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DHW tank questions

Post in 'The Boiler Room - Wood Boilers and Furnaces' started by tuolumne, Feb 22, 2008.

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  1. tuolumne

    tuolumne New Member

    Joined:
    Mar 6, 2007
    Messages:
    172
    Loc:
    Now living in VT, and building new home in VT
    Should I have a check valve on the cold water supply to prevent hot water from migrating out of the tank? How far will it go, with the tee from the supply being 8' above the cold water inlet? If so, what type should I look for? Also, does the DHW tank need its own expansion tank? I will have 80 gallons of water....neither our current home, nor our previous home had one. Our previous home also had an 80 gallon tank. If so, would I tee it off the pressure relief outlet?

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  2. Eric Johnson

    Eric Johnson Mod Emeritus

    Joined:
    Nov 18, 2005
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    Central NYS
    What kind of heat exchanger are you talking about--in indirect with an intank coil or an external hx like a sidearm?

    I have a sidearm and the only check valve I have is the flow check on the boiler water side. Since the hot water from the wood boiler is pumped down through the sidearm, the system flow check naturally keeps it from thermosiphoning back up when the pump stops. If you know how a sidearm works, you'll understand what I'm talking about. If not, ignore what I just said.
  3. solarguy

    solarguy New Member

    Joined:
    Jan 14, 2008
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    Loc:
    southern, nh
    You do not need a check valve on the cold water inlet to your water heater unless you're
    pulling a hot water return off the system to circulate hot water for instant gratification.

    Expansion tanks for hot water heaters are required by code in most places, a small amtrol st-5 would suffice & they cost around 40 bucks. If you put a tempering valve on your heater you really should put one on. This prevents your relief valve from drippling. Be sure the probe on the relief valve is long enough to be in the water jacket of the tank.

    You could also put a heat trap on the hot water outlet of your heater to save energy.
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