Using PEX tubing as an alternative to copper pipe has become increasingly common over the last decade. It has become especially popular with remodelers because it can be fished through finished walls, floors and ceilings much as an electric wire or cable is fished through finished structures. The ability to fish the tubing through walls, floors and ceilings minimizes the amount of damage done during the remodeling process.
The 2012 National Standard Plumbing Code, or NSPC, and all local plumbing codes require all PEX plumbing installations be pressure tested. All local codes require PEX installation test out to the minimum standards set down in the National Standard Plumbing Code, but many local codes have requirements that exceed the minimum. PEX systems may be pressure tested using either water or air pressure.
Pressure testing a PEX plumbing system requires at least a minimum pressure of 40 psi with a maximum pressure of 125 psi be applied to the system. The most common pressure used in air testing for leaks is 100 psi. Apply the test pressure for at least 15 minutes; you should not lose more than 8 psi over a 60-minute period of time. A loss of 8 psi during the initial hour is considered normal, and is caused by the normal deformation of the new tubing. A loss of more than 8 psi indicates the presence of leaks within the system.
When water testing a PEX system, the water pressure should be at least equal to the normal operating pressure. Under no circumstances should the water pressure be less than 40 psi or more than 225 psi. Just as with air-pressure testing, the duration of the applied pressure test must be at least 15 minutes. Since plumbing codes permit water testing at the system's normal operating pressure, as long as that pressure is 40 psi or higher, the water test probably is the method of choice for a homeowner. The problem with water testing at normal operating pressure is that some microscopic leaks can go undetected. Microscopic leaks may not be a problem at first, but can become a problem over time.
Leak Detector Solution
Leaks are much easier to detect when you use a detector solution. Although commercial solutions are available, you can mix up your own for a fraction of the cost. Make a leak detection solution by mixing 2 ounces of a major brand of dish-washing detergent to every 1 gallon of water used to fill the closed PEX system.