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lowering fluid temperature from the wood boiler

LesliePercy Member Posts: 3
With a wood-fired boiler, the temperature of the water to the load will be high -- first, because it is necessary to prevent condensation in the boiler, so the temperature will be at least 140 degrees; and second, because it is not easy to control the burning so that the temperature may rise beyond this to near the boiling point. Thus the temperature of the outgoing water may be very much higher than the 120-130 degrees wanted for a low-temperature heating system. The method usually given to achieve this reduction is a mixing valve which combines the lower temperature water from the return to the overheated supply; however it does not seem to me that this would be enough. I suppose that one possibility is to install a large buffer tank before the mixing valve, but, unfortunately, we don't have room for such a tank. The problem may be particularly bad with plastic pipes. Any suggestions?


  • Ironman
    Ironman Member Posts: 7,399
    Why do you think the mixing valve is not sufficient?
    Bob Boan
    You can choose to do what you want, but you cannot choose the consequences.
  • hot_rod
    hot_rod Member Posts: 22,483
    Is it a multi zoned system? Is the boiler sized to design load?

    It is a challenge to control wood fired appliances to ever-changing heat loads. Most wood burners learn the value of a buffer tank early into their first year of burning :)

    You want a return protection device, like a thermostatic mix valve, or pump/valve assembly. With a good protection you could crank down the boiler operating temperature.

    A dump zone might be a good option also if you worry about more fire than load.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • Solid_Fuel_Man
    Solid_Fuel_Man Member Posts: 2,646
    Mixing valves are used extensively for what you want to do. Not a unique situation, hot rod's suggestions are good.
    Serving Northern Maine HVAC & Controls. I burn wood, it smells good!