Reply To: T&P relief valve discharge line pressures

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Jerry Peck


For information.

I do Private Building Inspections and see the following freqently.

Water heater T&P relief valve, 3/4″ opening, 3/4″ discharge line has 5-7 elbows, length is 20′-30′ (some even longer), goes down under slab, across under garage, up and out the side wall.

I know Watts limits the number of elbows to 4 maximum and the total length to 30′ maximum, and it must drain downhill and not be trapped.

Obviously, what I see does not fit those requirements.

The local Chief Plumbing Inspectors (nor the Plumbing Inspectors under them) do not enforce the ‘no trap’ or maximum number of elbows. This holds true in Miami-Dade County, Broward County, and Palm Beach Count (where I inspect).

Their reaoning is that the T&P discharge line only need to “drain dry away from the valve so the valve does not corrode closed, the pressure from the valve will blow the line clear after it releases”, the line doesn’t need to drain dry its entire length. I have been unsuccessful in changing their minds.

SylvanMP would not like what I see (I don’t either).

I thought I would start with my question, and depending on the answers, go forward to the typical installation I stated above.

I know SlyvanMP will not have anything good to say about having 20′ trapped and full of water all the time.

All information is appreciated.

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