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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Here’s links to a collection of our other blog posts about PLUMBING PIPES:

How can I protect my pipes to keep them from bursting during a hard winter freeze in North Florida?

Can galvanized steel pipe still be used for new water lines in a house? 

How can I tell if I have cast iron pipes in my house? 

Why can't a sanitary tee be used for a horizontal-to-horizontal drain pipe connection? 

What is the difference between green and white sewer drain pipes?

Is a washing machine drain hose required to be secured at the standpipe?

What are the abandoned pipes sticking out of the wall in my house?  

What are the code requirements for plumbing vent terminations?

What are the code requirements for layout of drain piping under sinks?

What causes a gurgling sound when a bathtub or sink drains? 

What is a "combination waste and vent" in a plumbing system? 

What is a building trap?  

What is a galvanized nipple?

What are the pipes sticking out near my water valves?

How do you accurately find a broken water pipe leak under the floor slab?

What is the difference between water pipe and sewage (waste) pipe?  

Is a hot water faucet handle required to be on the left? 

What is a dielectric union? 

What's that powdery crust on the pipe connections at the water heater? 

If all the plumbing drains have water in them and you can still smell sewer gas, what's causing the problem?  

How can I tell what type of plumbing pipe I have?

Why is there a flexible accordion pipe under the sink? 

What is the difference between PVC and ABS plumbing pipe?

What is the difference between water service pipe and water supply pipe? 

What are the pipes on my roof? 

• How can I find out what type of water pipe runs underground from the water meter to the house (service pipe)?

What is a P-trap?

Why is old galvanized steel water pipe a problem for homebuyers?

What does polybutylene pipe look like? Why is it a problem? 

• Which water pipes are an insurance problem and possibly uninsurable?

• Can you connect CPVC pipe directly to a gas water heater?  

     Visit our PLUMBING page for other related blog posts on this subject, or go to the INDEX for a complete listing of all our articles. 

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