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Maximum SAFE temperature for domestic hot water tank

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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.

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  • hot_rod
    hot_rod Member Posts: 22,258
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    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
    Living the hydronic dream
    Canucker
  • Jamie Hall
    Jamie Hall Member Posts: 23,438
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    And a pressure/temperature relief valve...
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
    Canucker
  • GroundUp
    GroundUp Member Posts: 1,926
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    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
  • JanetGeorge
    JanetGeorge Member Posts: 2
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    Thanks hot rod. Yes, did mean 65C. It's a copper tank - but the rest of it is beyond me.
  • hot_rod
    hot_rod Member Posts: 22,258
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    Is it a sealed pressurized tank?
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream