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Maximum SAFE temperature for domestic hot water tank

The problem with having hot water heated by a wood burner is that a GOOD fire raises the hot water temperature pretty quickly. In cold weather, I'd like to have a good fire all night (radiators don't do too much) but my OH says that over 65 degrees is 'dangerous' (fo the tank - rather than us. I have NO idea why he thinks this except that we have a 'dump' radiator to take water over that temperature which is currently disconnected (because he's rewiring everything in bits and pieces while putting in a new control unit.) What WOULD be a dangerous temperature from the tanks point of view.


  • hot_rodhot_rod Posts: 11,629Member
    65C, 149°F I think you mean? A pressurized tank? Depending on the tank material type, of course. I know glass lined steel tanks are not as happy above 180F. Certainly plastic and composites have a limit.

    Really any tank that sees a wide and high temperature change undergoes more stress.

    Most important its you have a working, listed mixing valve to limit water temperature to the building 120F, 49Cs the most common temperature limit.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    The magic is in hydronics, and hydronics is in me
  • Jamie HallJamie Hall Posts: 10,548Member
    And a pressure/temperature relief valve...

    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England.

    Hoffman Equipped System (all original except boiler), Weil-Mclain 580, 2.75 gph Carlin, Vapourstat 0.5 -- 6.0 ounces per square inch
  • GroundUpGroundUp Posts: 545Member
    There are an awful lot of regular cheapo WH tanks from the big box that have been running 170F+ DHW temps for many years with no issue. Depends on what you have
  • JanetGeorgeJanetGeorge Posts: 2Member
    Thanks hot rod. Yes, did mean 65C. It's a copper tank - but the rest of it is beyond me.
  • hot_rodhot_rod Posts: 11,629Member
    Is it a sealed pressurized tank?
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    The magic is in hydronics, and hydronics is in me
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