Sizing; T&P Indirect DHW Tank

Anthony J. Mangano

Does anyone know what the code requirements are for sizing the T&P relief valve for a DHW Indirect tank are? Is it the total BTU/Hr output of the heating source? Also on the ratings of the T&P, do you go by the AGA Temp. Steam rating BTU/Hr or can you use (the higher) ASME Steam pressure ratings BTU/Hr?

A.J. Mangano

Alan(CaliforniaRadiant)Forbes

Go with

the lowest rating printed by the manufacturer which should be above the boiler input.

Some codes require you to de-rate the relief valve listings, i.e. if the relief valve says 100,000 BTU's max., inspectors may only allow 80% of that. So the maximum boiler size would be 80,000 BTU input.

It depends where the boiler is installed; residence? commercial? school?

It's always best to check with your local jurisdiction.

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Tony Conner

If You've Got...

...an inspection authority saying how to do it, then go with that method. If you've got an inspection authority that will actually GIVE you an answer, rejoice!

The line here for things like steam safety valves, and water side reliefs on steam to water heat exchangers is that "It's left up to the manufacturer or system designer." No guidance, no suggestions, no nothing. No info from ASME or the National Board of Boiler & Pressure Vessel Inspectors either. I find this situation to be absolutely unbelievable.

My pet peeve these days is low pressure steam (safety lifts at 15 PSIG max) or low temp hot water (250*F max) heat exchangers isn't on the radar for the inspection authority. I have suggested to them that in a closed system, or one that could be closed because of isolation valves, if the hot side controls malfunction you could generate HUGE hydraulic pressures on the cold side, along with high enough temps to launch one of these things. They don't care.

Anthony J. Mangano

Thanks

Thanks guys. I spoke to the local inspector who told me the "pressure side" of the T&P is redundant on an indirect water heater, boiler has its own safety.

But a T&P was required for the Temperature safety. He didn't care what size. Huh?

Alan(CaliforniaRadiant)Forbes

That's what I thought

you were talking about....the DHW side.

Yes, the boiler has it's own relief valve, but the DHW side must have a T & P relief valve sized for the boiler; at least around here.

Best wishes,

Alan Forbes

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