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Wood Boiler set up...

kcopp Member Posts: 4,440
I have a customer who has a existing low pressure outdoor wood boiler. They are selling and need to have a more reliable heating system (for the financing) that will work if they leave for days/ hours.
I can get my head around the piping for a secondary boiler but am having a hard time figuring out how the system will be wired.
Where and what sensors do I use and how do I wire it so that the wood boiler and LP gas boiler are on/ off when they are supposed to be or not be on?


  • Ironman
    Ironman Member Posts: 7,379
    Use an ETC that senses when the SWT from the wood boiler gets to 160* or above. Wire the house t'stat through its "NO" contact to turn on the circ or ZV that would allow the ODWB to heat the house. Wire the gas boiler through the "NC" contact. Sometimes a relay is needed, but you get the picture.

    The ETC is simply choosing either the ODWB or the gas boiler depending upon the SWT in the ODWB.

    Arrange your piping and circulators so that it's an "either or" situation so that the gas boiler won't back heat the ODWB.

    Oviously, a heat exchanger is needed.
    Bob Boan
    You can choose to do what you want, but you cannot choose the consequences.
  • hot_rod
    hot_rod Member Posts: 22,254
    the system on page 38 may be close to what you are trying to do. Think of the boiler and tank as one complete unit.

    If the OWF have a large water volume, a ∆T (solar controller) control is another nice control option. And outdoor reset is a great control also, to maximize either unit. Wiring schematic on page 39

    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • Solid_Fuel_Man
    Solid_Fuel_Man Member Posts: 2,646
    Keep in mind that either glycol will be needed, or you are forced to waste heat and keep the OWB heated to some degree. Not a fan of outdoor boilers.
    Serving Northern Maine HVAC & Controls. I burn wood, it smells good!