TPV discharge pipe

[Lawrence Thomas]

Hey guys,

I am just not sure about this water heater discharge pipe. Its PEX, but it has a pressure/temperature rating label of 100 PSI at 180 F. Is this OK for a TPV discharge? (I turned the picture sideways for ease of reading the label).

[Jerry Peck]

Yes, PEX is permitted to be used for the discharge pipe from a T&P relief valve.

That 180F rating is at 100 PSI, a T&P relief valve may have, at most, 15 PSI (I found that 15 PSI number in some research I read about PEX being used for T&P discharge piping).

Remember, the end of the PEX not connected to the T&P relief valve is open, no pressure build-up.

Also remember that when the T&P relief valve opens, cold water flows into the water heater, the longer the T&P is open, the cooler the water in the tank gets, the cooler the water in the tank, the cooler the water going out the T&P valve and its discharge piping.

PEX does, however, need to be secured (don't want it whipping around, do we?).

CPVC has the same 100 PSI/180F rating, and also needs to be secured.

[Lawrence Thomas]

Thanks for the quick reply. I am just finishing up yesterday's inspection report.

[Jerry Peck]

I should also have included this for CPVC - those all plastic threaded male adapters used to connect the CPVC to the relief valve outlet ... NOT ALLOWED.

The all plastic threaded male adapters are not approved for use in hot water system fittings.

The plastic threaded male adapters at the relief valve and other locations in the hoot water system are supposed to be the ones with the brass threaded part ... NOT all plastic with plastic threaded part.