View the ToolBase TechSpecs- Home-Run Plumbing Systems for an overview of this technology.
Do you want a water supply piping system that doesn’t corrode or develop pinhole leaks, is chlorine-resistant, scale-resistant, and has fewer fittings, connections, and elbows than rigid plastic and metallic pipe? Then you need to explore the use of cross-linked polyethylene (PEX) for your next water supply piping installation.
Cross-linked polyethylene (PEX) is a high-temperature, flexible plastic (polymer) pipe. The cross-linking raises the thermal stability of the material under load. Thus, the resistance to environmental stress cracking, creep, and slow crack growth are greatly improved over polyethylene.
PEX pipe is approved for potable hot- and cold-water plumbing systems and hot-water (hydronic) heating systems in all model plumbing and mechanical codes across the U.S. and Canada. PEX piping systems are durable, provide security for safe drinking water, and use reliable connections and fittings. There are currently about ten domestic producers of quality PEX piping.
Brass fittings and couplings and polyethylene tees and elbows are available. Fittings are available in both mechanical compression and crimping styles, depending on application and manufacturer. In addition to domestic water supply systems, PEX tubing can be used for floor or wall radiant heating, and snow and ice melting systems in sidewalks and driveways.
PEX tubing is light weight, and it can withstand operating temperatures of up to 200° F (93° C). It is flexible and can easily be bent around corners and obstacles, and through floor systems. Sizes of PEX tubing range from 3/8-inch to over 2 inches.
For more information, see Cross-Linked Polyethylene PEX in Residential Plumbing Systems. This TechNote details the differences and similarities between three PEX system designs established by laboratory testing performed at the NAHB Research Center. The Copper Pinhole Leaks TechNote describes a significant problem with copper piping that is not present in PEX installations.
More about PEX is available in these online videos.
In parallel layouts where supply lines are dedicated to one fixture, only two fittings are used. Labor costs can be lower than rigid piping system installations.
There is less heat loss from PEX than there is from metallic pipe. The small diameter tubing that can be used in parallel installations allows less water consumption waiting for delivery of the heated water.
Polyethylene has no VOCs and can be recycled.
Successfully used in Europe and the U.S. for over 30 years. Extensive testing and certification is conducted to assure durability and resistance to effects of high and low temperatures and chlorine.
It is relatively easy for builders and plumbers to transition to PEX piping. Additional training will be needed for installers to learn the layout, pipe support spacing, and connection methods with the new system. Specialized tools are required to cut the tubing, install connections, and check the tightness of crimped connections. Designers can layout PEX in a traditional tree and branch arrangement, or other hybrid systems such as homerun or remote manifold. These other systems have the potential save additional time and money.
Cost of home-run plumbing system materials are often less than similar rigid pipe systems. Cost will depend on the system design, house size, distributor, and product availability. May require added training time/learning curve and design time for trades.
PEX systems can reduce maintenance and repair costs because systems that are installed in parallel have fewer connections which are typically more accessible than tree/branch installations. They also can contribute to hot water energy savings, which can reduce utility bills.
PEX piping is approved in all the major building codes, but has not received local code acceptance in some areas of the country. PEX tubing must comply with ASTM F876, “Specification for Cross-Linked Polyethylene (PEX) Tubing,” and ASTM F877, "Specification for Cross-linked Polyethylene (PEX) Plastic Hot and Cold Water Distribution Systems." Section P2903.8 of the 2003 International Residential Code (IRC) covers Parallel Water-Distribution System Manifolds, and includes sizing, valves, distribution lines, and support. Section P2904 covers materials, joints, and connections.
Brighton Construction at Liberty Village: Lincoln, NE
- Capture installation time and material cost of PEX and copper supply water systems so that builders can benchmark their potential success with new technologies. The performance of each system will also be determined based on flow rates at the fixtures and delivery time of hot water
- Five houses were studied to determine installation time and cost of a parallel PEX water supply piping system versus a conventional trunk and branch copper system.
- Three houses included the PEX system and two included a copper system.
- Water use of each system was captured before occupancy to determine fixture flow rates and the delivery time for hot water to reach the fixtures.
- Intial report is available: Field Results: Evaluation of Residential Water Distribution Piping Installation (Task 1)
Denver, Colorado, Oakwood Homes (PATH Demonstration Site)
- Production builder of move-up homes implemented PEX and plastic plumbing manifold
- The installed cost to the builder was about five percent less than copper.
- Open-web floor joists facilitated installation of PEX and other technologies
- Installed waste and vent pipe prior to PEX installation to avoid damage to PEX from chemical welding
- Flushed main street line of sand and dirt before running water through manifold to prevent damage; installed valve upstream of manifold for this purpose
- To ease overhead work, plumbers used stilts commonly used by drywall contractors
Freehold, New Jersey, K. Hovnanian (2002 PATH Field Evaluation)
- Production builder incorporated several advanced technologies in its “Idea House.” System was hybrid copper/PEX
- Savings were approximately $200 versus conventional copper
- Plumbers did not like transitioning between copper and PEX in this hybrid system; however, they agreed that system can save installation time
- Code officials reluctant to allow this technology
- Learned to unroll the tubing before pulling through walls to prevent kinking; pulling tubing may require two workers—one to push, one to pull
- Other lessons learned – tubing tends to become stiff in cold weather; crimping tool can become cumbersome in tight spaces
Philadelphia, Pennsylvania, Model reMODEL (1999 PATH Field Evaluation)
Remodel of a Philadelphia row home demonstrating numerous technologies including a home run plumbing manifold with PEX piping
- Cost savings was $1000, of which $960 was attributed to labor, compared to conventional copper pipe
- PEX plumbing system installation took 17 hours versus 33 hours to install copper piping
Home-run systems can take significantly less time to install than traditional rigid pipe plumbing systems once the learning curve has been overcome.
- Trades need to receive training in proper handling and installation
- Requires some specialized tools
- Special care required to eliminate construction and line debris from sensitive manifolds
Manufacturers typically offer a 10-year limited warranty on the manifold, piping, and fittings.
PEX installation can save labor and materials and be cost competitive with rigid pipe systems. Because PEX piping will not corrode and resists scale buildup, maintenance costs may be lower than rigid piping. Fewer leaks are possible because fewer connections can be used. Three-eighths inch diameter PEX piping can reduce hot water delivery time by up to 18% over one-half inch copper piping.
PEX tubing should not connect directly to a hot water tank or solar water heater where the temperature of the water could exceed 200° F. Fittings and connections must be installed with special calibrated tools by a trained plumber. The pipe should not be used in installations subject to continual ultraviolet light exposure.