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relief valve btu or psi

sebast Member Posts: 30
I ran accross today an old bryant boiler that had a new relief valve installed last year and was leaking. With this perticular boiler the input btu`s was 650,000 and the relief valve was rated 30psi and btu rated for 675,000. I know all the reasons and solutions why it could be leaking, but today made me think about the btu`s. ( boilers operating pressure was 12 psi )What does the valve care what is the input rating of how fast the water will heat as long as it maintains operating pressure. I have always just replaced the relief valves to their proper size and never gave it the thought why ? please reply.


  • It matters a lot

    Relief valves are designed to be able to dump enough water to prevent the boiler from building excess pressure.

    If too small a relief valves is installed and the boiler should malfunction, there's a good chance the boiler could overwhelm the relief valve output causing property damage and physical harm.

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  • Mike T., Swampeast MO
    Mike T., Swampeast MO Member Posts: 6,928

    Like so many thing we take for granted the remarkable engineering behind a safety valve that opens for both temperature (BTUs) and pressure.

    Remember that there ARE grades of such--the cheapies are typically used on tank hot water heaters and the good ones one boilers and similar.

    If a good-quality T&P is showing leakage after such a short period suspect that BTUs in are regularly and greatly exceeding BTUs out.
  • seabee570
    seabee570 Member Posts: 89
    relief valves

    on large power boilers the relief valve must be matched to burner input...and not allow the pressure to rise above 6 percent of input. this keeps the boiler from coming apart ...the whole purpose of the valve is to be able to relieve the pressure in the boiler according to the btu input of the burner...the relief valve does care what the input of the burner is because that is how it keeps the boiler from exploding...thus the btu input of burner must be used to determine what the relief valve rating is...by your statement,I would be careful working on or around boilers
  • hr
    hr Member Posts: 6,106
    Relief and T&P valves

    are two different animals.

    Generally boilers have pressure relief only valves. And yes they need to be sized to the max pressure and BTU load. It is not at all expensive to step up in BTU range, generally. Most larger BTU rated valves have 1" or larger discharge to handle a relief of that size.

    I prefer B&G brand for relief. Much better built than some of the "standard equipment" brands boilers are shipped with. Not uncommon to see the cheapies weep at 20 psi!

    T&P valves have a probe in addition to the pressure relief. These are seen in water heaters where an over temperature protection is needed. Usually seen in 125 or 150 PSI and 212 degree settings.

    Don't ever use a DHW T&P relief valve on a boiler. I've seen it many times! The pressure relief is far in excess of what most boilers are designed to handle. Generally boilers are tested to 45 psi and relief valved at 30 psi.

    Installing a 150 psi valve in a boiler is "rocket science" as that's what you may see!

    hot rod

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