common house configurations to assist in evaluating which system provides the best
balance of performance, ease of installation, and cost for a particular house
• Chapter 8 – Lab Testing and Performance Data: System performance comparison of
three plumbing systems
• Chapter 9 – Installation: Detailed instructions for installing PEX piping
• Chapter 10 – Testimonials: Quotes from plumbers and home builders on their
experiences with PEX piping
• Chapter 11 – Other Applications: Other uses of PEX piping

• Appendix A: Additional lab testing data
• Appendix B: New Installation Checklist to aid plumbers with the process of installing PEX
piping
• Appendix C: Resources for additional information beyond this Design Guide
• Glossary: List of terms and acronyms used in this Design Guide
There are three main ways to use this guide:
• Introductory Overview: The guide can be read in its entirety as an introduction for those
who have little or no exposure to PEX piping.
• Planning Tool: The Code Acceptance and Design chapters, in particular, can be used to
optimize system designs and building layouts during the planning stage while the home design
is being finalized.
• Reference Guide: Certain sections can be extracted and read as needed. For example,
plumbers may want to reference the Installation section, or building inspectors may want to
reference the Code Acceptance section.

Ease of Installation
The installation of PEX pipe is generally easier than rigid pipe. It is available in long coils which
eliminates the need for coupling joints. Its flexible nature allows it to be bent gently around
obstructions, minimizing the use of fittings. No solvent, chemical, or solder joining is required.
The mechanical fittings are secure and reliable when installed properly. The pipe is lightweight,
making it safe to transport and easy to handle. For a comparison of the installation of rigid
metal pipe to PEX pipe.

 
Durability
Based on extensive testing and material performance over the span of more than 30 years,
PEX piping has proven to be a durable material that does not suffer from some of the historical
problems associated with metallic piping, such as reduced interior dimension, corrosion,
electrolysis, filming, mineral build-up, and water velocity wear. PEX piping will typically expand
if the system is allowed to freeze, and return to its original size when the water thaws.

Cost Effectiveness
PEX plumbing systems have lower installation costs than rigid metallic plumbing systems.
Installation time and labor required is greatly reduced. In service, the use of PEX systems can
reduce energy and water use by delivering water to the fixtures faster and by reducing losses in
the piping.
Energy Efficiency
PEX piping offers reduced heat loss and improved thermal characteristics when compared to
metallic pipe. In addition, less energy is used by the water heater because of shorter delivery
time for hot water with PEX parallel plumbing systems.2
1 The full PATH Field Evaluation report is available at http://www.toolbase.org.
2 Evaluation of Hot Water Distribution Systems by Numeric Simulation, 2004.
Building Technology Center, Oak Ridge National Laboratory.

Chapter 2
Noise Reduction
When properly secured, PEX piping can be significantly quieter than rigid systems. It is
inherently less noisy due to its flexibility and ability to absorb pressure surges.

Water Conservation
Properly designed PEX plumbing systems have the potential to conserve water. The flexibility of PEX allows it to bend around corners and run continuously, reducing
the need for fittings; this allows downsizing the pipe diameter to 3/8-inch for certain fixtures.
Home-run systems and 3/8-inch pipes minimize the time it takes hot water to reach the
fixture. Lengthy delivery time for hot water represents a significant waste of water as well as
energy; a problem exacerbated in larger homes.
In 2002, the NAHB Research Center conducted software simulations and laboratory tests on
a “typical” hot water system using a trunk and branch rigid pipe design and one that included a
3/8-inch diameter PEX home-run system. Results indicated that systems using shorter 3/8-inch
runs with a home-run manifold reduced the wait time for hot water and wasted less water than
longer runs of rigid pipe with many elbows and connections.

Environmentally Sound
PEX is a modification or enhancement of high-density polyethylene, an economical and highly
cost-effective construction piping material. Generally, manufacturing equivalent lengths of
plastic pipe consumes far less energy than manufacturing metallic pipe. The lighter weight of
PEX compared to metallic piping helps to lower transportation costs and energy consumption,
offering even greater benefit.
PEX pipes can be recycled as an inert filler material that can be incorporated into other
polymers for specific applications. There is also reduced water use through faster delivery time.
In addition, PEX pipe does not contain harmful VOCs.
PEX is a material made up of molecules of high-density polyethylene (HDPE) that are
permanently linked to each other by a process called crosslinking. Crosslinking makes PEX a
“thermoset” polymer, which gives it long-term stability.
Polyethylene can be crosslinked using several technologies. All methods induce links between
the single strands of PE to form a dense network through radical reactions. The number
of links between the strands determines the crosslink density and is an important factor in
determining the physical properties of the material. The minimum percent crosslinking for
each method is specified in the ASTM F 876 standard. The three most common methods of
crosslinking polyethylene are as follows:

Peroxide – Peroxides are heat-activated chemicals that generate free radicals for
crosslinking. This is called the Engel Process.
Moisture-cured Vinylsilane – This method involves grafting a reactive silane
molecule to the backbone of the polyethylene. This is called the Silane Process.
Beta Irradiation – This method involves subjecting a dose of high-energy electrons
to the PE. This is called the Radiation Process.
In European standards these three methods are referred to as PEX-A, PEX-B, and PEX-C,
respectively, and are not related to any type of rating system.
characteristics, all three methods have been utilized to manufacture approved PEX products.
As required in any manufacturing process, procedures for each technology must be established
and followed with good quality control checks in place to produce quality products.

Chapter 3 –
Temperature and Pressure
PEX piping meets all requirements for pressure and temperature performance in residential
applications. Consensus standards published by the American Society for Testing and Materials
(ASTM) International specify temperature and pressure-resistant capabilities of PEX pipe and
all tubing used in residential applications bears the appropriate test marking.
In the event of a water heating system malfunction, PEX piping is designed to accommodate
short-term conditions of 48 hours at 210ºF (99ºC) and 150 psi (1034 kPa) until repairs can
be made. The most commonly used safety relief valve (T&P) activates (opens) at either of
these temperature or pressure conditions. All PEX piping has been tested to withstand T&P
activation for 30 days to ensure that safety requirements are met. As such, PEX systems DO
NOT require the use of a special T&P valve.
ASTM F 876: Standard Specification for Cross-Linked Polyethylene (PEX) Tubing covers
PEX piping that is outside diameter controlled, and pressure rated for water at three
temperatures—160 psi @ 73.4ºF, 100 psi @ 180ºF, and 80 psi @ 200ºF. Included are
requirements and test methods for material, workmanship, dimensions, hydrostatic sustained
pressure strength, burst pressure, oxidative (chlorine) resistance, and environmental stress
cracking.
ASTM F 877: Standard Specification for Cross-Linked Polyethylene (PEX) Plastic Hot- and ColdWater Distribution Systems covers requirements and test methods for PEX hot- and cold-water
distribution system components made in one standard dimension ratio, and intended for 100
psi water service, up to and including a maximum working temperature of 180ºF. Components
are comprised of piping and fittings. Requirements and test methods are included for
hydrostatic sustained pressure strength, thermocycling resistance, fittings, and bend strength.

Flexibility
The flexible nature of PEX allows it to be bent gently around obstructions and installed as one
continuous run without fittings. Slight changes in direction are made easily by bending the pipe
by hand. There is a predetermined bend radius of a 90-degree change of direction without
installing a fitting (reference manufacturer’s installation instructions). Minimizing mechanical
connections can result in quicker installations, less potential for leaks at fittings, and less
resistance due to pressure drops through fittings.

Noise and Water Hammer Resistance
As water flows through pipes, pressure in the system gives moving water energy, known as
kinetic energy. Kinetic energy increases with the speed of water and also with the mass of
water that is flowing. When the flow of water is stopped, such as when a valve or faucet is
closed, this kinetic energy must be dissipated in the system.
The ability of a plumbing pipe to dissipate energy due to surge in water pressure is based
on the pipe’s modulus of elasticity, a measure of material stiffness. A higher modulus of
elasticity means the material is more rigid. Copper pipe is 180 times more rigid than PEX pipe.
Ultimately, this means that with rigid piping systems, pressure surges can produce noticeable
banging sounds as energy is dissipated, thus causing what is known as “water hammer.” The
pressure surge that causes water hammer can produce instantaneous pressures of 300 to 400
psi (2070 to 2760 kPa), which can cause damage to rigid pipes, fittings, and connections.
The flexibility of PEX pipe allows the pipe itself to absorb energy from pressure surges and
eliminate or reduce the occurrence of water hammer.

Resistance to Freeze Damage
PEX pipes are less susceptible to the effects of cold temperatures retaining their flexibility even
below freezing. This flexibility means that if water-filled PEX piping freezes, the elasticity of the
material allows it to expand without cracking or splitting, and then to return to its original size
upon thawing. This applies when PEX pipes have room to expand evenly along their length, as is
typical when installed within walls or ceilings. PEX pipes inside a slab may not be able to expand
evenly.

Chlorine Resistance
The U.S. Environmental Protection Agency (EPA) recommends that all drinking water be
disinfected, typically using free chlorine, chloramines, or other less common methods.
Currently, the majority of potable drinking water in the United States and Canada is disinfected
using free chlorine. For water treated with free chlorine, the EPA sets a maximum disinfectant
level of 4.0 parts per million (ppm) within the water distribution system.
The second-most common disinfectant is chloramines. Research conducted by Jana
Laboratories, at the request of the Plastics Pipe Institute (PPI), indicates that free chlorine is
generally more aggressive to cross-linked polyethylene (PEX) pipes than chloramines.
To ensure the reliability of PEX piping systems in hot chlorinated water applications, it is a
requirement of the PEX pipe product standard specification ASTM F 876 that all PEX pipes
intended for use with potable water have a minimum extrapolated lifetime of 50 years when
tested in accordance with test method ASTM F 2023: “Standard Test Method for Evaluating the
Oxidative Resistance of Cross-linked Polyethylene (PEX) Tubing and Systems to Hot Chlorinated
Water.” The minimum requirement applies to traditional domestic applications.4
The test conditions of ASTM F 2023 require that the test fluid has a minimum oxidative
reduction potential (ORP) of 825 mV. To produce test fluid with this high ORP, third-party test
laboratories typically use reverse osmosis-purified water with a free chlorine concentration
of 4.3 +/- 0.3 ppm (4.3 mg/L) and pH of 6.8 +/- 0.2, resulting in an ORP of 825 mV or higher.
This represents a very aggressive water quality, which gives conservative results. This test
procedure is designed to extrapolate the life expectancy of a hot-water plumbing pipe when
used at a water temperature of 140°F and a pressure of 80 psi. Continuous recirculation and
traditional domestic4 conditions can both be evaluated by ASTM F 2023.
PEX pipe manufacturers must have pipes tested and certified by NSF International, UL and/or
other third-party certification agencies to meet the requirements of ASTM F 876, including
chlorine resistance. In addition, manufacturers may have pipes certified to NSF International
protocol P 171: “Chlorine Resistance of Plastic Piping Materials.” PEX piping systems use fittings
that also must comply with ASTM standards, and are made from brass, copper, or hightemperature engineered polymers that are chlorine-resistant.
In summary, PEX pipe has shown itself to be resistant to attack from chlorine and chloramines
under a wide range of conditions, and has performed reliably in all regions of North America.

Corrosion Resistance
PEX pipe and fittings have been tested extensively with aggressive potable water conditions and
did not pit or corrode. PEX pipe and fittings are tested with corrosive pH levels between 6.5
and 6.7, much lower and more aggressive than levels found in common water systems.
A related aspect of corrosion in pipes is concerned with flow erosion. Flow erosion tests of
PEX fittings were conducted by the PPI High Temperature Division (HTD). See “Erosion Study
on Brass Insert Fittings Used in PEX Piping Systems,” PPI-TN-26 for discussion and results.

Ultraviolet (UV) Resistance
Like most plastics, the long-term performance of PEX will be affected by UV radiation from
sunlight. Although most PEX pipes have some UV resistance, PEX pipes should not be stored
outdoors where they are exposed to the sun. Precautions must be taken once the pipe is
removed from the original container. Each PEX pipe manufacturer publishes a maximum
recommended UV exposure limit, based on the UV resistance of that pipe. Do not allow PEX
pipes to be over-exposed beyond these limits. PEX pipes should not be installed outdoors,
unless they are buried in earth or properly protected from UV exposure, either direct or
indirect.
Indirect (diffused) and reflected sunlight also have UV energy. If PEX will be exposed to
sunlight continuously after installation, such as in an unfinished basement, cover the pipe with
a UV-blocking sleeve (black preferred) or approved pipe insulation. Different manufacturers’
pipes have different degrees of UV resistance as indicated on their labels; always follow the
recommendations provided by the particular manufacturer.
See PPI “UV Labeling Guidelines for PEX Pipes,” TN-32.

Caution
• Do not store PEX pipes outdoors.
• Keep PEX pipes in original packaging
until time of installation.
• Ensure that exposure to sunlight
during installation does not exceed
the maximum recommended UV
exposure time as recommended by
the manufacturer.

Inert Material – Safe for Drinking Water
Since PEX piping is used to transport potable water, it must comply with federal regulations
for public safety. PEX materials are inert (not chemically reactive) and cannot contaminate the
potable water passing through them. The fittings are mechanical and do not require the use of
solvents or chemicals that might leach into the water when the system is first used.
Testing and certification must comply with NSF/ANSI Standard 61: Drinking Water System
Components - Health Effects, and Standard 14: Plastic Pipe System Components and Related
Materials. The primary focus of Standard 61 is to establish minimum health effect requirements
for chemical contaminants and impurities that are indirectly imparted into drinking water
from products, components, and materials used in potable water systems. PEX piping systems
are tested at water pH levels from 5.0 to 10.0, both excessive acidity and alkalinity, beyond
levels encountered in potable water systems. PEX pipe does not corrode, and it is resistant
to mineral build-up. NSF/ANSI Standard 14 covers physical, performance, and health effect
requirements for plastic piping system components used in potable hot- and cold-water
distribution systems.

PEX Piping Dimensions and Flow Characteristics

Chapter 3 –Table 3.3 – Pressure Loss
PEX plumbing systems are recognized in all major building model codes and are commonly used
for hot- and cold-water distribution applications, water service lines, and radiant floor heating
systems. The following is a summary of relevant model code requirements which specifically
pertain to PEX and plastic pipe and fittings used for domestic water supply.
The user must determ ne wh ch codes are
app cab e to h her spec fic project, and a so
must ensure comp ance w th a l loca , state,
and federal codes, regu at ons, and standards.
Codes are constant y rev ewed and updated.
PEX water supp ng has been adopted in
the model codes s nce 1993.

International Residential Code (IRC-2003)
P2605 Support, P2605.1 General. Piping shall be supported at distances not to exceed
those indicated in Table 2605.1. For PEX, maximum horizontal support spacing is 32 inches, and
maximum vertical support spacing is 10 feet (mid-story guide for sizes 2 inches and smaller).
P2608.3 Plastic Pipe, Fittings, and Components. All plastic pipe, fittings, and
components shall be third-party certified as conforming to NSF 14.
P2903.8 Parallel Water-Distribution System Manifolds. Hot and cold parallel waterdistribution system manifolds with individual distribution lines to each fixture or fixture fitting
shall be sized and installed in accordance with Sections P2903.8.1 through P2903.8.7.
P2903.8.1 Sizing of Manifolds. Manifolds shall be sized in accordance with Table P2903.8.1.
A maximum gallon per minute (gpm) is specified for different nominal inside diameter sizes for
plastic and metallic manifolds.
P2903.8.3 Maximum Length. The maximum length of individual distribution lines shall be
60 feet (18.2 m) nominal.
P2903.8.5 Support and Protection. Plastic piping bundles shall be secured in accordance
with manufacturer’s installation instructions and supported in accordance Section P2605.
Bundles that have a change in direction equal to or greater than 45 degrees shall be protected
from chaffing at the point of contact with framing members by sleeving or wrapping.
P2904.5 Water Distribution Pipe. References Table P2904.5. PEX plastic tubing shall
conform to ASTM F 877 and CSA B137.5 standards.
P2904.9.1.4 Cross-linked Polyethylene Plastic (PEX). References Section P2904.9.1.4.1
or Section P2904.1.4.2.
P2904.9.1.4.2 Mechanical Joints. Mechanical joints shall be installed in accordance with
manufacturer’s instructions. Fittings for PEX plastic tubing as described in ASTM F 1807, ASTM
F 1960, ASTM F 2080, and ASTM F 2159, shall be installed in accordance with manufacturer’s
instructions.
P2904.16.2 Plastic Pipe or Tubing to Other Pipe Materials. Joints between different
grades of plastic pipe or between plastic pipe and other piping material shall be made with an
approved adapter fitting.

International Plumbing Code (IPC 2003)
605.3 Water Service Pipe. Water service pipe shall conform to NSF61 and shall conform to
one of the standards listed in Table 605.3 (ASTM F 876, ATM F 877, and CSA-B137.5).
605.4 Water Distribution Pipe. Water distribution pipe shall conform to NSF 61 and shall
conform to one of the standards listed in Table 605.4 (ASTM F 877, and CSA-B137.5).
605.5 Fittings. Pipe fittings shall be approved for installation with the piping material installed
and shall conform to one of the standards listed in Table 605.5 (ASTM F 1807, ASTM F 1960,
and ASTM F 2080).
605.17 Cross-linked Polyethylene Plastic. Joints between cross-linked polyethylene plastic
tubing or fittings shall comply with Sections 605.17.1 and 605.17.2.
605.17.3 Mechanical Joints. Mechanical joints shall be installed in accordance with
manufacturer’s instructions. Fittings for PEX tubing as described in ASTM F 1807, ASTM F
1960, and ASTM F 2080 shall be installed in accordance with manufacturer’s instructions
605.23.2 Plastic Pipe or Tubing to Other Piping Material. Joints between different
grades of plastic pipe or between plastic pipe and other piping material shall be made with an
approved adapter fitting.
Chapter 4 – CodE ACCEPTAnCE
National Standard Plumbing Code (NSPC 2003)
3.4.1. Plastic Piping. Plastic piping materials used for the conveyance of potable water shall
comply with NSF 14 and be marked accordingly.
3.4.2. Water Service Piping. Water service piping to the point of entrance into the building
shall be of materials listed in Table 3.4, and shall be water pressure rated for not less than 160
psig at 73°F. Table 3.4: PEX Plastic Water Distribution Systems (ASTM F 877 with ASTM F
1807, F 1960, or F 2098 Fittings)
3.4.3. Water Distribution Piping. Water piping for distribution of hot and cold water
within buildings shall be of materials listed in Table 3.4, and shall be water pressure rated for
not less than 100 psig at 180°F. Plastic piping used for hot water distribution shall be installed in
accordance with requirements of Section 10.15.8. NOTE: The working pressure rating for certain
approved plastic piping materials varies depending on pipe size, pipe schedule, and methods of
joining.
10.15.8 Plastic Piping. Plastic piping used for hot-water distribution shall conform to the
requirements of Section 3.4 and Table 3.4. Piping shall be water pressure rated for not less
than 100 psi at 180°F. NOTE: The working pressure rating for certain approved plastic piping
materials varies depending on pipe size, pipe schedule, and methods of joining. Plastic pipe
or tube shall not be used downstream from instantaneous water heaters, immersion water
heaters or other heaters not having approved temperature safety devices. Piping within 6
inches of flue or vent connectors shall be approved metallic pipe or tube. Normal operating
pressure in water distribution piping systems utilizing approved plastic pipe or tube for hotwater distribution shall not be more than 80 psi.

Uniform Plumbing Code (UPC-2003)
604.11 PEX. Cross-linked polyethylene (PEX) tubing shall be marked with the appropriate
standard designation(s) (see Chapter 9) for which the tubing has been approved. PEX tubing
shall be installed in compliance with the provisions of this section.
604.11.1 PEX Fittings. Metal insert fittings, metal compression fittings, and cold expansion
fittings used with PEX tubing shall be manufactured to and marked in accordance with the
standards for the fittings (see Chapter 9).
604.11.2 Water Heater Connections. PEX shall not be installed within the first 18 inches
(457 mm) of piping connected to a water heater.

International Code Council (ICC)
Evaluation Service Reports (ESR) and Evaluation Reports (ER)
International Code Council-Evaluation Service (ICC-ES) conducts technical evaluations of
building products, components, methods, and materials. The evaluation process culminates
with issuance of technical reports that, because they directly address code compliance, are
useful to both regulatory agencies and building-product manufacturers. Agencies use evaluation
reports to determine code compliance and enforce building regulations; manufacturers use
reports as evidence that their products meet code requirements and warrant regulatory
approval. Several PEX manufacturers have ESRs or ERs.

International Association of Plumbing and Mechanical Officials
(IAPMO) Guide Criteria
The IAPMO Guide Criteria (IGC) procedure provides manufacturers and product developers
an opportunity to draft IAPMO standards as a vehicle for introducing new products, when
no applicable standard exists for the product. Once an IGC is accepted, IAPMO can list
products manufactured in compliance with the new requirements. Some PEX and PEX fitting
manufacturers have products listed under IGCs.

C904-06 American Waterworks Association (ANSI/AWWA
C904-06)
This standard describes PEX pressure pipe made from material having a standard PEX material
designation code of PEX 1006 in ASTM F 876 for use as underground water service lines in
sizes 1/2 inch through 3 inches, and conform to a standard dimension ration of SDR9.
Included in this standard are criteria for classifying PEX plastic pipe materials and a system of
nomenclature, requirements, and test methods for materials and pipe. Methods of marking are
given. Design, installation, and application considerations are discussed in the forward of this
standard.
There are several types of joining methods or fittings used with PEX plumbing systems. All are
mechanical fittings that are either directional or transitional. PEX piping cannot be joined by
solvent cementing.
Most PEX piping manufacturers have their own mechanical
fitting system. The method of connection should comply
with the manufacturer’s recommendations and instructions.
Fittings are regulated to comply with performance and
material criteria from recognized standards. They should
be marked by a certified third-party agency such as NSF,
IAPMO, CSA, IGC, UL or other third-party testing and listing
agency.
The most common types of fitting systems used are Cold Expansion Fittings and Metal or
Plastic Insert Fittings. Other types of fittings are available but are less common.
Chapter 5 – JoInInG METHodS
Cold Expansion Fittings with PEX Reinforced Rings
This type of fitting requires that the PEX piping, with a reinforcing PEX ring placed over the
end of the pipe, is expanded before the fitting is inserted into the pipe end. The expanded pipe
end is allowed to retract onto the fitting to form the seal—the “memory” of the pipe allows it
to tighten over the fitting. An expander tool is required to expand the pipe and the PEX ring
together. ASTM F 1960 is applicable to fittings that use a PEX reinforcing ring.

Cold Expansion Fittings with Metal Compression Sleeves
This type of fitting requires that the PEX piping is expanded before it is placed over the
oversized fitting. The pipe shrinks down over the fitting insert, then a metal compression
sleeve is pulled over the connection, compressing the pipe over the fitting. A tool is required
to expand the pipe and to pull the sleeve over
the pipe. ASTM F 2080 is applicable to cold
expansion fittings that use a metal compression
sleeve.

Metal or Plastic Insert Fittings
This type of fitting uses a metal crimp ring that is compressed around the PEX piping to secure
it to the fitting. The crimp ring can be copper or stainless steel. Fittings can be made of copper,
brass, bronze, or plastic. The fitting will typically have a barbed or ribbed annular end.
The PEX pipe slides over the barbed or ribbed annular section. Prior to making the connection,
the metal crimp ring is slid over the PEX piping and away from the end of the pipe. The piping is
pushed over the fitting, the crimp ring is slid down over that section and aligned over the fitting
ribs, and a tool is used to compress the crimp ring around the assembly.

Copper Crimp Ring
The copper ring is crimped equally around the fitting. The go-no-go gauge ensures a proper
crimp. Some manufacturers use o-rings on their metal fittings to make the seal with the pipe.
ASTM F 1807 is the applicable standard for metal insert fittings. ASTM F 2159 is the applicable
standard for plastic fittings. ASTM 2434
is the applicable standard for metal insert
fittings with o-rings.

Stainless Steel Clamp
The stainless steel ring is crimped using a ratcheting tool, which only releases once a proper
crimp is achieved. ASTM 2098 is the applicable standard for stainless steel insert rings.

Stainless Steel Sleeve
This type of fitting is made of metal and uses a press sleeve or cap to secure the PEX pipe to
the fitting. These fittings have ribbed annular ends that are inserted into the PEX pipe. A sleeve
or cap slides over the outer part of the piping and the fitting is inserted into the pipe. The pipe
must be fully inserted. A press tool is used to make the final connection. It is important that
the appropriate tool is used per manufacturer’s
instructions. This type of fitting is often used in
other industries to make pneumatic or hydraulic
hose line connections.

Push Type Fittings
This type of fitting uses an interlocking mechanism to connect the PEX pipe to the fitting.
The pipe is inserted, or pushed, into the fitting, and locked into place with a fastening device
that keeps the pipe from being backed-out or disconnected. This type of fitting is sometimes
referred to as a “quick connect” fitting. Push type fittings typically use some type of o-ring
or gasket to form a seal around the PEX
pipe. A support liner is inserted into
the pipe, and a fastening system with a
locking component, such as a snap ring
or twist collar, is used to ensure that
the connection remains permanent.
ASSE 1061 and IAPMO – IGC 188 are
the applicable standards for push type
fittings. Not all fittings of this type are
permitted to be installed in inaccessible
locations or underground. Verify with
your manufacturer and local codes before
installation.

Standard Specifications for Fittings
Fittings are categorized in accordance with ASTM or IAPMO specifications, as follows:
ASTM F 1807: Standard Specification for Metal Insert Fittings Utilizing a Copper
Crimp Ring for SDR9 Cross-Linked Polyethylene (PEX) Tubing
This specification covers metal insert fittings and copper crimp rings for use with PEX tubing
that meet requirements in ASTM F 876 and F 877. These fittings are intended for use in 100
psi (690 kPa) cold- and hot-water distribution systems operating at temperatures up to and
including 180ºF (82ºC). Requirements for materials, workmanship, dimensions, and markings to
be used on fittings and rings are also included. Size range is 3/8 to 1 1/4 inches.
ASTM F 1960: Standard Specification for Cold Expansion Fittings with PEX
Reinforcing Rings for Use with Cross-Linked Polyethylene (PEX) Tubing
This specification covers cold expansion fittings and PEX reinforcing rings for use with PEX
plastic tubing that meet requirements of ASTM F 876 and F 877. These fittings are intended for
use in 100 psi (690 kPa) cold- and hot-water distribution systems operating at temperatures
up to and including 180ºF (82ºC). The system is comprised of a PEX reinforcing ring and a
cold expansion fitting. Included are requirements for materials, workmanship, dimensions, and
markings to be used on fitting components. Size range is 3/8 to 1 1/2 inches.
ASTM F 2080: Standard Specification for Cold Expansion Fittings with Metal
Compression Sleeves for use with PEX Pipe
This specification covers cold-expansion fittings using metal compression sleeves for use with
PEX plastic pipe that meet requirements of ASTM F 876 and F 877, whereby the PEX pipe is
cold-expanded before fitting assembly. These cold expansion fittings and metal compression
sleeves are intended for use in residential and commercial, hot and cold, potable water
distribution systems, with continuous operation at pressures up to and including 100 psi (690
kPa), and at temperatures up to and including 180ºF (82ºC). Included in the specification are
requirements for materials, workmanship, dimensions, and markings to be used on fittings and
compression sleeves. Performance requirements are as referenced in ASTM F 877. Size range is
3/8 to 2 inches.
ASTM F 2098: Standard Specification for Stainless Steel Clamps for Securing SDR9
Cross-Linked Polyethylene (PEX) Tubing to Metal Insert Fittings
This specification covers stainless steel clamps for use with four sizes of insert fittings that
comply with F 1807, and cross-linked polyethylene (PEX) plastic tubing that complies with
F 876 or F 877. These clamps are intended as an alternative to the copper-alloy crimprings of Specifications F 1807 or F 2159 for use in 100 psi (689.5 kPa) cold- and hot-water
distribution systems operating at temperatures up to and including 180ºF (82ºC). Included
are requirements for materials, workmanship, dimensions, and marking of the stainless steel
clamps; requirements for deforming the clamps, which apply to assemblies of PEX tubing
and Specifications F 1807 and F 2159, insert fittings secured with deformed clamps per this
specification.
ASTM F 2159: Standard Specification for Plastic Insert Fittings Utilizing a Copper
Crimp Ring for SDR9 Cross-Linked Polyethylene (PEX) Tubing
This specification covers plastic insert fittings and copper crimp rings for use with PEX pipe
that meets requirements in ASTM F 876 and F 877. It establishes requirements for sulfone
plastic insert fittings and copper crimp rings for PEX plastic tubing. These fittings are intended
for use in 100 psi (690 kPa) cold- and hot-water distribution systems operating at temperatures
up to and including 180ºF (82ºC). Included are requirements for material, molded part
properties, performance, workmanship, dimensions, and markings to be used on fittings and
rings. Size range is 3/8 to 1 inch.
ASTM F 2434: Standard Specification for Metal Insert Fittings Utilizing a Copper
Crimp Ring for SDR9 PEX Tubing and SDR9 PEX-AL-PEX Tubing
This specification covers metal insert fittings with o-ring seals and copper crimp rings for use
with cross-linked polyethylene (PEX) tubing in 1/2, 3/4, 1, and 1 1/4 inch nominal diameters
that meet the requirements for Specifications F 876 and F 877. These fittings are intended for
use in 100 psi (689.5 kPa) cold- and hot-water distribution systems operating at temperatures
up to and including 180ºF (82ºC). Included are the requirements for materials, workmanship,
dimensions, performance, and markings to be used on the fittings and rings. Size range is 1/2 to
1 1/2 inches.

IAPMO – IGC 188: Removable and Non-Removable Push Fit Fittings
This specification covers removable and non-removable push fit fittings for use with PEX pipe
that meet requirements in ASTM F 876 and F 877. The purpose of this standard is to establish
a generally acceptable standard for fittings with a quick assembly push-fit mechanism that are
used with various types of outside diameter controlled tubing. The fittings range in size from
3/8 to 2 inches. This standard covers minimum requirements for materials of construction and
prescribes minimum performance requirements for fitting joints and marking and identification
requirements.

ASSE Standard – 1061
This standard applies to push-fit fittings that can be used with one or more of the following
materials:
1. PEX tubing complying with ASTM F 876 or ASTM F 877;
2. Type K, L and M copper tubing complying with ASTM B 88; and
3. CPVC tubing complying with ASTM D 2846.
Push-fit fittings may be designed to be used with one or more types of tubing that conform to
the dimensions as specified in their respective standard. This standard serves to supplement
ASTM F 877, ASTM D 2846 and ASTM B 88 in describing a test method for a specific type of
push-fit fitting system to be used with PEX, Copper, and/or CPVC tubing. This standard covers
minimum fitting joints, marking, and identification.
The unique properties of PEX piping allow it to be configured in a number of different
residential plumbing system designs. This section describes three layout options: trunk and
branch, home-run, and remote manifold. By carefully choosing the right system for the
application, the plumbing designer can produce a home that balances cost, installation time, and
performance.

Trunk and Branch
For decades, trunk and branch (T&B) piping systems have been used by plumbers for potable
water distribution using rigid plastic or metal pipe. Installation of PEX piping can be performed
in a similar manner using a main trunk line to supply various branch take-offs to specific outlets.
Typically the trunk line services numerous outlets while the branch line services generally one
to three closely grouped outlets, such as in a bathroom. Installation of PEX piping in the T&B
design follows the general design requirements established in plumbing codes.
As with rigid piping systems, use of tee and elbow fittings allows for the connection of branch
take-offs from the main trunk. However, given the fact that PEX is available in long coils, the
use of coupling fittings can be reduced or eliminated. Unlike rigid pipe systems, many elbow
fittings can be eliminated in favor of sweep turns of the piping.
Specific features and
advantages of the PEX trunk
and branch design include:
• Simple system design
conversion from rigid
piping to flexible PEX
piping
• Opportunities to reduce
the number of fittings
installed
• T&B systems will deliver
hot water quicker during
sequential flows
• T&B systems will generally
supply one fixture at a
higher pressure
Figure 6.1 – PEX Pipes in a Trunk and Branch System Design

Home-Run
The unique features of PEX piping make it ideal for use in manifold-type system designs,
commonly referred to as home-run plumbing systems. In this design, all fixtures are fed from
dedicated piping that runs directly and unbroken from central manifolds. The hot water
manifold should be located in close proximity to the hot water source to ensure fast and
efficient delivery.
All outlets are individually fed from a common manifold or two central manifolds (hot and
cold). Because inline fittings are eliminated, pressure losses along the line are reduced, allowing
the piping size to be reduced for certain fixtures. Three-eighths-inch piping may be used for
lower flow applications and 1/2-inch piping is recommended for higher flow applications.
The home-run system often has more evenly distributed pressure losses when flowing water
to fixtures since all lines are fed from a common point, rather than adding multiple fixtures into
the same pipe section. Smaller diameter pipe also results in quicker delivery of hot water from
the water heater, although each line must be purged independently.
If the manifold is installed using valved outlets, many plumbing codes do not require a second
valve at the fixture, speeding installation and adding convenience much like an electrical breaker
panel.
Specific features and
advantages of the PEX
home-run design include:
• Easier piping runs to
each fixture using smaller
diameter piping
• Opportunity to eliminate
all fittings between the
manifold and the outlet
• Opportunity to have
centrally located individual
shut-offs housed at the
manifold
• Quicker delivery of hot
and cold water to the
outlets
• A more stable pressure
to each fixture when
operating simultaneous
fixtures

Remote Manifold
A third method for installing PEX piping combines elements of the first two systems and is
typically referred to as a remote manifold system design. The basic approach to this system
is running hot and cold trunk lines to some convenient location in close proximity to multiple
fixtures, such as for a bathroom group. At this point a smaller remote manifold is installed on
each trunk line. The remote manifolds can be flow-through or closed end. Individual branch
lines are then run to each fixture in the same manner as the central manifold. Manifolds with
valves must be installed in accessible locations; manifolds without valves may be installed in
enclosed spaces.
The remote manifold system performs in a similar manner to the T&B system. However, it
simplifies the installation due to the reduced number of fittings that are required.
Specific features and
advantages of the PEX
remote manifold design
include:
• Relatively simple system
design conversion from
rigid piping to flexible PEX
piping
• Opportunities to reduce
the number of fittings
installed
• Quicker hot water
delivery during sequential
flows
• Opportunity to have
centrally located individual
shut-offs housed at the
remote manifold
The unique features of PEX piping allow for a great deal of system design freedom that can
increase the performance and savings associated with the plumbing system. In today’s highperformance homes, many designers recognize that the plumbing system can be designed to
provide hot or cold water faster with much less energy loss. PEX plumbing systems can be
designed to enhance these features but, like any plumbing system, PEX piping systems perform
best and cost less to install when planned during the home’s design phase. Advanced planning
allows maximum performance, while limiting the lengths of pipe and number of fittings used.
And, when considered early enough in the house planning stage, a few simple room layout
considerations can greatly improve the performance of the plumbing system. By consulting the
codes and local inspectors in advance, builders and plumbers can also avoid costly time delays
due to code issues arising during construction.
This chapter describes a process that provides the guidance and tools needed to successfully
layout a PEX piping system in nearly any home. Four major areas of the design process are
highlighted:
• Consult Local Codes
• Optimize Home Layout
• Select Piping System Type
• Plan Piping Routing, Manifold, and Valve Locations

Consult Local Codes
If PEX piping has not been used before, or is still uncommon in your local area, it is helpful to
review the local codes for use of PEX piping. As discussed in the Chapter 4 of this document,
PEX piping is approved for use in all model codes. Local amendments may restrict or change
the way PEX may be used for certain applications. For that reason, it is important to consult
local codes to determine specific requirements before beginning a new piping design.
It may also be helpful to consult with local building inspectors to notify them in advance
that you plan to use PEX piping for your project. They can be helpful in pointing out local
requirements and amendments. Alerting the inspector of your intent to use a new technology
in advance can help to avoid delays that often occur when an unfamiliar material is encountered
on the jobsite. This design manual may be useful as a reference guide for an inspector who is
unfamiliar with PEX.
In the event that questions arise regarding the application, performance, or code acceptance of
PEX, both the Plastics Pipe Institute (PPI) and the Plastic Pipe and Fittings Association (PPFA)
can provide support. Each organization can provide technical and training materials to aid code
officials and plumbers.

Optimize Home Designs
Ironically, some of the most substantial problems with modern plumbing system designs
relate not to the piping itself, but to the design and layout of the house. The materials that are
chosen for framing, the location of rooms, the location of the water heater(s), and the point
at which the water main enters the home all have a substantial impact on the performance of
a plumbing system. Often, the design of the plumbing system is left until the end of the design
process when the home layout is largely determined. This often results in a poorly performing
and excessively costly system. By observing a number of guidelines early in the home design
process, PEX piping can be installed in a way that minimizes costs, eases installation, and
increases homeowner satisfaction.
The key to optimizing home designs for PEX plumbing is to minimize pipe lengths from the
water main and water heater. While this may seem intuitive, it cannot be stressed enough.
Short piping runs result in shorter wait times for hot water, fewer fittings, faster installation
time, and lower material costs. This can be accomplished by the builder or designer in the early
planning stage using several basic design principles.

1. Group fixtures together – Grouping plumbing fixtures around a common location can
result in saving time, materials, hot water energy, and water. This can be done between
floors as well, such as in the case of stacked bathrooms. Where possible, avoid locating
bathrooms long distances from the water heater.
2. Centrally locate distribution point – Centrally located water heaters and incoming
water supplies can significantly improve the performance of a plumbing system. Often water
heaters are arbitrarily located for convenience or placed in the utility room as far from
the living space as possible. This approach often leads to exceedingly long plumbing runs
along with the resultant increase in materials, installation time, and water and energy use.
Whenever feasible, locate the water main and heater as close as possible to the mid-point of
the fixture groupings to keep piping runs short.
3. Create spaces for bundled pipe runs – Particularly applicable to home-run PEX
plumbing runs where few fittings are installed, simultaneous installation of multiple piping
runs will reduce installation time. The flexibility of PEX piping and the long, unbroken lengths
that can be easily spooled enable the simultaneous installation of multiple plumbing lines
running in the same direction using common holes and chases. By creating space in soffits
and chases for piping bundles, installation time can be reduced. However, cold and hot water
lines should be bundled separately.
4. Use building elements that ease piping installation – Using building elements such as
open web floor trusses in some locations can dramatically speed up the process of installing
plumbing piping. This can also speed up the process of installation of other mechanicals
including ducting and wiring.

Select Piping System Design
The next step for the designer, plumber, and builder is to select the most appropriate plumbing
system design for the home. The unique properties of PEX piping allow it to be configured in a
number of different designs. All have been shown to work well in residential applications, and
all are code approved. Depending on the design of the home, each has different performance
characteristics, installation costs, material costs, and ease of installation. The selection of a
system design is generally based on a combination of key factors such as material cost, labor
time, ease of installation, system performance, and installer preference.
The challenge for a plumbing designer is to select the system that balances the unique needs of
the installer, homeowner, and builder. The purpose of this chapter is to provide a comparison
of the three most prevalent PEX plumbing systems, trunk and branch, home-run, and remote
manifold, and the guidance to select between system types.
Selecting among the three systems described is not cut and dry, and often involves a balance
of the key factors since each project, installer, and circumstance is different. Fortunately, there
is no wrong choice. All three system designs will supply sufficient flow and pressure to the
outlets even when the base riser pressure is 40 psi and the length to the farthest outlet is 100
feet. But, the costs and performance of each system do vary for each house design. Selecting
the best system for your project can reduce installation costs, minimize installation headaches,
and lead to more satisfied homeowners.

To aid in the decision-making process, several tools are provided.
1. General Rankings of the Systems for Key Factors – This general comparison will
provide a place to start and compare how the systems stack up based on your priorities.
2. Example Layouts – Detailed layouts of each system are provided for four common house
types. By selecting the type that most closely resembles your project, you can see how the
systems compare for your building design.
3. Performance Testing – The three systems were compared and tested in comprehensive
laboratory tests. By examining the test data you can identify differences in the systems’
performance in varying scenarios.
4. Industry Technical Support – Manufacturers and organizations offer a range of resources
to assist PEX users. The support ranges from general information to technical assistance on
specific projects.

General Rankings of the Systems for Key Factors
The general characteristics of the systems are ranked in Table 7.1. Given the wide difference
between housing designs and preferences, they may not apply in every situation, but are useful
for general guidance as you design your home. The best way to use the table below is to
establish the relative priority of key factors, and use the rankings of system designs to provide a
starting point for the system to be selected.
For example, if when considering the factors in the table below, you determine that your top
three factors are:
1. Minimizing Fittings and Joints5
2. Centralized Shut-off Valving
3. Pressure Stability with Use of Multiple Fixtures
Then, given the fact that the home-run system ranks at the top of all three, it is a logical place
to start. However, if your top factors give you three different best designs, the right choice is
not as obvious. You will then need to consider other factors, and further explore the detailed
design of your home to make a choice. The example layouts later in this chapter may then be
helpful in making a choice.

Cost has been omitted as a factor in this guide. Since local labor costs vary, and there is
variation between the fitting and piping costs offered by different manufacturers, this guide
simply provides information on the amount of pipe and fittings needed. Since the balance
between material and labor cost varies across the country, the determination of actual cost
estimates and total cost comparison between system designs is left to the designer or installer.

Example Layouts
The following plumbing system layouts provide supply water diagrams and estimated fittings
and piping descriptions for the four most common house types: Colonial, Ranch, Townhouse,
and Condominium. Each house type has three piping layouts that illustrate each of the three
system designs. Piping lengths, and fitting and joint counts are provided for each system to
provide a comparison of material use and labor required. You can select the home design that
most closely resembles your home design to help select the system that is right for you. Note
that in these designs, few obstructions are accounted for and thus represent idealized pipe runs
with a minimum of fittings.

Colonial Layout
The Colonial house layout has approximately 2,000 square feet of floor area. The water main
enters the house under the unfinished basement slab. The water heater is located near the
main water line in the basement. The first floor has a living room, dining room, kitchen, family
room, and a powder room. The second floor has four bedrooms, two full baths, and the
clothes washer.

In larger homes with a large separation between bathrooms, the trunk and branch design uses
the least amount of total pipe but the most fittings and joints. The home-run system uses the
most piping (2.4 times on average) and the least amount of fittings and joints. While the homerun system uses more piping, the piping has a smaller diameter which is easier to handle and
install, particularly around bends. An appropriate balance between labor and material costs as
well as the relative performance of the systems is important when deciding on a system layout
for your particular house.

Ranch Layout
The Ranch house has approximately 1,300 square feet of one-story floor area. The water main
enters the house under the slab on grade. The one-story floor plan includes a great room,
a kitchen, a dining room, three bedrooms, and two full baths. The water heater and clothes
washer are located in the utility room.

In home layouts with a large separation between fixtures, the trunk and branch design uses the
least amount of pipe followed by the remote manifold design. The home-run system uses the
most piping (1.8 times more on average) and the least amount of fittings and joints. The homerun system uses more piping, but with smaller diameters, which is easier to handle and install,
particularly around bends. An appropriate balance between labor and material costs as well
as the relative performance of the systems is important when deciding on a system layout for
your particular house.

Townhouse Layout
The Townhouse has two stories and is approximately 1,000 square feet of floor area. The
water main enters the house under the first floor’s slab on grade. The first floor has a living
room, kitchen, dining room, and a powder room. The second floor has two bedrooms and one
full bath. The water heater and clothes washer are located on the first floor.

In this more compact house design, the differences between the trunk and branch and remote
manifold systems are primarily in reduced fittings and joints for the remote manifold system.
The home-run system uses considerably more pipe (1.9 times more on average) as the trunk
and branch and remote manifold designs. The home-run system uses more piping with smaller
diameters, which is easier to handle and install, particularly around bends. An appropriate
balance between labor and material costs as well as the relative performance of the systems is
important when deciding on a system layout for your particular house.

Condominium Layout
The Condominium has approximately 1,200 square feet of floor area. It has a living room,
kitchen, dining room, two bedrooms, and two full baths. The clothes washer is located in the
unit. The condominium building has a central plant for water heating; therefore, there is no
water heater located in the unit.

The trunk and branch system uses the most tees which increases the number of joints. The
trunk and branch and remote manifold system layouts are similar in pipe use, but the remote
manifold uses fewer fittings resulting in fewer joints. The home-run system uses the most pipe
(1.8 times more on average) and the least amount of fittings. The home-run system uses more
pipe with smaller diameters, which is easier to handle and install, particularly around bends. An
appropriate balance between labor and material costs as well as the relative performance of
the systems is important when deciding on a system layout for your particular house.

Performance Verification Laboratory Testing
A set of laboratory tests using typical plumbing fixtures and plumbing pipe sizes, runs and
fittings was performed to demonstrate the flow characteristics of the three different PEX
systems. Results of this testing indicate that all three systems will supply adequate pressure
and water delivery to a remote shower fixture located 100 feet from the base riser with an
elevation head of 15 feet. Base source pressures of 40, 60, and 80 psi were used in each of
the different system designs. Multiple tests were performed to add simultaneous flows from
other fixtures including a shower, lavatory, kitchen and water closet.

Industry Technical Support
If you have questions that have not been answered in this Design Guide, you can contact the
PEX manufacturer directly. The following websites provide a wealth of general information on
PEX piping.
Manufacturers of PEX piping and fittings can also provide specific technical assistance during
the design, planning, and installation phases. Contact information for each can be found at the
PPI and PPFA and websites and on the individual manufacturers’ sites.
Plan Pipe Routing, Manifold, and Valve Locations
Once the system design is selected, the final step in the design process is to plan pipe routing,
manifold, and valve locations. As in the case of the home design optimization, there are several
guidelines that can simplify this process. Bear in mind that PEX piping is available in continuous
coils as well as 20-foot straight lengths. Consult the local codes for specific installation
requirements for your project.

Guidelines for optimizing the design of a PEX plumbing system include:
1. Minimize fittings – The flexibility of PEX piping enables it to be easily installed around
obstructions and through framing members. Use of sweep turns (i.e., bending the pipe in
a gentle sweep rather than using solid fittings) to change direction can result in quicker
installations, fewer mechanical fittings, and less resistance due to pressure drops common
through fittings.
2. Group fixtures together – If using trunk and branch or remote manifold, use common
trunk lines to feed multiple fixture groups. For example, if two bathrooms are stacked, use a
single remote manifold to feed both, rather than two remote manifolds.
3. Minimize pipe lengths – Though this may seem intuitive, attention to this detail should
lead to efficiently installed plumbing systems, especially when considering plumbing layouts
using PEX piping.
4. Select appropriate pipe diameter – Many plumbing systems are installed using standard
practices that apply to very large homes but are excessive for smaller homes. Taking a
short amount of time to plan the piping sizes needed to supply the proper flow rates at the
required pressure, will result in the use of pipe sizes that deliver the required fixture flow
rate, but are not oversized. Oversized plumbing system designs result in wasted energy and
water, as well as reduce customer satisfaction with the plumbing system.
5. Bundle pipe runs – Applicable particularly to PEX plumbing runs where few fittings are
installed, installation of multiple piping runs at the same time will reduce installation time.
The flexibility of PEX piping and the long unbroken lengths that can be easily spooled to
enable the simultaneous installation of multiple plumbing lines running in the same direction
using common holes through barriers such as joists.
6. Plan for solid attachment of transition points – The flexibility of PEX piping also
requires that the transition to threaded fittings or rigid piping be performed correctly.
As with most piping materials, solid connection points and solid attachment points are
necessary when threading on valves and transition fittings to other materials.
7. Use color coding – PEX is available in different colors. Using dedicated colors for hot,
cold, and greywater, where applicable, can be helpful for installers, homeowners, and future
retrofits.
Before locating manifolds, determine whether valves will be placed at fixtures or on manifolds.
Some jurisdictions require valves at the fixture, while others allow them to be located on
central manifolds. In some cases the homeowner may express a preference for the location
of shut-off valves. If valves are to be placed on manifolds, they must be situated to allow easy
access. This can be accomplished by placing them behind access panels, or open in basements,
laundry rooms, mechanical rooms, or garages where no freeze potential exists. It is also
important to label each valve on the manifold to ensure easy identification of the distribution
lines. If valves are not placed on the manifolds, and local codes allow, the manifolds may be
enclosed within walls or floors, similar to any other fitting such as a tee or ell.

System Performance Comparison
Each of the three PEX plumbing configurations described in this guide can be installed in most
homes with satisfactory performance. The different systems offer opportunities to optimize
the performance of the plumbing system, reduce the installed cost, and increase overall
customer satisfaction and acceptance. In order to quantify the differences between PEX system
designs, each system was tested in the laboratory to provide a similar set of conditions under
which the systems are installed and operated. Actual residential plumbing fixtures, piping
layouts with fittings, and even elevation changes were installed and operated. This provided
a consistent comparison between system designs, as well as an indication of the minimum
performance characteristics of each system.

PEX piping was installed in each of the three configurations—trunk and branch, home-run, and
remote manifold—with overall results showing:
• All systems had similar flow characteristics at each of the fixtures when flowing
independently
• All system designs responded in a similar manner to simultaneous flow events (more than
one fixture flowing at once)
• Minor differences in the actual measured flow and pressure at a test fixture emerged when
simultaneous flow events occurred

Test System Design and Set-up
A set of plumbing fixtures were installed in a laboratory setting to provide actual flow and
pressure data during operation of the fixtures. These data provide assurance that the PEX
plumbing system design is capable of supplying the required flow rates during operation of the
fixture. In addition, the test results provide assurance that the plumbing system design will
supply adequate flow and pressure to a remote test fixture while other fixtures are operated
simultaneously. The test system was constructed and reconfigured for each type of PEX
plumbing design, including the standard trunk and branch (T&B), the home-run (HR), and the
remote manifold (RM). A primary Test Fixture (TF), represented by a tub/shower unit, was
installed and instrumented to measure flow rate and flow pressure on the hot and cold lines, as
well as mixed water temperature. Figure 8.1 shows the laboratory system diagram for the T&B
system. Other test system designs are shown in Appendix A. The TF was located the farthest
from the source of all the fixtures, and was operated in shower mode during all tests. The
operating performance of this test fixture represents the “worst case” characteristics of the
full system, since all other fixtures were closer to the source. Figure 8.2 shows the laboratory
set-up configured with the fixtures and the T&B system design with 100-foot distance to the TF
These fixtures were connected to the three different PEX plumbing configurations. Tests
included using two different total distances of pipe run to the farthest TF, 100 feet and 60
feet. The piping runs to the other fixtures were run in lengths that matched the type of piping
system installed (i.e., if the HR system was being tested, all fixtures are plumbed with the HR
system).

Diagrams of all the test piping arrangements are shown in Appendix A.
Two sets of tests were performed for each plumbing system. One test recorded pressure and
flow data at the TF, while other fixtures were operated. A second set of tests was performed
to measure the length of time it took for hot water to reach the TF. The test was started after
the piping was stabilized to the incoming water temperature.

Plumbing System Pressure and Flow Test Results
For all pressure and flow tests, the farthest shower fixture (TF) was operated in the shower
“full-on” mode. The flow pressure and flow rates for each of the hot and cold water supplies to
the TF were recorded. During the operation of the TF, other simultaneous flows were added
as described in Table 8.2. For this, the TF flow and pressure data were recorded as well as the
total hot and cold water supply to the other fixtures and the pressure at the base of the riser.

Flow and pressure measurements were recorded for each of the tests and are recorded in
Table 8.3. Each system was tested at three different static pressures measured at the base of
the riser, 40, 60, and 80 psi. Table 8.3 shows the results of the TF flowing with no simultaneous
fixtures operating.
The performance data for each of the three system designs shows very similar performance for
both the 100-foot distance to the TF and the 60-foot distance to the TF. At 100 feet from the
source, the TF flow rate on the hot side of the valve was the primary flow and was 1.5 gpm at
a low pressure of 40 psi (static). The flow rate at the valve increased to 2.4 gpm for the 60-foot
distance with a riser pressure of 80 psi (static).
Once the baseline flow performance was verified for the TF, additional tests were performed
adding simultaneous flows in conjunction with the TF flowing. The performance measure of the
system capability to supply the farthest fixture is the flow and pressure data at the TF. Table 8.4
shows the performance data for the 100-foot tests with a source pressure of 40 psi.

The system performance with simultaneous flows was very similar to the previous 100-
foot test but with slightly lower pressure drops. A static pressure of 40 psi is considered to
be a minimum supply pressure. A summary of the results for the simultaneous flow system
performance at 60 and 80 psi source static pressure is shown in Appendix A.
Comparing the flow pressure and flow rate is a good way to determine the performance of a
plumbing system. The limitation is that the pressure at the base of the riser is dependent on
the size of the service line, meter, and water utility supply pressure. In order to describe and
compare the performance of each type of system, the pressure drop from the base of the
riser to the farthest outlet (including elevation losses) can be evaluated. Figures 8.4 and 8.5
show the comparison of pressure drop based on various outlets in the system flowing with the
resultant pressure drop at the farthest fixture. Both figures indicate that the home-run system,
while having a higher pressure drop to the TF, has a more consistent pressure drop during
simultaneous flow. The other systems, based on the trunk line feeding branch lines, continued
to show increasing pressure drop as more fixtures were added to the system. In fact, when the
full set of fixtures was operating simultaneously, the trunk and branch system pressure drop
exceeded that of the home-run and the remote manifold configurations. (The remote manifold
system is highly dependent on the system design, i.e., the location of the manifolds and the
number of fixtures connected to the manifold).

Wait Time for Hot Water
A significant benefit of PEX piping systems is the opportunity to reduce water and energy
waste by reducing the amount of time to deliver hot water to the outlet from the water heater.
Though hard to quantify definitely, there are indications that hundreds of gallons of water per
year are wasted while waiting for hot water to reach the outlet.
Tests were also performed on each of the three PEX system designs to compare the time it
takes for hot water to be delivered to the test fixture (TF). Figure 8.6 shows the results of
delivering hot water to the shower fixture after the pipes were flushed with cold (city) water.
The results were normalized to keep the flow rates and temperature from the hot water tank
constant for all systems.
Figure 8.6 – Comparison of Hot Water Delivery Time
Water and time savings of between 30 percent and 40 percent were identified based on this
analysis of the home-run system over either the trunk and branch or remote manifold system
designs.

Test Summary
A summary of the performance characteristics of each system is shown in Table 8.6. The data
indicates:
• Trunk and branch and remote manifold systems will supply one fixture at a higher pressure
• Home-run systems will supply a more stable pressure to each fixture when operating
simultaneous fixtures
• Home-run systems will deliver hot water to the outlet quicker, especially when the pipes are
at room temperature
• Trunk and branch and remote manifold systems will deliver hot water quicker during
sequential flows
• All three system designs will supply sufficient flow and pressure to the outlets even when
the base riser pressure is 40 psi and the length to the farthest outlet is 100 feet.

STALLATIo
Cross-Linked Polyethylene (PEX)
Hot- and Cold-Water distribution Systems
This chapter is extracted in its entirety from the Plastic Pipe and Fittings Association (PPFA)
document entitled “Cross-Linked Polyethylene (PEX) Hot- and Cold-Water Distribution
Systems,” released in 2006, and is included with permission from the PPFA. It is provided as
a general reference to supply basic information regarding the installation process for PEX
piping in residential water service applications. It should not be used in place of the specific
manufacturers’ instructions for the installation of any particular system. Local codes provisions
may vary, and should be consulted before beginning any piping installation.

Important Notice
The information in this manual was gathered from publicly available sources, including reports
of tests conducted by various independent entities under the test conditions specified in the
standards listed.
The contents of this manual are informational only and are not intended as an endorsement or
warranty with respect to any product or system.
The Plastic Pipe and Fittings Association (PPFA) and its members have no responsibility
for the design, administration, results, or evaluation of any test. PPFA and its members
make no warranties, express or implied, as to: the fitness of any product or system for any
particular purpose; the suitability of any product or system for any specific application; or the
performance of any product or system in actual construction.
No product or system shou d be used or insta ed w thout first rev ew ng a l app cab
umb ng or bu ng code prov ons and the manufacturer’s insta at on or app cat on
nstruct ons. Local code author es and the product or system manufacturer shou d be
consu ted w th respect to unreso ved quest ons or uncerta nt es.
In the event there is any confl ct or incons stency between the content of th s manual and
the applicable building or plumbing code and the manufacturer’s installation or application
instructions, the codes and the instructions shall be followed.

Revision Policy
The PPFA Flexible Polyolefin Hot and Cold Water Systems Product Line Committee is
responsible for revision of the manual. All suggestions and recommendations for revisions
shall be addressed to the Committee, which shall respond to them as promptly as reasonably
possible. The Committee shall review the manual in its entirety at least once every three (3)
years.

Manual Content & Use
This manual contains information on the installation of Cross-linked Polyethylene (PEX) tubing
for hot- and cold-water distribution systems in residential and light commercial installations
using tubing up to 1 inch diameter.
Information in this manual shall not be separated as it is often interrelated.
Consult local codes for additional installation requirements.
For additional information contact:
Local officials having jurisdiction (for codes)
Manufacturer (for specific product information)
PPFA (for general installation instructions)
Plastics Pipe Institute (PPI)

Other Uses of Cross-Linked Polyethylene (PEX) Tubing
Hydronic Radiant Heating
Heat Pump Applications
Other Uses with Similar Service Requirements
Consult tubing manufacturer for details.
 

Fitting Identification
All fittings shall be marked with manufacturer’s name or trademark or other identification
mark, plus the ASTM standard specification with which the fitting complies.

Applicable Standards
• ASTM F 876 - Specification for Cross-linked Polyethylene (PEX) Tubing
• ASTM F 877 - Specification for Cross-linked Polyethylene (PEX) Plastic Hot and Cold
Water Distribution Systems
• ASTM F 1807 - Specification for Metal Insert Fittings Utilizing a Copper Crimp Ring for
SDR 9 Cross-linked Polyethylene (PEX) Tubing
• ASTM F 1960 - Specification for Cold Expansion Fittings with PEX Reinforcing Rings for
use with Cross-linked Polyethylene (PEX) Tubing
• ASTM F 2159 - Standard Specification for Plastic Insert Fittings Utilizing a Copper
Crimp Ring for SDR9 Cross-linked Polyethylene (PEX) Tubing
• ASTM F 2080 - Standard Specification for Cold-Expansion Fittings With Metal
Compression-Sleeves for Cross-Linked Polyethylene (PEX) Pipe
• ASTM F 2098 - Standard Specification for Stainless Steel Clamps for Securing SDR9
Cross-linked polyethylene (PEX) Tubing to Metal Insert Fittings
• CSA B137.5 - Cross-linked Polyethylene (PEX) Tubing Systems for Pressure
Applications

Limitations on PEX Use
Do not use in applications where the temperature of the water could exceed 180oF at 100
psi unless specifically approved in the code, e.g., water heater relief line. See manufacturer’s
recommendations for higher operating temperatures at lower pressures.
Do not use in any application where tubing will be exposed to direct sunlight.
Do not allow tubing to come in extended contact with any of at least the commonly
encountered construction materials listed below: (This list is not all-inclusive.)
• Pipe thread sealing compounds
• Fire wall penetration sealing compounds. Exception: water soluble, gypsum-based
caulking or other sealants approved by the PEX tube manufacturer
• Petroleum-based materials or sealants such as:
• Kerosene, Benzene, Gasoline, Solvents, Fuel Oils, Cutting Oils, Asphaltic Paint,
and Asphaltic Road Materials, Acetone, Toluene, and/or Xylene
Consult your tubing manufacturer if you have questions about these or any other materials not
listed.
Do not place any PEX tubing in heavily contaminated soils or other heavily contaminated
environments.
Do not use tub ng w th gouges, cuts, cracks, abras ons, evidence of chem cal attack, or other
defects, or tub ng wh ch has been crushed or k nked.
Do not use PEX in sw mm ng pool p ng systems.
Copper or brass fitt ngs, when used in a PEX p ng system, have the same l tat ons as
copper or brass fittings used in plumbing or heating systems.
Store fittings in containers that are free of oil, grease, lubricants, solder flux, or other
chemicals and away from corrosive atmospheres (Example: Ammonia).

TUBING INSTALLATION PRACTICES
General Installation
Review all limitations on the use of cross-linked polyethylene tubing, and the fitting system you
have selected to use.
Keep tubing a minimum of 12 inches vertically or 6 inches horizontally from sources of high
heat, such as recessed light fixtures, flue gas vents, or heating appliances.
Do not install PEX tubing downstream of
any point-of-use water heater or immersed
coil heater in a boiler where the output
temperature can exceed 180oF or closer than
6 inches upstream. Contact manufacturer for
recommended metallic transition fittings.
PEX tubing may be connected directly to
residential electric water heaters, if the local
code and manufacturer’s instructions allow.
When connecting PEX tube to gas water heaters, the tube must be kept at least 6 inches away
from the exhaust vent of the heater. Flexible metal water heater connectors may be needed in
some instances.
Hose bibbs shall not be supported by PEX tubing. Hose bibbs shall be
anchored to prevent strain on PEX tubing.
Use only continuous length tubing (no fittings) when installing PEX
under or within a slab. Protect PEX tubing with nonmetallic sleeves
where it penetrates a slab or foundation. (Examples: PVC bend guides,
PE sleeving). Protect tubing from nail damage where
appropriate.

Bending the Tubing
Do not bend PEX tubing tighter than the following minimum recommended bending radii.

Handling and Storing Tubing and Fittings
Do not drag the tubing over rough terrain, Do not crush or kink the tubing.
rocks, or any surface that can cut, puncture,
or damage the tubing wall.
Inspect all tubing and fittings before and
after installation. Cut out and replace all
damaged sections or fittings.
Tubing shall be stored in a way to protect
the system from mechanical damage (slitting,
puncturing, etc.). Tubing and fittings shall be
stored undercover for cleanliness and to avoid
exposure to sunlight. Consult manufacturer for
recommended limits for outside storage.

Tubing Supports:
Selection and Inspection
ast c hangers and straps are recommended, but metal supports wh ch are des gned for use
with plastic tubing can be used.
Do not use supports that pinch or cut the tubing.
Support should allow free tubing movement.
Inspect all supports prior to installation to ensure that
sharp edges do not exist that can damage the tubing.

Support Spacing and Location
Horizontal Tubing Support Spacing
Nominal Tubing Diameter (in.) Spacing (in.)
3/8, 1/2, 3/4, 1 32
Vertical tubing shall be supported at every floor (8-feet to 10-feet height) and at the mid-floor
guide between floors.
When penetrating metal studs, utilize a properly-designed bushing or sleeving material on all
penetrations to protect tubing.
Tubing and fittings shall be installed without placing stress on the connection. Stress on
connections frequently occurs when tubing is not properly strapped at changes of directions.
See i ustrat ons for proper methods.

Expansion/Contraction of Tubing
Do not pull tubing tight during installation. This can cause excessive tensile forces on fittings
and connections when tubing cools and contracts. Allow 1/8-inch slack per foot of installed
tubing. Expansion can usually be accommodated by the tubing’s flexibility for sizes up to and
including 1 inch.

Hydraulic Shock (Pressure Surge)
The following table provides the maximum pressure that will occur from rapid closure of a
valve in the various tubing systems at a given velocity. The faster the velocity, the greater the
potential hydraulic shock (pressure surge).
Excessive hydraulic shock (pressure surge) may result in audible water hammer with metallic
piping systems, though this is highly unlikely with PEX tubing due to the flexibility of the tubing
itself.
The table shows the additional hydraulic shock (pressure surge) that can occur in various types
of pipes at the water velocities shown when a fast-acting valve closes. Hydraulic shock pressure
is in addition to the system static pressure (measured on site). To determine the instantaneous
total system pressure that occurs, add the hydraulic shock pressure to the static pressure.
For normal plumbing installations, water hammer arrestors are not necessary with a PEX
tubing system.
In predominantly metal piping systems in which PEX is used, it may be necessary to install
water hammer arrestors.

Manifold Plumbing Systems
The para el man fo umb ng concept is re at ve mp e. Each faucet or water out et is fed
by its own ded cated l ne wh ch runs from a central man fo d. By provid ng each out et w th its
own d str but on l ne, the system offers qu eter water flow, more ba anced water pressure, a
dramat c reduct on in the number of fitt red, and the ab ngs requ ty to save both water and
energy, versus traditional system designs.
The following information applies to a PEX tubing plumbing manifold system in addition to the
general limitations and installation information on PEX tubing and fittings in this manual.
• Manifolds can be installed in a horizontal or vertical position.
• In larger installations, with multiple water heaters, remote manifolds may be used to
handle groups of remote outlets.
• Each faucet or water outlet is fed by its own dedicated line from the manifold, which
may be located near the water supply or water heater.
• Tubing shall be run continuously and as directly as possible between manifold and
fixture locations. Approved fittings may be used to repair kinked or damaged PEX
distribution lines, or to add to a distribution line that was mistakenly cut too short
during installation. Excessive use of fittings is unnecessary.
• Shut-off valves can be placed at the manifold or fixture. Check with your local
inspector.
• Tubing shall not be pulled tight. Leave slack to allow for expansion and contraction.
• Install tubing cautiously to avoid binding, kinking, or abrasion.
• Leave excess tubing at the beginning and end of runs for connection to fixtures and the
manifolds.
• When running lines to a group of fixtures, they may be bundled together, but must be
bundled loosely enough to allow individual tubing movement. Plastic ties may be used.
• Do not use tape when bundling tubing as it may restrict movement of tubing runs.
• When bundled lines pass through conventional structural members, cut a hole at the
centerline of the member. Consult the applicable code for maximum allowable hole
size.
• Identify and mark all lines at the manifold.

Manifold Plumbing Systems:
Parallel Water Distribution Manifold Plumbing (Home-Run)
Systems
Each faucet or water outlet is fed by its own dedicated line from the manifold. Manifolds for hot
water should be installed near the water heater to minimize hot water delivery time. Manifolds
shall be installed at least 36 inches away vertically, or 18 inches away horizontally from the
water heater. A manifold for cold water only may be installed near the water supply.
The following information applies to a PEX tubing plumbing manifold system in addition to the
general limitations and installation information on PEX tubing and fittings in this manual.
• Manifolds can be installed in a horizontal or vertical position.
• In larger installations, with multiple water heaters, use a manifold at each water heater
for the fixtures served by the water heater.
• Tubing shall be run continuously and as directly as possible between manifold and
fixture locations. Approved fittings may be used to repair kinked or damaged PEX
distribution lines, or to add additional length to a distribution line that was mistakenly
cut too short during installation. Excessive use of fittings is unnecessary.
• Shut-off valves may be placed at the manifold or at the fixture. Check with your local
inspector for the local requirements.
• Tubing shall not be pulled tight. Leave slack to allow for expansion and contraction.
• Install tubing cautiously to avoid bending, kinking, or abrasion.
• Leave excess tubing at the beginning and end of runs for connection to fixtures and the
manifolds.
When runn ng l nes to a group of fixtures, they may be bund ed together, but must be
bund ed loose y enough to a ow ind vidual tub ng movement. P ast es may be used.
Hot and co nes may be bund ed together but some jur sd ct ons do not perm t th
pract ce. Be sure to check w th the local author ty.
Do not use tape when bund ng tub ng as it may restr ct movement of tub ng runs.
• When bundled lines pass through conventional structural members, cut a hole at the
centerline of the member. Consult the applicable code for maximum allowable hole
size.
• Identify and mark all lines at the manifold.
• Manifolds shall be accessible and protected from freezing and exposure to sunlight.
Hot water and cold water manifolds shall be sized in accordance with the following table:

Individual fixture shutoff valves may be installed at the manifold if permitted by the local
authority. If installed, they shall be identified as to the fixture being supplied.
Individual distribution lines supplied from a manifold and installed as part of a parallel water
distribution system shall be sized in accordance with the following table:
 

Thawing PEX Tubing Systems
PEX tubing systems should not be intentionally subjected to freezing.
Do not use open torch or excessive heat to thaw PEX tubing.
Tubing failure or damage can result. Use a hot air gun or a blow
dryer.
Heat (DO NOT USE A TORCH) must be applied directly to the
frozen tubing section. Temperature on tubing shall not exceed
180oF.
Several suitable methods exist to thaw PEX tubing. They include:
• A commercial system which pumps heated water through the tube to the ice blockage,
and returns the cooled water for reheating
• Wet hot towels
• Hot water
• Hand-held hair dryer
• Low wattage electrical heating tape

Pressure Testing and Inspection of the Completed System
Test system w th water.
Test pressure sha l be at least equal to the expected work ng pressure (ma n pressure), but not
ess than 40 psi and not greater than 225 psi at 73°F.
Compressed air testing is only recommended when water is not available or when cold
weather could freeze the system. Compressed air tests shall include appropriate safety
precautions and the test pressure shall not exceed 100 psi. PEX tubing is ductile and will not
shatter during a pressure test and release shards of plastic. However, plastic fittings or other
system components, or unassembled fittings, may cause a hazard. Check with local codes
before using air pressure testing.
Test duration should not be less than 15 minutes.
Do not allow water in system to freeze.

Disinfection of Potable Water Systems
If disinfection of the system is required by code, and the conditions are not specified, the
following procedures can be used.
Chlorine Concentration Disinfection Period Authority
50 to 100 ppm 3 hours AWWA*
50 ppm 6 hours ICC**
*American Water Works Association
** International Code Council
Use one of the recommendations above.
Pre-mix the solution before injection into the system.
Thoroughly flush all lines of the system at the end of the disinfection period.
Failure to do so may damage the plumbing system.

Buried PEX Water Service Lines
Fittings
Consult manufacturer for proper fittings for water service application.
Trench Preparation
Trench bottom shall be solid with no hollows, lumps, rocks, or other materials that could
damage the tubing.

Laying the Tubing
Tubing should be laid with sufficient slack (snaking) to accommodate any contraction due to
cooling prior to backfilling. Tubing will expand or contract approximately 1 inch in length for
each 10°F change in tubing temperature for each 100 feet of tubing.
Minimum bending radius requirements for PEX tubing shall be followed. See “Bending the
Tubing” Table.
Inspect tubing for damage. Remove and replace damaged sections.
In poor soil conditions, such as mud, rock, black gumbo, or clay, it is necessary to excavate
deeper and use good clean fill or granular fill to smooth the trench bottom.

Penetrating Foundation or Basement Walls
When PEX is run through a basement or foundation wall, it must be protected by a rigid sleeve
that spans the distance from within the wall out to the undisturbed soil in the pipe trench.
The purpose of this protective sleeve is to prevent shearing of the PEX tubing at the wall in
the event there is settlement in the backfill around the wall. At the point where the sleeve
terminates inside the foundation or wall, the space between
the PEX and the sleeve should be sealed to prevent leakage
into the building.

Slab-on-Grade Installation
Laying and Supporting Tubing under Slab
On y cont nuous y-run engths of tub ng w thout fitt ngs sha be used when nsta ng PEX under
a slab. All connections shall be outside or above the slab. Tubing shall be completely buried by
a suitable, easily compacted, backfill material such as sand or pea gravel. PEX tubing should be
installed under the rebar, re-mesh, or tensioning cables in the slab. PEX tubing shall be covered
or fastened to prevent the tubing from floating or being pulled up to the slab surface.
PEX tubing does not have to be sleeved its entire length where it lies beneath a slab. PEX
tubing shall be protected with a non-metallic sleeve where it comes through the slab. Because
PEX is flexible, it may need support to keep it from falling back onto the slab once it exits the
slab. To prevent this, PEX can be carefully tied to re-bar, wood stakes or rigid drain pipe for
support. This will serve to protect the PEX tubing as the slab is poured, leveled and smoothed
and from subsequent framing and construction work.

Protection of Tubing and Fittings from UV Exposure
after the Pour
Due to the nature of slab-on-grade installations, tubing and fittings may be exposed to UV
light for unspecified periods of time after the slab is poured and before the structure is framed
and enclosed. To prevent damage from UV exposure, PEX tubing and fittings that are exposed
above the slab shall be wrapped with an opaque covering such as black polyethylene bags or
sheeting immediately after the pouring of the slab. This covering should extend down to the
surface of the slab to protect all of the tube above the slab from excessive UV exposure. For
specific limitations on UV exposure, consult the PEX tube manufacturer.

Backfilling
Do not use clay, silt, or rocky backfill. Remove the construction materials, trash, or foreign
objects from trench prior to backfilling.
The tubing and fittings should be surrounded with good clean fill, or sand, or river run gravel of
1/2-inch maximum particle size.
Compact the initial backfill around the tubing to provide adequate tubing support and
prevent settlement. It is particularly important to adequately compact the soil around the tap
connection.
It is recommended that the tubing be pressurized with water prior to backfilling to reveal any
damage.

Connection (Transition) to Other Piping Materials
Solder copper transition fittings onto the copper pipe and allow cooling before connecting to
PEX tubing. High heat (greater than 180°F) may damage the PEX tubing.
Do not use plastic male threads or non-gasketed female threads when making a connection to
metal threads. Use only manufacturer’s recommended transition fittings.
When making connections to CPVC pipe or fittings, use only approved transition fittings.

Joining Procedures Utilizing Metallic or Polymer Insert Fittings
Insert Fitting with a Black Copper Crimp Ring (ASTM F 1807 OR
ASTM F 2159)
Making a Connection
1. Cut tubing squarely, remove burrs, and slip the copper crimp ring onto the tube.
2. Insert fitting into tube to the tube stop; do not apply lubricant or pipe dope on the
insert fitting. Position crimp ring 1/8 to 1/4 inch from end of tubing. To prevent ring
from moving, squeeze the ring slightly with your fingers or a pair of pliers.
3. Center crimping tool jaws over the ring. Keeping both ring and tool square with tube,
close the tool completely. DO NOT CRIMP TWICE.
4. It is recommended that the finished crimps be checked with the appropriate GO
NO/GO gauge. Slip gauge squarely over the crimped ring. If the “GO” slot of the gauge
doesn’t fit across the crimped ring, the diameter of the ring is too large and the fitting
must be cut out. DO NOT RECRIMP.
5. If the “NO/GO” slot of the gauge fits across the crimped ring, the diameter of the ring
is too small and the fitting must be replaced. Cut out the ring and fitting, and replace
them.

Incorrect Connections
The consequence of not following correct procedures is a potential for leaks.
• Ring crimped over end of tube
Result: Doesn’t cover enough ribs and/or tool could crush or crack fitting
• Tool not at 90 degrees to tube when crimped
Result: Insufficient rib coverage; tubing dented
• Ring not completely covered by crimp tool
Result: Ring distortion, non-uniform crimp
• Tubing not cut squarely
Result: Insufficient rib coverage
• Ring too far from pipe end
Result: Insufficient rib coverage

Tools and Rings
Use too s recommended by fitt ng and tub ng manufacturers.
l too s must make a fu -c rc e cr mp.
Check tool adjustment at least da y and readjust as necessary.
Use only black-colored crimp rings designed for this PEX system.

Joining Procedures Utilizing ASTM F 1960 Fittings and PEX Rings
1. Cut the PEX tubing perpendicular to the length of the tubing using a cutter designed
for plastic tubing. Remove all excess material or burrs that might affect the fitting
connection.
2. Slide the PEX Ring over the end of the tubing.
3. The PEX Ring should extend over the end of the tubing no more than 1/16 inch. The
end of the tubing and inside of the PEX Ring must be dry and free of grease or oil to
prevent the PEX Ring from sliding out of place during expansion.
4. Place the free handle of the tool against your hip, or place one hand on each handle
when necessary. Fully separate the tool handles and insert the expander head into the
end of the tubing until it stops. Be sure you have the correct size expander head on
the tool. Full expansion is necessary to make a proper connection. Bring the handles
together to expand. Separate the handles, remove the head from the tubing and rotate
it 1/8 turn. Slide the tool head into the tubing in the newly rotated position and expand
again.
5. Repeat the expansion process until the tubing and ring are snug against the shoulder on
the expander head.
6. Immediately remove the tool and slide the tubing over the fitting until the tubing
reaches the stop on the fitting. As you slide the tubing over the fitting, you should feel
some resistance. If the tubing reaches the shoulder of the fitting without any resistance,
the tubing may be over-expanded and may require additional time to fully shrink over
the fitting. To ensure a proper connection, the PEX Ring must be seated up against the
shoulder of the PEX fitting.
7. At minimum, ASTM F 1960 connections must be pressure tested to the system’s
working pressure. PEX tubing and fittings are safe for air and hydrostatic testing. Refer
to your local code for additional requirements.

ASTM F 1960 Connections, Helpful Hints
• Holding the tubing in the expanded position increases the time it takes for the tubing
to shrink around the fitting.
• The tubing should hold the fitting firmly after just a few seconds. If the fitting appears
loose for more than a few seconds, the tubing has been over-expanded.
• If there is more than 1/16 inch between the PEX Ring and the fitting, square cut the
tubing 2 inches away from the fitting and make another connection using a new PEX
Ring.
Incorrect
• Ring does not meet the pipe stops on the fitting. Tubing and rings should both meet the
pipe stops on the fitting.
Incorrect
• Tubing does not meet the pipe stops on the fitting. Tubing and rings should both meet
the pipe stops on the fitting.
Incorrect
• Tubing and ring do not meet the pipe stops on the fitting. Tubing and rings should both
meet the pipe stops on the fitting. Tubing is not cut square.

Tools
There are a var ety of PEX expander too s that are des gned for ease of use when mak ng
re ab e, permanent connect ons.

Joining Procedures Utilizing ASTM F 2080 Fittings and
Compression Sleeves
Summary
Fittings shall be joined to PEX pipe by first expanding the end of the pipe with the expander
tool, inserting the cold-expansion fitting into expanded pipe, then pulling the compressionsleeve over the PEX pipe and the fitting, compressing the pipe between the compression sleeve
and the fitting.

Procedure
1. Slide the compression sleeve onto the pipe so that the inside-beveled end is facing
toward the end of the pipe. Slide the compression-sleeve far enough down the pipe so
that it will not prevent expansion of the pipe.
2. Insert the head of the expander tool into the pipe. The expander tool segments shall
be centered inside the pipe.
3. Fully expand the pipe, holding it open for approximately 3 seconds, and remove the
tool. Rotate the tool approximately 30°, insert the expander-tool into the pipe and
repeat the expansion process. This ensures that the pipe is round inside.
4. The cold-expansion fitting should be inserted within 30 seconds of the expansion;
otherwise the pipe will shrink back to its original size and become too small for fitting
expansion. The fitting is properly inserted when the PEX pipe is pushed up against the
last rib of the cold-expansion fitting. If full insertion is not possible, remove the coldexpansion fitting immediately and expand the pipe again for 3 seconds.
5. When the expansion is complete, and the cold-expansion fitting is inserted properly
into the PEX pipe, the metal compression sleeve shall be pulled over the fitting with
the compression tool (this may be the same tool as the expander tool or a separate
tool).
6. Use the compression tool to pull the compression sleeve over the cold-expansion
fitting and the PEX pipe end until the sleeve touches the collar of the fitting or until the
tool stops.
7. The maximum allowable gap between the edge of the compression sleeve and the
collar of the cold-expansion fitting shall be 0.040 in. If this gap is too large, then repeat
the compression step and/or adjust the tool.

Other Fitting Systems
Some PPFA Members have proprietary fitting systems for which ASTM standards have not
been written. These systems are typically listed as meeting the performance requirements of
ASTM F 877 for PEX systems but their fitting dimensions and materials have not been specified
in a standard. These fittings are typically available only through a single manufacturer and
the components of the system do not interchange with similar looking parts from a different
manufacturer. When using these systems, users are cautioned to be sure they do not mix
components from different manufacturers even if they look the same.

Don Carpenter, Director of Product Development
Oakwood Homes of Denver, Colorado
As part of the Partnership for Advancing Technology in Housing (PATH) Program, administered
by the U.S. Department of Housing and Urban Development (HUD), a Field Evaluation of
technologies was conducted at Green Valley Ranch in Denver, Colo. According to Don
Carpenter of Oakwood Homes, the company began using PEX piping with a central manifold
and home-run system in 2000, after hearing of reduced labor, shortened construction cycle
time, and decreased long-term costs. However, cost savings isn’t the only reason the company
chooses PEX pipe. “We look at it from a quality standpoint,” said Carpenter, director of
product development. “It’s less money to install, and it’s a superior plumbing system. For the
homeowner, it’s control over every fixture in the house, and the ability to easily adapt the
plumbing when adding fixtures, building additions to the house, or finishing the basement.”
Oakwood saves the buyers an average of $800 per home because of the PEX piping system
chosen for the indoor plumbing system.

Rodney Ketzner, Plumbing Supervisor
Plumbing Specialists Inc., Wichita, Kansas
“The system goes in almost twice as fast as copper systems. After a new house has been
framed, I walk through the house with the homebuyer to discuss fixtures and plumbing issues,
including manifold plumbing systems using PEX. We offer conventional copper as an option but
after I explain the system and the benefits it offers, homebuyers almost always choose it.”
“My customers also like the quietness of the system. It’s designed with both the homeowner
and the plumbing contractor in mind.”

Kenny Hodges, Owner
Hodges Plumbing, Blackshire, Georgia
“The owner said it was a good system and he’s right. I wish I had used it in my own home!”

Alan Boone, Plumber
Middleton Plumbing, Statesboro, Georgia
“My supplier mentioned that we could save a lot of time on installation with the PEX plumbing
system. The PEX we used was much easier to install and required very few fittings. The red and
blue color-coded pipe also made the installation go in quickly and easily identified hot and cold
lines. It’s a great choice on large-scale projects. If we’d gone with copper, we’d still be there
working.”

Tony Partusch, Shop Foreman
Partusch Plumbing, Anchorage, Alaska
“With our climate, copper doesn’t work very well. We see a lot of problems with copper
sweat joints leaking. With PEX systems we’ve been able to eliminate 90 percent of the
copper sweat joints in a system and now the chance of having a leak at a sweat joint is nearly
nonexistent.”
“Usually you have to pay a lot more when you upgrade to a better product but PEX manifold
plumbing systems are easy to sell because it’s a better product for about the same price.”

Jim Manning, President
Interstate Plumbing & Air Conditioning, Las Vegas, Nevada
“[PEX] tubing is clean, doesn’t corrode, and it’s not affected by corrosive water and soil. It even
comes with a 25-year warranty. We wanted a system that would save us time, eliminate our
copper theft problem, and ensure quality and reliability. [PEX] has proven itself to be a system
that can do all this and more.”

Don George, Owner
Modern Plumbing, Portland, Oregon
“We’ve been installing [PEX] for years in custom homes. We utilize manifolds in most of our
installations and our customers are continually impressed with how quiet the system is.”

Chris McGinnis, Owner
Tucson Plumbing and Heating, Tucson, Arizona
“The [PEX] connection is the most positive connection available. My plumbers can tell just by
looking at the fitting if they’ve made a good connection. With [PEX], the installation is fast and
easy, and the tubing can be buried directly in concrete—something the codes won’t allow us
to do with copper. My plumbers like the ease of installation provided by the [PEX] fitting and
the time savings that result. Rigid systems … require more connections and more time without
the assurance of a positive connection. With [PEX], we have eliminated many of our callbacks,
which is also a nice benefit.”

Vince Lopoarchio and Levon Paul, Plumber and Project Foreman
VHL Plumbing, Burbank, California
Second generation plumber Vince Lopoarchio states, “The best thing is there are no leaks so
when we’re done we’re done.”
VHL and the developer benefited with consistent connections, no leaks, flexible pipe, no
solder, no flux, and no flame which made for a cleaner, more secure, and faster installation
process. Running 1 inch, 3/4 inch and 1/2 inch PEX tubing, four installers can complete four
typical condo units per day, keeping VHL ahead of schedule.
Veteran installer and project foreman Levon Paul says, “The PEX system is very quiet so our
customers are happy. It’s a pleasure working with this system after 30 years of working with
copper. I would tell anybody that with [PEX] technology labor savings, the hand tools will pay
for themselves on the first multi-unit job.”

 
Radiant Floor Heating Systems
Hydronic radiant floor heating
employs heated water flowing
through flexible PEX pipes
mounted inside or under the
floor. The heated surface
then functions as a radiator,
warming a room and all objects
and people in it. This type
of heating provides superior
comfort and efficiency Figure compared to traditional forcedair convection heating. The
heating profile is much more
uniform, meaning fewer cold/
hot spots.

Municipal Water Service Pipe
In addition to supplying water within the home, PEX pipe is also used to distribute water to
entire communities through municipal water service pipes. Because PEX pipe is more flexible
than other piping materials, it ensures high-impact resistance with normal backfill. PEX pipe is
resistant to freeze damage, lessening the chance of splitting or cracking. It connects to standard
compression joints, valves, and fittings, so it’s easy and convenient to install. It can save up to
half the cost of copper—a significant savings for budget-constrained city planners.

Snow and Ice Melt
PEX pipe can be used to create a hydronic system designed
to augment the removal of snow and ice by circulating a heat
transfer fluid (usually antifreeze and water) through pipes installed
within outdoor surfaces. Common applications are for driveways,
sidewalks, hospital entrances, parking garage ramps, wheelchair
ramps, car washes, hot tub/pool surrounds, and runways. Benefits
include reduced maintenance costs, no snow removal costs,
reduced liability, and obvious convenience.

Articles and Reports
1. Automated Builder Magazine, “PEX Pipe Gains Popularity for Practical
Purposes.” April 2005, page 40. This article presents the multitude of advantages to
using PEX plumbing water supply systems in residential construction, and discusses
the standards and certifications required for PEX pipe and fittings. One home builder’s
experience with PEX and a manifold system is described.
2. Couch, Toro, Oliphant and Vibien, Chlorine Resistance Testing of UV Exposed
Pipe, Jana Laboratories, Ontario, Canada, 2002. Chlorine Resistance (CR) testing is
used to determine the impact of accelerated UV exposure on the oxidative resistance
of cross-linked polyethylene (PEX) pipe. Following accelerated UV exposure, samples
were tested to failure under accelerated test conditions to simulate chlorinated
potable water. For the particular material examined, it was demonstrated that
excellent retention of oxidative stability was achieved when suitable UV protection was
employed.
3. Kempton, William, “Residential Hot Water: A Behaviorally-Driven
System,” Energy, Volume 13, Number 1, January 1988, pages 107-114. This article
reports on the results of monitoring the hot water use in seven homes over 7-18
months. The study shows the wide variation in hot water use among the different
project participants. For instance, water consumption ranged from 44.5 liters per day
per person to 126.4 liters per day per person. Bathing comprised the largest single
water use in all homes but duration and volume varied significantly. The study points
to the potential for water and energy savings through modification of behavior but also
notes that habits related to hot water usage have deep roots in personal, social, and
cultural values. The study also found that most of the participants had misperceptions
related to the duration and amount of their water usage and did not have a firm
understanding of the costs of hot water.
4. Korman, Thomas M. et al, Knowledge and Reasoning for MEP Coordination,
Journal of Construction and Engineering Management, Vo ume 129 Number 6,
November-December 2003, pp. 627-634. “Current y, des gners and constructors
use ta ored CAD systems to des gn and fabr cate MEP systems, but no know edgebased computer techno ogy ex sts to ass st in the mu tid ne MEP coord nat on
effort. The paper describes results from a research project to capture knowledge
related to design criteria, construction, operations, and maintenance of MEP systems
and apply this knowledge in a computer tool that can assist designers and builders in
resolving coordination problems for multiple MEP systems.” This work might provide
background information relevant to developing a knowledge-based design tool for
residential plumbing distribution systems.
5. NSF International, Frequently Asked Questions on Health Effects of PEX
Tubing. This article explains who NSF International is, provides information on NSF
Listed Products for potable water applications, and describes applicable NSF/ANSI
standards for testing and evaluation of potable plumbing.
6. Okajima, Toshio, Computerized Mechanical and Plumbing Design, Actual
Specifying Engineer, Volume 33 Number 6, June 1975, pp. 78-83. “Many mechanical
and plumbing systems designs are based on the engineer’s past experience or educated
guesses. The author tells how one firm developed a computer program for plumbing
and heating, ventilating, and air conditioning design.”
7. Orloski, M.J. and Wyly, R.S., Performance Criteria and Plumbing System
Design, National Engineering Lab, Washington, D.C., 1978. “An overview is presented
indicating how the performance approach to plumbing system design can be used
to extend traditional methods to innovative systems. …Some of the mathematical
models now used for system design and pipe sizing in plumbing codes are reviewed in
the context of performance-oriented research. … Conceivably the re-examination
by plumbing designers of traditional design criteria against measured user needs could
be beneficially extended to other areas of plumbing design such as water distribution,
storm drainage, and plumbing fixtures. Beyond this, it has been recognized that
uniform guidelines for evaluation of innovative systems, based on research findings, are
essential for wide acceptance of performance methods, particularly by the regulatory
community.
8. Rubeiz, Camille, “Flexing Your PEX: Plumbing the Possibilities of Crosslinked Polyethylene Pipes,” Modern Materials, Vol. 2, No. 2, November 2004,
pages 5-8. Properties of PEX pipe are described, as well as benefits of using PEX for
potable water supply plumbing systems. Parallel piping and central manifold system
installations are discussed. Real and misconceived limitations are also presented. In
addition, other applications for PEX pipe systems, such as snow and ice melt and turf
conditioning are mentioned.
9. Rubeiz, Camille & Ball, Michael, “Warming Up to PEX Pipe Radiant
Heating Systems,” Modern Materials, Vol. 2 No. 1, May 2004, pages 14-18. The
article describes how radiant heating works, and compares the radiant heat distribution
to traditional baseboard or forced air systems. There is a general description of the
three methods of cross-linking polyethylene to form PEX piping (radiation, peroxide,
and s ane processes). App cab e ASTM and CSA standard spec ficat ons for test ng of
PEX p pe and fitt ngs are l sted. F na y, the art e br efly d scusses the insta at on of
PEX rad ant heat ng systems in new resident al construct on or remode ng projects.
10. Steele, Alfred, “Plumbing Design Has Ma or Impact on Energy
Consumption,” Specifying Engineer, Volume 45, Number 6, June 1981, pages 80-
83. The paper discusses the potential energy savings that could result from low-flow
fixtures, pipe insulation, and water heater temperature settings. The author emphasizes
that significant water savings and therefore, energy savings as well could be achieved
with no inconvenience to the end-user. It was not until 1994 that the first low-flow
fixtures were introduced in the United States after being federally mandated.
11. Stewart, William E. et al, Evaluation of Service Hot Water Distribution system
Losses in Residential and Commercial Installations: Part 1 – Field/Laboratory
Experiments and Simulation Model and Part 2 – Simulations and Design Practices,
ASHRAE Transactions, Volume 105, 1999. The papers describe a numerical model
developed to estimate the heat loss or gain from insulated and uninsulated, copper and
steel hot water pipes. The authors contend that the simulation model is a more reliable
and consistent method of estimating such losses due to the difficulty of accurately
measuring small temperature differences in field and laboratory experiments. The
results of the simulation model correlate closely with previously published data,
specifically 1997 ASHRAE Handbook – Fundamentals and 1995 ASHRAE Handbook
– HVAC Applications. The simulation results showed more than a 50 percent decrease
in heat loss in hot water piping that was insulated within approximately three feet of
the water heater and that increasing the length of pipe insulated does not significantly
decrease heat loss further.
12. Tao, William & Associates, “Plumbing System Design,” Heating, Piping, &
Air Conditioning, Volume 59 Number 3, March 1987, pp. 101-114. This article outlines
the fundamental criteria to be considered in the design of a building plumbing system.
These criteria include load calculations, system sizing, and special design applications.
A procedure for plumbing system design is also introduced that may serve as a
comprehensive basis for developing computer aided design programs.
13. Vibien, Couch, Oliphant et al, Assessing Material Performance in Chlorinated
Potable Water Applications, Jana Laboratories, Ontario, Canada. In this study, the
nature of the failure mechanism of cross-linked polyethylene (PEX) pipe material
exposed in the laboratory to chlorinated potable water was examined. Based on this
study, the PEX pipe material appears to have good resistance to chlorinated potable
water.
14. Wendt, R.L., Evelyn Baskin, David Durfee, Evaluation of Residential Hot
Water Distribution Systems by Numeric Simulation, Buildings Technology Center,
Oak Ridge National Laboratory for the California Energy Commission, Oak Ridge,
TN, 2004. This study simulated and compared the energy and water performance,
economics, and barriers to use of various domestic hot water distribution systems in
California homes. Variation in systems included trunk and branch, manifold systems,
copper pipe, CPVC pipe, PEX piping, insulated and uninsulated pipe, attic location, slab
ocat on, demand rec rcu at on, and cont nuous rec rcu at on. Us ng a computer mode
LabV ew, the fo ow ng resu ts were found for a c ustered hot water usage pattern:
a. Demand rec rcu at on systems, whether p ng was copper or CPVC, wasted the
east water and the least energy.
b. Whether copper or CPVC piping was used, the system with a centrally located
water heater was second with respect to the least amount of energy wasted.
However, almost twice as much water was wasted in comparison to the
recirculation systems even though the water heater was centrally located.
c. In both groups, the CPVC systems were slightly better energy performers than their
copper counterparts – about 4 to 14 percent better.
d. The parallel pipe configurations using PEX tubing wasted about 3 percent more
energy than uninsulated copper pipe in an attic installation, but wasted 60 percent
less energy than uninsulated copper installed in a slab. Insulating the sub-slab copper
pipe brought its energy performance inline with the PEX system. With respect to
water waste, the parallel system (attic installation) performed similarly to copper
pipe installed in an attic.
e. Sub-slab installation without insulation compromised the energy and water
performance of all the systems. However, the parallel system using PEX pipe suffered
the least – an approximate 30 percent drop in performance compared to a fourfold
decrease for the copper and CPVC systems.
f. Construction costs for the parallel system using PEX tubing were slightly lower than
the trunk and branch system using copper, but higher than the CPVC systems.
While the study indicates that usage patterns have the most significant effect upon
energy usage and water consumption in residential situations, it also postulates that
“parallel pipe distribution systems may offer an attractive alternative for some house
designs and distribution system layouts.” The modeling showed very little difference
in energy and water performance when clustered use was assumed but indicated that
parallel systems outperform conventional trunk and branch systems when cold starts
are typical.
15. Wiehagen, J. and Sikora, J. (March 2003). Performance Comparison of
Residential Hot Water Systems, work performed by NAHB Research Center, Inc.
for NREL. Using data from two research sites in Ohio and from weekly laboratory
experimental data, a simulation model was developed to estimate annual energy
consumption for several types of water-heating systems. Using the Transient Energy
System Simulation Tool, TRNSYS, three types of systems were analyzed under highusage (average 76 gallons per day) and low-usage conditions (average 28 gallons per
day). The systems were 1) a standard electric storage tank water heater with a copper
tree-configuration distribution system, 2) a central tankless water heater with a
polyethylene (PEX) piping parallel distribution system, and 3) multiple point-of-use
water heaters with a copper tree-type distribution system. The simulations showed
a 12 percent increase in overall system efficiency for the tankless water heater with
the PEX parallel piping system compared to the storage heater with the copper treed
system under high usage conditions. For the low-use home, there was a 26 percent
ncrease in effic ency for the same system. The ana ys so ind cated energy sav ngs
for the PEX para el p ng configurat on whether the water heat ng equ pment was
a convent onal tank or a tank ess system – 6 percent sav ngs for the h gh-use home
and 13 percent sav ngs for the low-use home. Ana ys s of the tree-type system w th
mu e po nt-of-use heaters a so showed improved energy performance in compar sonppendix C – rESourCES
to a similar treed distribution system with a storage tank water heater – a 50 percent
reduction in energy consumption for the low-use condition and 28 percent reduction
for the high-use home. In addition to the energy savings, an economic analysis showed
a positive annual cash flow for the parallel distribution systems whether a tank or
tankless heater was used compared to the standard tank/tree system. The analysis
included estimates of installed cost, financing costs, and electricity costs.
16. Wiehagen, J. and Sikora, J. (April, 2002). Domestic Hot Water System
Modeling for the Design of Energy Efficient Systems, work performed by NAHB
Research Center, Inc. for NREL. Using data obtained from actual home sites, the
researchers developed a computer simulation model to analyze typical residential
plumbing systems. The evaluation compared demand water heating equipment in
conjunction with various piping configurations to a standard tank heater with a tree
delivery system. High- and low-usage patterns were considered. Maximum energy
savings resulted from using a combination of a centrally located demand water heater
with a parallel piping system. Annual energy savings were 17 percent for the high
consumption home and 35 percent for the low use home. The demand system did
show some hot water temperature degradation during periods of high flow rates.
17. Wyly, R.S. et al, (May 1975). “Review of Standards and Other Information
on Thermoplastic Piping in Residential Plumbing.” Sponsored by the U.S.
Department of Housing and Urban Development, Washington, D.C. “The paper
is a review of existing information on the physical characteristics of thermoplastic
piping that are of particular interest in considering its potential for use in residential
above-ground plumbing. The presentation is oriented to considerations of adequacy
of functional performance of plumbing systems from the user’s/owner’s viewpoint in
contrast with the typical product-specifications oriented format reflected in current
standards. Not only are the physical characteristics emphasized that relate most
directly to the determination of functional performance of installed systems, but the
importance of design and installation detail in the context is discussed. In conclusion,
this review indicates the need for better use of existing knowledge as well as for some
research and test development work particularly in the areas of thermal properties,
response to building fires, and resistance to water hammer.”

Manufacturers’ Information
1. IPEX, Inc., PlumbBetter – IPEX Piping Systems Installation Guide, Denver,
CO. The guide provides installation guidelines and product specifications regarding
thermal expansion, bending radius, cutting and joining instructions, firestop ratings, and
pressure drop and flow rate specifications. The document does not give guidance on
system design or layout, specifically stating that “the method of plumbing a residence or
commercial project is left to the discretion of the designer, contractor, or developer.”
2. REHAU, Inc. (2004). REHAU PEX Plumbing Systems – Technical Manual
855.620, Leesburg, VA. REHAU’s Techn cal Manual out nes a deta ed des gn
procedure for s ng a p umb ng d str but on system. Th s procedure is most l ke y to be
used by p umb ng des gn eng neers or fa y soph st cated trade contractors for larger,
more comp cated projects. It is not l ke y to be used by the major ty of resident
plumbing contractors or builders. The procedure described here could be used to
develop a more straightforward and user-friendly tool that would identify the optimum
distribution system design for a given situation.
3. Uponor Wirsbo, Inc. (1993). Aquapex Professional Plumbing Installation
Guide, Apple Valley, MN. Wirsbo’s installation guide gives detailed instruction about
installation of PEX tubing and manifolds, instructions for various types of connections
and required supports, and recommended distances from heat sources such as flues
or recessed light fixtures. The guide does show the different options for system design
including home-run, remote manifolds, modified home-run, and run-and-branch
systems. General advantages and limitations of the different systems are identified. The
guidance remains general except for a reference to a distance of approximately 12 to
15 feet from a central manifold as the maximum recommended for a home-run layout.
Demand or timed re-circulation is also mentioned as an energy and water saving design
feature. Wirsbo provides a detailed design and installation guide for their D’mand Hot
Water Delivery System.
4. Vanguard Piping Systems, Inc. (2005). Manabloc – Modular Manifold
Plumbing System for Use with Vanguard Vanex® SDR9 Cross-Linked
Polyethylene Tubing, McPherson, KS. This manual offers general design guidance for
parallel distribution systems using cross-linked polyethylene tubing. However, it does
not provide sufficiently specific information to allow a contractor to size and lay out
a distribution system for an entire project. Examples of the type of guidance given
include:
• Typical supply line size per number of bathrooms;
• Typical distribution line size per fixture flow requirement;
• Use of multiple manifolds when the home is large or there are a large number of
fixtures.
Understandably, the Manabloc manufacturer does not discuss advantages and
disadvantages of a parallel vs. tree distribution systems under different circumstances.
5. Viega North America, Pure Flow Water Systems – Installation Manual, Bedford,
MA. The manual provides detailed instructions for the installation of their Pexcel
and FostaPEX tubing. They outline different design and layout strategies in a general
manner. The manual also gives pressure drop information for their materials that could
be used to develop more specific design tools.
6. Zurn Industries, Inc., PEX Plumbing Design and Application Guide, Zurn
Industries, Inc., Erie, PA. The Zurn Guide offers similar installation instructions to
the other manufacturers. Each manufacturer recommends their specific crimp tool
and gauge. In addition to guidance regarding thermal expansion, protection from
damage, pressure drop, and flow rate, the Zurn manual also discusses sizing and
ocat ng man fo ds for para el p ng d str but on systems. Wh e deferr ng to loca
code requ rements, Zurn does recommend us ng 3 8- nch tub ng for hot water l nes
whenever poss e to reduce wa me, stat ng that 3 8- nch tub ng is usua y adequate
for most s nk, lavatory, and shower fixtures un ess the d stance is greater than 80 feet.
Appendix C – rESourCES
Plastics Pipe Institute (PPI) Technical Notes
1. TN-17 (Feb. 1998). “Crosslinked Polyethylene (PEX) Tubing.” This technical
note provides general information on cross-linked polyethylene (PEX), such as: “What
is PEX?” and “How does PEX improve properties of PE?” Three methods of crosslinking polyethylene to form PEX, qualification standards, and certification requirement
are presented. Finally, several applications for the use of PEX piping, and advantages of
PEX pipe systems are listed.
2. TN-26 (2002). “Erosion Study on Brass Insert Fittings Used in PEX Piping
Systems.” The objective of this test program was to subject different brass insert
fittings and different pipe diameters for PEX plumbing systems to flow rates that
represented the maximums that could occur if a plumbing system was sized according
to the 2000 Uniform Plumbing Code. Enough chlorinated water flowed through the
pipe and fittings equivalent to 40 years of service in a typical single family residence.
None of the brass fittings failed during the test. Weight losses were less than 3 percent
for all fittings. A test procedure is appended to this Technical Note.
3. TN-31 (2004). “Differences between PEX and PB Piping Systems for
Potable Water Applications.” Several features and properties of PEX pipe are
presented to differentiate between PEX and PB. Mechanical fittings are tested and
certified to comply with higher standards for chlorine resistance and long-term
durability than were used for polybutylene pipe.
4. TN-32 (2004). “UV Labeling Guidelines for PEX Pipes.” These guidelines
present recommendations for exposure and storage of PEX piping, and an example of a
cautionary label to be applied to packaging to ensure that PEX is not over exposed to
sunlight (UV radiation).
5. TN-33 (2004). “Standard Ultraviolet (UV) Radiation Exposure Method
for Crosslinked Polyethylene (PEX) Tubing.” This is an industry consensus
UV exposure test method that provides a definition of Total UV Energy per Monthly
Time Period, and requirements for PEX piping exposure. Reporting and recording
requirements are also presented.

GLoSSArY
ASTM: American Society for Testing and Materials
Corrosion: deterioration in metals caused by oxidation or chemical action
Cross-linked polyethylene: a flexible, “thermoset” plastic created using polymer technology
where the molecules of a high-density polyethylene (HDPE) base material are permanently
linked to each other by a process called cross-linking (PEX)
Elasticity: a measure of material stiffness or the ability of the material to stretch or deform
temporarily under a load
Fitting: a device or connection that allows the PEX pipe to change direction or size, such as a
tee, elbow, or coupling
Fixture: a device or appliance at the end of a water supply distribution pipe line. Example:
lavatory, water closet, tub/shower, dishwasher
Home-run: a plumbing design that utilizes a central manifold and distribution piping to each
hot and cold water fixture
IAPMO: International Association of Plumbing and Mechanical Officials
ICC: International Code Council
IPC: International Plumbing Code
IRC: International Residential Code
Joint: the connection of the PEX pipe to a fitting, fixture, or manifold
Manifold: a device having a series of ports that are used to connect distribution lines for
several fixtures
NSPC: National Standard Plumbing Code
Outlet: see fixture
pH: a sca e rang ng from 0 to 14 that ranks how acid c or a ka ne a l quid is; water w th a pH
be ow 7 is considered acid c and water w th a pH above 7 is considered a ka ne
Polybutylene: a “thermop ast c” po ymer that was used for supp y water p umb ng from
about 1978 to 1995. There were several reported failures; therefore, PB is no longer approved
for water supply piping (PB)
PPFA: Plastic Pipe and Fittings Association
PPI: Plastics Pipe Institute
Remote manifold: a plumbing system that uses trunk lines from the water source to small
manifolds at grouped fixtures, such as a bathroom; can be flow-through or closed end
Scaling: process of mineral buildup on the interior of a pipe
Test fixture: the tub-shower unit farthest from the water source that was instrumented to
measure flow rate, flowing pressure, and mixed water temperature in the lab tests
Thermoplastic: having the property of becoming soft when heated and hard when cooled
Thermoset: having the property of becoming permanently hard and rigid when heated or
cured
Trunk and branch: a plumbing design that has a large main line that feeds smaller pipes to
each fixture
Ultraviolet: high energy light waves found in sunlight that lead to the degradation of many
plastics and materials (UV)
UPC: Uniform Plumbing Code
Wait time: the time it takes for hot water to be delivered to the Test Fixture; delivery time
Water hammer: a banging noise heard in a water pipe following an abrupt alteration of the
flow with resultant pressure surges

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