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As we know them, plastics are polymers that usually include petroleum. Because many green initiatives encourage us to reduce our use of petroleum products, plastic plumbing pipe may seem out of place in a list of environment-friendly materials. Compared to the total costs of using copper, however, materials such as polypropylene and cross-linked polyethylene (PEX) become much more attractive, with benefits that traditional materials do not offer.
Two polymers currently in use for water supply lines are PEX and polypropylene. PEX resists extreme temperatures and handles most liquids without reaction, which makes it a smart choice for indoor plumbing. Unlike traditional copper pipe, PEX can bend to follow
curves and work around corners. Polypropylene provides many of the same benefits as PEX, and is recyclable as well.
One polymer used in plumbing pipe, polyvinyl chloride (PVC), is associated with environmental harm. Water mains made with PVC before 1977 contain high levels of vinyl chloride monomer, a toxic chemical known to be a carcinogen. Newer PVC pipes contain lower levels of harmful compounds, but the manufacturing of PVC still produces dioxins, and the use of PVC in plumbing is generally restricted to drain lines.
Both polyethylene and polypropylene are made without chlorine, bromine, or other harmful chemicals. They are considered benign plastics.
About PEX
PEX is a form of polyethylene in which the molecules are cross-linked to increase strength and durability without sacrificing flexibility. This makes it easy to install, but difficult or impossible to recycle. Still, PEX offers sufficient environmental benefits to be considered a green alternative to copper pipe. Even as polypropylene pipe becomes more common in the United States, PEX will remain a viable option, thanks to its ease of use and low cost.
Since the 1960s, PEX has been used in plumbing and radiant heating systems in Europe. It was first introduced in the United States in the 1980s, and its use has grown steadily since then. It’s flexible in more than one way; because PEX handles water at all temperatures
from just above boiling to just below freezing, it is suitable for use in home plumbing, service lines, hydronic heating systems, and snowmelting applications.
In home plumbing, PEX can be routed much more easily than copper pipe. This makes remodeling projects far simpler, because it can be worked around other systems such as drain lines, gas pipes, electrical conduit, and so on. Because PEX can curve and bend, it
requires fewer joints, which reduces the potential for leaks.
The inside diameter of PEX pipe is relatively small, but it has a low coefficient of drag. This means liquids flow smoothly through it without leaving mineral deposits, and less standing water is left in the pipes, so you can adjust faucet temperatures more quickly. PEX is also quieter than copper pipes.
Finding and Buying PEX
Thanks to its growing popularity, PEX is now available through many retail building supply stores. If the retailers closest to you don’t carry PEX, look for a plumbing supply wholesaler, who may be willing to sell directly to you—even if you don’t have a contractor’s license. The
same seller who carries PEX pipe should also be able to provide the fittings you need.
Sizes from ¼ inch to 1 inch are common; larger diameters are available, but most of the time only as special-order items. The sizes of PEX pipe are given in copper tube size (CTS) numbers, based on the sizes of comparable copper tubing. All sizes should have the same
pressure ratings, because the wall thickness is proportionate to the diameter.
Shorter lengths are sold as straight pipes up to 20 feet long, while coils of up to 1000 feet provide enough length for many separate lines. Some manufacturers color hot and cold lines differently; make sure the pipe you buy is rated for its intended use.
Using PEX
From lower material costs to easier installations to reduced maintenance, PEX can help you save money, time, and effort. If you install a manifold at the source, with cold lines running directly from the municipal water supply and hot lines from the water heater, you can set up separate water lines for each room—or even each fixture. This “home run” configuration brings hot water to the fixtures more quickly, saving both water and the energy used to heat it.
Speaking of heat, you can use PEX for hydronic systems. It can be encased in concrete for use as part of an in-floor heating system. Its flexibility allows you to create a single, continuous loop of pipe with no joints or connectors. At the other end of the thermometer, you can run very cold water through PEX pipe; just don’t use it for outdoor lines above ground. Exposure to direct sunlight and severe weather can shorten the life of PEX pipe.
To connect separate pieces of PEX, installers use mechanical insert fittings, either crimp style or compression fittings. In part because of its resistance to friction, PEX should not be fastened with glue or heat. For a list of approved connectors, check with the manufacturer or review the standards ASTM F 1807 and ASTM F 1960. One advantage of mechanical fittings is that you can test them immediately, without waiting for solder to cool or glue to dry.
Before you specify or install PEX as plumbing pipe, check your local building codes. If you need to provide evidence that PEX is safe for use in home plumbing, you’ll have plenty of support. It conforms to the standards ASTM F 876 and F 877, AWWA C904, and CSA B137.5. Polyethylene pipe has been tested and approved by ASTM, ANSI/NSF International, and CSA, and all major model plumbing codes used in the United States and Canada; NPC, UPC, IPC, and NSPC.
About Polypropylene
While water from polyethylene pipe is safe to drink, some people say it imparts a taste they notice and dislike. Polypropylene pipe, on the other hand, does not contain the chemical stabilizers that are common in polyethylene. Its chief advantage over polyethylene, though,
is not how it’s made but that it can be recycled.
The same properties that make PEX pipe a worthy choice are also true of polypropylene. It’s flexible, economical, and easy to install, and it does not react to common household chemicals. Like polyethylene, polypropylene has a low coefficient of friction so fluid moves easily through it, and it’s slow to conduct heat, which means the water temperature won’t change much in transit. Watch for polypropylene pipe to become more common in the next few years.
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