PEX Information

PEX Information Everything you need to know about plumbing with PEX

Crosslinking is a chemical reaction that occurs between polyethylene polymer chains. Crosslinking causes the HDPE to become stronger and resistant to cold temperature cracking or brittleness on impact while retaining its flexibility. The three methods of crosslinking HDPE are the Engels method (PEX-a), the Silane Method (PEX-b), and the Radiation method (PEX-c). Several industry participants claim that the PEX-a method yield more flexible tubing than the other methods. All three types of PEX tubing meet the ASTM, NSF and CSA standards.

PEX plumbing, PEX fittings, PEX tools Contents

PEX tubing is made from crosslinked HDPE (high density polyethylene) polymer. The HDPE is melted and continuously extruded into tube. The crosslinking of the HDPE is accomplished in one of three different methods.

PEX plumbing has been in use in Europe since about 1970, and was introduced in the U.S. around 1980. The use of PEX has been increasing ever since, replacing copper pipe in many applications, especially radiant heating systems installed in the slab under floors or walkways. Interest in PEX for hot and cold water plumbing has increased recently in the United States.

Advantages of PEX Plumbing

• Flexible PEX tube is manufactured by extrusion, and shipped and stored on spools, where rigid plastic or metal piping must be cut to some practical length for shipping and storage. This leads to several advantages, including lower shipping and handling costs due to decreased weight and improved storage options.
• PEX plumbing installations require fewer fittings than rigid piping. The flexible tubing can turn 90 degree corners without the need for elbow fittings, and PEX tubing unrolled from spools can be installed in long runs without the need for coupling fittings.
• Attaching PEX tube to fittings does not require soldering, and so eliminates the health hazards involved with lead-based solder and acid fluxes, PEX is also safer to install since a torch is not needed to make connections..
• PEX resists the scale build-up common with copper pipe, and does not pit or corrode when exposed to acidic water.
• PEX is much more resistant to freeze-breakage than copper or rigid plastic pipe.
• PEX tubing does not transfer heat as readily as copper, and so conserves energy.
• Water flows more quietly through PEX tube, and the characteristic "water hammer" noise of copper pipe systems is virtually eliminated.
• PEX plumbing installations cost less because:
  • PEX is less expensive than copper pipe.
  • Less time is spent running pipe and installing fittings than with rigid pipe systems.
  • Installing fewer fittings reduces the chances for expensive callbacks.

Oxygen Barriers

Some applications require PEX with added oxygen barrier properties. Radiant floor heating (or hydronic heating systems) may include some ferrous (iron-containing) components which will corrode over time if exposed to oxygen. Since standard PEX tubing allows some oxygen to penetrate through the tube walls, various "Oxygen Barrier PEX" tubing has been designed to prevent diffusion of oxygen into these systems. Two types of specialty PEX pipe are offered:

1. Oxygen barrier PEX has a layer of polymer laminated to the outside surface (or sandwiched internally between PEX layers) that prevents oxygen from penetrating. The polymer film is usually EVOH (ethyl vinyl alcohol copolymer), used in the food industry as an oxygen barrier.

2. PEX-Al-PEX (or PEX-Aluminum-PEX or "PAP") is a specialty PEX tubing manufactured by several suppliers. This tubing has a layer of aluminum embedded between layers of PEX to provide an oxygen barrier. PEX-Al-PEX may also be called multilayer pipe or composite plastic aluminum pipe. PEX-Al-PEX will also retain shape when bent, and may also exhibit less expansion and shrinkage during temperature fluctuations, but may be less flexible than PEX tubing. PEX-AL-PEX costs about 30% more than standard PEX.

PEX Tubing

The terms PEX pipe and PEX tube have been used interchangeably, however some manufacturers distinguish beween the two by manufacturing to different inside/outside diameters. For example, PEX pipe may be manufactured to IPS-ID (iron pipe size, inside diameter controlled) sizes with varying thickness to meet pressure requirements, while PEX tube may be manufactured to CTS-OD (copper tubing size, outside diameter controlled) sizes, commonly with a standard thickness of SDR-9 (standard dimension ratio).

The PEX tube manufactured to CTS-OD sizes is the most common, with available sizes including 3/8", 1/2", 5/8", 3/4" and 1". On this website, ",PEX tube", refers to this common CTS-OD product.

Before extrusion, the HDPE can be pigmented to yield color-coded pipe. Common PEX tubing colors are "natural" (hazy clear, unpigmented), white, black, red and blue. The red and blue colors are used to help plumbers and homeowners distinguish between hot and cold water supply lines. The tube will be marked on the outside to show which standards it meets.

As it is produced, PEX is wound onto spools for storage and shipping. A typical spool of 1/2 inch PEX will hold 1200 feet of tubing.

PEX connection methods Standard Connection Method

The standard method for connecting PEX pipe to brass PEX fittings uses a copper crimp ring and a PEX crimping tool. The copper crimp ring is inserted over the pipe, the fitting is inserted inside the pipe, and the copper ring is crimped over the pipe and fitting using the PEX crimping tool. Tools, fittings and crimp rings are available from several suppliers. Information about testing standards for this method can be found on the ASTM standards page.

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