PVC or ABS plastic piping is often used on high-efficiency heating and water heating systems as vent piping for the exhaust gases, since the exhaust temperatures are relatively low. This piping is often vented out the side of the home.
There are different types of piping used, and one style commonly used is called ‘Cellular-Core” PVC. This type of piping differs from solid PVC or ABS as it has a core built into the walls of the pipe. This makes the piping cheaper and lighter, but slightly less rigid than it’s solid counterpart. Recently, municipalities and many material manufacturers are no longer allowing cellular core piping (PVC and ABS) for new installations on exhaust ventilation applications due to concerns that have developed in certain installations.
The issue arises with the piping when it is used as an exhaust vent for mechanical items. This includes high-efficiency furnaces, boilers, and water heaters. The higher temperatures of the exhaust can distort the interior core of the piping and fittings which can cause holes or cracking after prolonged exposure. Cracking or warping of exhaust pipes can lead to a larger safety issue where an appliance could vent carbon monoxide into the living area of a home. For this reason, some municipalities are not allowing Cellular Core PVC or ABS to be used for venting applications.