Plastic TPRV line?

What do you think?


If it’s cpvc, then it’s fine. Basic pvc (waste pipe) isn’t rated for that amount of heat and could potentially melt.

It’s about strength, not heat.
Is Sch 40 stronger than CPVC?
It’s much bigger. Does C make up the strength differance of PVC?

I’m seeing more and more PTR valves getting piped with CPVC nowadays.

I stopped calling them out.

The use of CPVC is well explained in this Manual.

Might come in handy for some.

Marcel :slight_smile: :smiley:

Thanks, Marcel!

It says it is usable in TPR applications (even though it is only rated for 100# @ 180F sustained; TPR discharge temp. and pressure can exceed this easily) , but my point that CPVC is “copper sized” piping, there is less capacity for flow and the more fittings/length used that greater the pressure at TPR discharge. TPR valve piping should not be smaller than the the TPR size.

Anyway, I see PVC/CPVC used all the time for TPR diverter tubing.
I guess it prevents a “missing” pipe when your kids pawn the copper! :slight_smile:

The keyword here seems to be ‘sustained’. The relief lifts, there should be no pressure(other than back pressure) since the piping is open to atmosphere. The pressure in the tank will be used as a motive force, not as hydrostatic force. Also temperature will not remain >180F. (not going into a mollier’s diagram, for you geeks). So considering the only driving force is the wh itself, once opened to atmosphere, the WH will be exhausted. Enven at the worse case the tprv sticks open, the motve force will be the water supply(40-80#, 55F?).


There is a listed, plastic pipe (other than CPVC or PVC) made specifically for this application. The fitting in your picture makes me believe that’s what this is. The markings on the pipe will tell you for sure.

PVC is not approved for this use, but CPVC is.

Strength is not an issue with a TPRV piping, it is open, so there is not any pressure build up, only heat.

Technically, neither strength nor heat-resistance is at issue. “Listed and approved materials” is the issue.

There are many different types of materials that are strong enough, and/or heat-resistant enough to serve as TPR discharge piping, but only specific materials are listed and/or approved for the application.

Interesting topic. I had a discussion with a plumber friend of mine on this same issue and was told that copper is the only material which should be used for the discharge line. I told him that I read from many different sources that CPVC was OK to use. He of course denied this as he can probably get more money installing copper pipe than CPVC.

Let the conversation continue. Off to some marketing stuff and see the Realtors.

The Uniform Plumbing Code is very clear. . .

UPC 608.5 Relief valves located inside a building shall be provided with a drain, not smaller than the relief valve outlet, of galvanized steel, hard drawn copper piping and fittings, CPVC, or listed relief valve drain tube. . .

I’ve even seen PEX being used (and according to a phone conversation with a PEX representative, also approved.)

Code calls for rigid pipe and CPVC is approved, but to my knowledge no other plastic. You don’t have to use copper, you can use galvanized. I personally don’t like to see plastic because the heat from the water will loosen the threads over a period of time. This causes the adapter to loosen where it enters the TPR valve. There was a thread here a few weeks ago that went over all of this. No PEX. the ID (inside diameter) of 3/4" PEX fitting is not 3/4".

The PEX fittings are not full size. 3/4" PEX is 3/4" ID, but the fittings aren’t. I don’t like to see any plastic, but CPVC is approved in most jurisdictions. Since copper is expensive a 4’ piece of 3/4" galvanized threaded one end could be used. Of course, what I don’t like doesn’t really matter.

Below is from an old thread

PEX is on the list of acceptable materials for the TPR discharge.

The requirements for pipe material are at IRC P2803.6.1: “Be constructed of those materials listed in Section P2904.5 or materials tested, rated and approved for such use in accordance with ASME A112.4.1.”

A screen shot of the table is attached, and PEX is on the list. (Think about it, if PEX is suitable for distribution of hot water, why not as a discharge for it? About the fittings, don’t they withstand all the pressure in the system under normal conditions and wouldn’t you think there is a pretty high safety factor built in? I don’t know the limitations on the fittings, but the table seems to be clear.)