Cross-linked polyethylene (PEX) tubing is a plastic material used for water supply piping systems. The product offers several advantages over copper, PVC, and galvanized steel plumbing pipes. PEX is flexible and easier to install than a rigid pipe, and it offers high heat-resistance and long-term durability. PEX comes in sizes from 1/4 inch to 4 inches in diameter. The most commonly used sizes for water supply piping are 1/2, 3/4, and 1 inch.
PEX Plumbing Pipe Advantages
PEX plumbing pipe offers several advantages over traditional plumbing pipe materials. Because it is made with a flexible and resilient material, PEX is more resistant to breakage caused by freezing than both copper or PVC pipe. Flexibility also makes PEX easier to install. PEX tubing can be bent and can curve around structural framing and other obstacles, reducing the need for holes and notches to accommodate the tubing. Bends in the tubing also eliminate the need for many elbows and other transition fittings, saving both cost and installation time. In other words, you can wind PEX throughout the walls and floors with a continuous, uninterrupted pipe to its final connection.
PEX conserves energy by reducing heat transfer, or loss of heat through the pipe wall. By contrast, metal pipes are particularly prone to heat loss. PEX also doesn't corrode—another advantage over metal pipe especially galvanized steel pipe, which consistently corrodes over time. Compared to copper, PEX is more resistant to scale buildup and the resulting loss of flow through the pipe. Also, PEX is much less expensive than copper pipe.
For amateur installers, perhaps the best advantage of PEX is that it does not require soldered connections (like a copper pipe) or tricky threaded connections (like galvanized steel). PEX also requires fewer connections and fittings overall, which helps to lower costs and decreases the chances of leaks. Typically, PEX can be installed more quickly than any other plumbing pipe used for water supply.
Applications for PEX Plumbing Pipe
PEX plumbing pipe was developed in the 1960s and is accepted by all major plumbing and building codes in the U.S. However, local codes, which are the law in any area, may have specific requirements or restrictions for PEX installations.
The standard method for installing PEX tubing is to join it with barbed fittings and special metal crimp rings that are secured using a crimp tool. Once the ring is crimped in place, the installer checks it with a "go/no go" tool that confirms the proper diameter of the crimped ring. PEX can also be installed with DIY-friendly push-in fittings. PEX tubing is easy to cut with a PEX tubing cutter.
In general, PEX piping can be used for:
- Water supply lines or portable distribution systems
- Radiant floor heating applications
- Heat transfer applications, such as floor cooling, snow melting, and permafrost protection
- Water distribution for hot water applications, including radiators
- Residential fire/sprinkler systems
Limitations of PEX Tubing
PEX tubing must be installed only in approved locations where it is protected from damage. It must be kept away from contact with flame or extreme heat, and it must not be exposed to direct or indirect UV light, which damages the pipe material over time. PEX also can be damaged by high concentrations of chlorine.
Do not install PEX in contaminated soils, and do not use pipe thread compounds or mineral- or oil-based products, as these materials can alter the pipe’s characteristics and can damage the pipe fittings. PEX is not approved for installation near hazardous waste disposal sites or petroleum storage tanks.
Labeling on PEX Tubing
PEX tubing is manufactured and classified by its outside diameter dimension, commonly called copper tube size (CTS). PEX pipes should be labeled, at least every 5 feet, with the following information:
- Pipe manufacturer name or trademark
- Pipe standard to which it conforms (ASTM F876, F877, AWWA C904 or CSA B137.5)
- Tube size and copper tube size (CTS)
- Plumbing pipe designation code (PEX0006 or similar)
- Pipe specified pressure/temperature rating(s)
- SDR9 (Standard Dimension Ratio is a ratio of the pipe's diameter to the wall thickness of the pipe; it is used by manufacturers to rate pressure piping)
- Pipe intended for potable water must be marked as suitable for this application
- ASTM fittings designations approved for use by the pipe manufacturer