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Unpressurized buffer tank in hydronic system-- what do I need to know?

cgregory Member Posts: 6
I'm getting a wood gasification boiler that will operate at a max of 30 lbs. What I want to to is use an unpressurized tank for the required buffer. I assume the boiler does not need to operate at an above-atmospheric pressure, so plumbing will not be a problem. Might I be wrong with this assumption? If so, what do I need to know about making transitions from the pressurized part to the unpressurized?


  • Jamie Hall
    Jamie Hall Member Posts: 23,421
    What part of your system is going to be pressurized? Is this for a hot water heating system?

    There are several ways you could do this, but if this to be a hot water heating system, you have one major consideration: the heating system -- pipes to and from the radiation and the radiation itself -- either has to be piped completely in series from each circulating pump -- which will lead to very uneven heat as the temperature of the water drops off going from radiator to radiator (this arrangement will be very noisy when the pump starts, by the way) -- or it has to be pressurized and held that way.

    If your buffer tank is well above the highest radiation, it could be used to provide the system pressure. You would pump up to it from your boiler, and the return would go back to your boiler. Your circulators could also take water from the tank and circulate through the radiation. But that assumes that the tank bottom is well above -- a story above (8 feet) -- which may not be desirable. The boiler could be anywhere at least a story below the tank.

    However, if the tank is at or below the radiation, that won't work and you will need a heat exchanger in the tank, separating the pressure water system from the atmospheric tank.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • hot_rod
    hot_rod Member Posts: 22,251
    Is it an open lid type of tank? Most use either copper or corrugated stainless tube to install HX coils.

    Tom at Solartechnics shares some good advice and sells components at

    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream