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I would like to build a simple wood fired boiler. Burning wood is most efficient if it is burned hot and fast and that can make too much heat. I would like to store the excess heat in an insulated water tank for later use. I would prefer to keep the system as simple as possible. I was wondering if a gravity (what I had always heard called a thermo siphon) system would work for moving the water from the boiler to the tank. The tank could be right next to the boiler. Apart from the question of is this possible, I wonder about how to plumb this. Should the tank be above the boiler? Should the pipes from boiler to tank be the same size? Should the pipes from boiler to tank be inclined up or down? How do you determine the diameter of the pipes? Electricity in my neck of the woods has not always been reliable. With a circulator and a roaring fire if the electricity were to go out it could be a problem.

Thanks for any insight any one can provide.
Mike Kuczek


  • Paul Pollets
    Paul Pollets Member Posts: 3,656
    Gravity won't move the hot water fast enough from the wood boiler to the storage tank. You'll need a circulator pump and aquastat that makes on rise to do so. Also need to consider what happens when the storage tank exceeds 180.
  • STEVEusaPA
    STEVEusaPA Member Posts: 6,505
  • hot_rod
    hot_rod Member Posts: 22,260
    Tank would need to be above the stove, hot water rises.
    If it were an open to atmosphere tank it would boil if over temped

    I think it would depend on ho large the stove HX was, how much energy you tried to move
    If you grab too much heat from the stove they run cold and form creasote

    Ho will you get heat from the tank to the system
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • nibs
    nibs Member Posts: 516
    We have a barrel woodstove, with 1" galvanized pipe running above the fire, heating a 300 gallon hot tub which we use almost daily. It thermosyphons very well. The water in the piping does boil sometimes, but since the tub is open, it is not important.
    Do not want to hijack the thread so if you want more specifics, PM me your email address. I can tell you what we did here, but do not want to outstay my welcome.