DHW tank questions

tuolumne Posted By tuolumne, Feb 22, 2008 at 12:52 PM

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  1. tuolumne

    Member 2.

    Mar 6, 2007
    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?
  2. Eric Johnson

    Eric Johnson
    Mod Emeritus 2.

    Nov 18, 2005
    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

    New Member 2.

    Jan 14, 2008
    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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