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Standby DHW Tank Question

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Cyclist77
Cyclist77 Member Posts: 253
in Domestic Hot Water

SInce installing our indirect dhw tank with the new boiler I have a question. We kept the electric dhw tank and isolated it to be used as a backup. Last night I started wondering about the water in the tank. Should it be drained and refilled every so often?

Thanks!

Comments

  • Jamie Hall
    Jamie Hall Member Posts: 27,188

    Funny how things show up in the middle of the night…

    The answer to your question is n— yes it should. While stagnant water is usually OK, it can decide to grow nasties…

    How often? Well… At the very least weekly, I'd say. And if it's that rarely, I'd run it right up to 140 F and hold it there for an hour every time it is refilled, then turn it off. But I'm sort of conc=servative.

    An alternative would be to pipe it so that the feed to the regular domestic hot water went through it first, but without heating it. That will keep the water in it fresh at all times, and is probably what I would arrange.

    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
    Larry Weingarten
  • hot_rod
    hot_rod Member Posts: 27,256

    You could valve and series the tanks, so fresh water always flows through the electric tank first. If the indirect is down you could valve it off, flick on the electric tank breaker.

    This also give you a small amount of pre-heat the first tank being at ambient room temperature.

    Screenshot 2026-02-22 at 9.38.07 AM.png
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
    plumbworkerLarry Weingarten

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