Thread: Why no PVC

Why is PVC not allowed for use in the house for water distribution? I always forget to ask what the problems with it are, and my client asked me today.

PVC and ABS are not allowed for distribution as their max operating temp. are rated at 100 degrees. CPVC is rated for 180 degrees but has poor resistance to freezing. Thats all I could find.

I thought it would have something to do with the hot water. That makes sense.
Thanks.

IF THEY ARE USEING PVC, CHECK THE WATER HEATER T&P DRAIN. IT SHOULD BE "CPVC" TO PREVENT MELTING THE T&P DISCHARGE LINE.

OOPS; AND NOT REDUCED IN SIZE (3/4 INCH)

What I don't get is why you can use 180-degree rated CPVC on a T&P that doesn't blow off until 220 degrees.

I asked this same question to the county inspector a few months ago where I am in Portland Oregon and was told it is ok because it is not closed at the end and can run through the pipe. They did say it should be strapped every 3'

Originally Posted by Joshua Hardesty

What I don't get is why you can use 180-degree rated CPVC on a T&P that doesn't blow off until 220 degrees.

Because CPVC will resist greater than 180 degree water for longer than necessary for the cold water entering the water heater to cool the water down to less than 180 degrees.

As hot water discharges, that hot water is replaced with cold water from the cold water inlet, that lowers the temperature of the water in the tank, lowering the temperature further and further as the water continues to discharge through the T&P.

Adding to this is that this line is not "under pressure", even though the water coming out is "pressurized" (the T&P may discharge due to pressure, at 150 psi), the discharge line itself is open, limited in length, and limited in the number of elbows used - all to reduce the pressure loss across the pipe itself.

I believe I saw that CPVC is actually rated above 180 degrees. The actual rating concern is with the 100psi@180 degrees for use as TPR drain. Note the psi/temp rating.

It seems many inspectors have trouble with published limits. A pipe rated at 180 deg will not melt until it stays at a certain temperature for a given time period. This temperature is way over 180 deg.

Most, if not all, plastic piping systems for use in hot water distribution systems are tested to function for at least 48 hours (sometimes much longer) with conditions simulating a fully loaded T&P valve - 210F and 150 psi.

The pipes are not "rated" or "roll marked" for this, and we don't use them as such, but the testing is done to ensure it will function well enough under this unlikely circumstance.