TPR Discharge Pipe Piped Correctly?

Hey guys, I got a Polyethylene TPR discharge pipe that is piped into was waster receptor with a P-trap. Just wanted to confirm that this is a proper installation?

It’s PEX, not straight poly, usually black in color. It needs to have an air gap, not an air break. Also that dedicated ptrap will dry out and allow sewer gases into the house (assuming it connects to the house drain).


Not proper!

It should discharge into a NON-TRAPPED drain with an air gap. Plus the termination should be visible as to be able to see and detect leaks from a faulty valve.


Thanks for the help and the correction on the tubing. This water heater was not easy to get to. I thought the markings on the tubing read PE, but I must have been mistaken. I had to strain to even get a glimpse of the markings.

It does connect to the house drain.

Not to nitpick but yes the TPRV discharge pipe should go into a standpipe via airgap not airbrake. There may also be regulations for the height of a standpipe as well. Best to just call it out as being incorrect and have a plumber look at it.


I think you find this on tractor-trailer, not plumbing :smiley:

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Air break not airbrake.

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Correct… … …

Hey Harry -
The p-trap is a no no.
Plus the p-trap would be useless even it wasn’t a no no.
You probably already know this, but if not…

Ref IPC504.6 Requirements for discharge piping.

The discharge piping serving a pressure relief valve, temperature relief valve or combination thereof shall:
1.Not be directly connected to the drainage system.
2.Discharge through an air gap located in the same room as the water heater.
3.Not be smaller than the diameter of the outlet of the valve served and shall discharge full size to the air gap.
4.Serve a single relief device and shall not connect to piping serving any other relief device or equipment.
5.Discharge to the floor, to the pan serving the water heater or storage tank, to a waste receptor or to the outdoors.
6.Discharge in a manner that does not cause personal injury or structural damage.
7.Discharge to a termination point that is readily observable by the building occupants.
8.Not be trapped.
9.Be installed so as to flow by gravity.
10.Terminate not more than 6 inches (152 mm) above and not less than two times the discharge pipe diameter above the floor or flood level rim of the waste receptor.
11.Not have a threaded connection at the end of such piping.
12.Not have valves or tee fittings.
13.Be constructed of those materials listed in Section 605.4 or materials tested, rated and approved for such use in accordance with ASME A112.4.1.

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Thanks for the help. I have a crazy time with these TPRV discharges. Almost every home has issues in my area. Even new installs. This probably the most common method in attics. It’s starting to get annoying lol.

It’s part of the DWV drainage system. Same as dumping into a floor drain with an air gap. The p trap is a requirement and it’s fine. Try to remember those requirements you listed are for the discharge piping. Once the discharge piping enters the DWV system it’s game on…it’s going into a drain pipe.

I just did a house today with improper TPRV discharge pipe size, no seismic straps and no expansion tank. Call out the use of that PEX fitting on your TPRV discharge piping. It needs to be increased to 1” and supported at the end of the pipe. Of course this is only if it was installed after 2018 :slightly_smiling_face:.

Hey Martin - I’m down with the theory.
But - indulge me here.
I always let sensibility take the pole position on anything that looks unusual.
First - the reason I mentioned that the p-trap (as visible) would be useless is because - how’s it suppose to trap anything? Is the homeowner going to keep filling it with water?
But anywhos - What I’m seeing in Harry’s photo is a PEX? discharge “tube” jammed into a p-trap. And if that ain’t considered a discharge trap, then I don’t know what is. Nor can I figure out where the readily observable discharge point would be. Or a visible air-gap.
I may be over visualizing - but I’m guessing that if the TPRV pops, steam is coming full blast and straight up out of that receiver pipe.
Its just me, but I would insert that photo in the report, with the comment “this was almost a good idea” :flushed:
Maybe I’m seeing it wrong?
Maybe it could be improved with an indirect drain attachment?

Probably and that’s OK floor drains dry up all the time. They make special mineral-based solutions to slow the evaporation process.

The discharge tubing ends at the end of the 3/4” tubing. Once it enters a drain it enters the sanitary system and has a different set of rules, it’s no longer a potable water pipe. The proper way would probably be to put a 3”x2” increaser on the end of that stand pipe and the discharge pipe from the TPRV would drain into that increaser with an air gap.

Hope that helps. TPRV discharges pipe gets brought up on this forum all the time.

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If we know anything, we know homeowners can certainly be creative.
Check out this photo of a recent inspection. The house was a flip, and on a slab. The flippers relocated the WH to an interior closet. SEE PHOTO.
TPR discharge configured with flex water tube just laying in a plastic bucket. Plastic flex hose connected to a sump pump. The plastic hose went up thru the ceiling - thru the attic - terminated thru the soffit (12 feet in the air). Good times.
TPR discharge to bucket

Confused here Martin. So you are saying a p-trap is fine in a TPR blow-off? Just want to check my Ps and Qs on this…

My goodness, you’re picky!

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It can’t be part of the discharge tubing that is connected directly to the TPRV. In other words you can’t make that a straight piece of tubing into a trap using fittings or any other method.

The TPRV discharge tubing can drain into a P-trap if it is connected to the building drainage system. The reason for the P-trap is to have a water seal to prevent sewer gas from entering the residence.

That’s awesome. I wonder if that TPRV was seeping water? Was there an expansion tank or a thermal expansion valve on the water heater?