PEX Plumbing Pipe

PEX Pipe: The New Alternative for Plumbing Installations

Radiant heating system manifold using PEX tubing
••• Chixoy/Wikimedia Commons/GFDL, License migration redundant, Self-published work CC BY-SA 3.0

PEX tubing is made of cross-linked polyethylene. It is a plastic material used for water supply piping systems and offers several advantages over copper, PVC, and galvanized steel plumbing pipes. PEX is flexible and easier to install than 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.

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 resulting loss of flow through the pipe. 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 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 for leaks. Typically, PEX can be installed more quickly than any other plumbing pipe.

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 US. However, local codes (which are the law in any area) may have specific requirements or restrictions on the use of PEX.

In general, PEX piping can be used for:

  • Water supply lines or potable distribution systems
  • Plumbing and 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 that protect it 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 or damage 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 and/or CSA B137.5)
  • Tube size and copper tube size
  • 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)
  • If pipe is intended for potable water, it must be marked for suitability
  • ASTM fittings designations approved for use by the pipe manufacturer