Cross Linked Polyethethylene (PEX)

Cross Linked Polyethethylene, otherwise known as PEX, has become the new standard for water line installation in homes. Developed in Europe, this product was first used in the United States in 1984. To date, it has effectively replaced copper and PVC as the product of choice when installing potable water lines.

PEX Installation Practices & Issues

As with any new product, sometimes there are issues with the installation practices. We have seen this product used to supply gas water heaters. While acceptable, the manufacturer clearly states that it cannot be installed next to a gas water heater flue. This flue becomes very hot and may actually damage the PEX. The manufacturer states that PEX needs at least an 18” copper line installed from the tank and then connected to the PEX lines, away from the heat of the flue. A water leak on a pressurized supply line in the attic, where most water heaters are installed here, could lead to extensive water damage to the interior of the home. Also, the Uniform Plumbing Code 604.11.2 states “PEX tubing shall not be installed within the first eighteen (18) inches (457mm) of piping connected to a water heater.” I have seen the supply plumbing lines installed correctly, but the TPR line installed directly next to the water heater, next to the hot water heater flue. The code and manufacturer’s specifications appear to prohibit this type of installation.

Uninsulated PEX Installation

Another installation practice that has gained ground here in the south is the installation of uninsulated PEX in unconditioned spaces. For instance, it is not uncommon to walk into an attic and find blue and red supply lines lying on top of the blown insulation without any freeze protection. I have actually had plumbers write me letters stating that PEX lines do not need freeze protection because they will not break. Unfortunately, they are right about the lines not breaking, but make no mistake, PEX lines will freeze. Ask the family who had no water to their interior fixtures because all of the PEX water lines froze solid during a recent freeze. The manufacturer’s specifications clearly say that the product is freeze resistant: “While freezing conditions often cause copper and CPVC pipe to break or burst, causing thousands of dollars in water damage, PEX tubing will expand several times its original size without damage. However, it is recommended that you follow all codes regarding water line freeze prevention.” (www.apolloflow.com)

Installation of PEX in Direct Sunlight

Also, when PEX is installed outside it is susceptible to damage from ultraviolet rays. The manufacturer states that it should be kept out of direct sunlight. If you walk around your home, you may find a blue or red tube protruding from the base of the wall, normally in close proximity of the water heater. This may be the drip line connected to the water heater pressure release valve. This valve will release and discharge water should the water heater malfunction. If the tubing deteriorates because of exposure to direct sunlight, it may detach from the elbow and pull back into the wall cavity. Should the water heater discharge water through the pressure release valve, water damage to the interior of the wall cavity will occur. Unfortunately this scenario will not occur for many years, long past the installers warranty. We tell our clients to simply place a PVC elbow over the existing elbow, so that it completely covers the PEX. The elbow can be secured in place with silicon caulk. This is a cheap remedy that could avert costly moisture damage down the road.

If you are unsure about PEX installation in your home, hire a local home inspector to come and evaluate the lines and make recommendations.