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Why can't PVC be used for water pipe inside a house?
Friday, July 27, 2018
Both the International Residential Code (IRC) and the Florida Building Code (FBC) do not have PVC (polyvinyl chloride) pipe on their list of approved water distribution pipe. The building codes make a distinction between water “service” pipe, which means pipe that delivers water to the house, and water “distribution” pipe, which is the pipe inside a house that runs to the plumbing fixtures. Pipe changes from the supply to distribution category once it enters the house and, although PVC is rated for service pipe, it is not rated for distribution.
The reason for not allowing PVC for distribution pipe is that it is not rated to withstand the thermal expansion stress caused by hot water. Even cold water pipe inside a home can end up with hot water in it, because the heat inside a water heater transfers backward through the water in the cold water supply pipe. If you wrapped your hands around both the hot and cold pipes at the top of a water heater, it would difficult to tell them apart based on their temperature near where they penetrate the tank.
But PVC can be used inside the home as drain pipe (also called DWV for drain-waste-vent, which is only under atmospheric pressure), draining the condensate water created by an air conditioning air handler, dryer exhaust venting, and as a flue vent for high-efficiency gas furnaces.
PVC is not allowed to be used for the discharge piping from the TPR valve of a water heater, which opens to release super-hot water from a water heater when the thermostat fails and overheats the tank. The pipe begins to sag and collapse when extremely hot water flows through it.
A plastic pipe with a slightly different chemical formulation and similar name, CPVC (chlorinated polyvinyl chloride, shown above), should not be confused with PVC when talking about water pipe. CPVC is rated for distribution pipe and hot water. It is a cream-color plastic, whereas PVC is white.
Also, see our blog post Are plastic pipes (PVC, CPVC, and PEX) safe for drinking water?
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