Can the water heater tank get overfilled with a D'mand system?

The Tank Can the water heater tank get overfilled with a D'mand system?

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  • #13051
    JK
    Participant

    Everybody,

    The building I’m working at is considering using the metlund D’mand system but reading their literature on how it works, it says it is taking cooled down water in the hot water piping and pumping it into the cold water line. My question is if the cold water line is all filled, where would the excess water end up? I wouldn’t want to overpressurize some piping and overstrain the pump, but then when I thought about it, it may go back into the water heater tank. So my question is when a water heater tank is filled, is it filled up to the top? Can you overfill a water heater tank with this system until someone activates the faucet? I have 20 feet of 1-1/2″ and 40 feet of 1″ hot water piping main to the bathroom which I calculated to be about around 3 gallons of water having to be pumped back to the tank. Thanks for any help.

    JK

    #13052
    Randy Schuyler
    Keymaster

    Any system that is under pressure is full all the time: the heater, the piping. If there is no backflow preventer or pressure reducer, then the water would back up into the city main. If there is, then you probably need an expansion tank anyway, and the water would back up there. With those devices and without an expansion tank, you probably will experience destructive thermal expansion. Or rather, your water heater and piping will experience it.

    Randy Schuyler

    #13058
    Larry Weingarten
    Participant

    Hello: Think of this as a loop. The D’mand pump simply moves water around the loop. When the pump runs, it pushes water from the hot line into the cold. That makes its way into the heater, replacing water drawn down the hot line to the pump. One big loop 😉

    Yours, Larry

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