TPR Discharge with Pex fittings

[JB Thompson]

I see Pex fittings used to elbow the termination all the time and write it up based on reducing the size of the discharge pipe, but I have scanned numerous forums and articles on the internet and cannot find mention of it.

To make sure I am understanding it and that I am not writing up something that really is correct...

Anything, that reduces the interior diameter of the pipe is a violation of 2804.6.1. Right?

3. )Not be smaller than the diameter of the outlet of
the valve served and shall discharge full size to the
air gap.

Secondly, if I am reading #14 properly, if the valve is 3/4", then the Pex should be 1". Correct?

14. Be one nominal size larger than the size of the
relief-valve outlet, where the relief-valve discharge
piping is constructed of PEX or PE-RT tubing.
The outlet end of such tubing shall be fastened
in place.

Also, do any of you ever see the termination fastened in place?

Just wanting to do a good job here. Thanks, Bruce.

[Jerry Peck]

The key is in the wording ... all pipe sizes are "nominal" ... bet you haven't seen a 2x4 lately either ... :)

Think of CPVC ... it is quite a bit smaller in actual dimensions - but it is still 1/2" and 3/4" "nominal".

PEX is permitted as the T&P relief valve discharge pipe.

[JB Thompson]

The key is in the wording ... all pipe sizes are "nominal" ... bet you haven't seen a 2x4 lately either ... :)

Think of CPVC ... it is quite a bit smaller in actual dimensions - but it is still 1/2" and 3/4" "nominal".

PEX is permitted as the T&P relief valve discharge pipe.

I've understood that PEX is permitted and based on what you're saying about "nominal" (at least I think I understand where you're going with this), then the fittings which are physically smaller ARE permitted....assuming they are 3/4" nominal.

Is that what you're saying?

[Jim Luttrall]

14. Be one nominal size larger than the size of the
relief-valve outlet, where the relief-valve discharge
piping is constructed of PEX or PE-RT tubing.
The outlet end of such tubing shall be fastened
in place.
Where are you getting this from?
Everything I read stops at #13

[Jerry Peck]

... then the fittings which are physically smaller ARE permitted....assuming they are 3/4" nominal.

Is that what you're saying?

Precisely what I am saying. :)

The inside diameter of the piping varies even within copper types, soft drawn, hard drawn, and annealed - it is the outside diameter which remains constant so they all fit the same fittings.

The inside diameter of PVC is even smaller (walls are thicker) and CPVC is even smaller than PVC (even the outside diameter is smaller), yet all the different types have the same IP (iron pipe) sized threaded fittings, 3/8", 1/2", 3/4", etc. ... so let's consider the inside diameter of iron pipe with the same thread fitting size - the walls of iron pipe are thicker than almost any other pipe, except maybe PVC, and 3/4" CPVC looks like it could almost fit inside of 3/4" hard drawn cooper ... all the same nominal size and all fit and thread into the same threaded fittings.

[JB Thompson]

Where are you getting this from?
Everything I read stops at #13

2015 IRC

- - - Updated - - -


Precisely what I am saying. :)

The inside diameter of the piping varies even within copper types, soft drawn, hard drawn, and annealed - it is the outside diameter which remains constant so they all fit the same fittings.

The inside diameter of PVC is even smaller (walls are thicker) and CPVC is even smaller than PVC (even the outside diameter is smaller), yet all the different types have the same IP (iron pipe) sized threaded fittings, 3/8", 1/2", 3/4", etc. ... so let's consider the inside diameter of iron pipe with the same thread fitting size - the walls of iron pipe are thicker than almost any other pipe, except maybe PVC, and 3/4" CPVC looks like it could almost fit inside of 3/4" hard drawn cooper ... all the same nominal size and all fit and thread into the same threaded fittings.

I've always understood the O.D. and I.D. differences, but apparently I've never grasped the word "nominal". Thanks for the clarification.

[Jerry Peck]

2015 IRC.

The best thing that new section does is provide a stated requirement to anchor the end of the PEX ... I have used the spacing of supports in the past.

The worst thing that new section does is ignore the fact that there are other piping types which are even smaller than PEX - such as CPVC (the end of which also needs to be anchored).

[Jim Luttrall]

I had not seen the requirement of
upsizing of PEX and securing the end.

Of course I almost never see PEX on TRP drains anyway.
I guess that rules out the ready made PEX down tubes that they sell at the big box stores.