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merging two thermostats into one

dpinn91
dpinn91 Member Posts: 2
edited May 2020 in THE MAIN WALL
i have an outdoor wood burning boiler system that pumps hot water to my furnace(but none of the thermostats i'm talking about deal with this). inside my house i have two thermostats, one only runs the blower motor and is used when i am burning wood as the water in the system is already hot. the other runs the blower and pumps propane to heat the water when i am not burning wood. i bought a two stage thermostat with adjustable offset to be able to automatically switch back and forth in case the fire dies but cant seem to figure out how to wire everything together... do i just leave the stage 1 heat spot empty and when it calls at stage one it will just run the blower or do i need to do something else.

Thanks

Comments

  • Ironman
    Ironman Member Posts: 7,367
    You need extra controls, a piping strategy that isolates the hydronic coil from the furnace when gas is used, etc.
    Bob Boan
    You can choose to do what you want, but you cannot choose the consequences.
  • dpinn91
    dpinn91 Member Posts: 2
    do i already have this since i dont think im changing anything... both of my inside thermostats are already hooked into the furnace doing the same functions i want, i am just trying to eliminate an extra tstat (plus my new one is wifi enabled to allow for more control)
  • HVACNUT
    HVACNUT Member Posts: 5,804
    edited May 2020
    I'm not familiar with wood boilers so I don't know if this is feasible, or safe. I'd assume the boiler has its own safety circuit.

    Just a single stage heat/cool thermostat.
    Use the "Fan On" feature for when wood burning is used. The thermostat temperature is set so all you is need fan. Use a 24v isolation relay powered by G on the thermostat. N.O. contacts to cycle the fan through a B, "close on temp rise" limit.

    When the fan is set to "Auto" fan operation will be energized through W on the thermostat as part of the normal heat cycle.

    Is this a dual fuel boiler?
    Is there a furnace?
    I know there's a hydro coil.

    Wood burning by WiFi. Is that a thing?

    Not exactly auyomatic staging though is it?
  • Ironman
    Ironman Member Posts: 7,367
    I've done wood boiler installations for years and seen all kinds of foolishness done by DIYs as well those who were supposed to be pro's.

    When I started in this trade 45+ years ago, I worked in large commercial HVAC and controls, so that comes more naturally for me than some. When I began doing ODWB installs over 15 years ago, I saw the two thermostat approach and couldn't believe that the ODWB purveyors thought that was a viable means of controlling it. That approach will cause one thermostat to back feed through the other one and bring the a/c compressor on when the other one energizes. It will also cause the gas furnace to back heat the ODWB.

    I have a fairly simply method that uses the same standard t'stat that the primary system came with plus some addition controls. It does require either a motorized 3 way valve or p/s piping at the indoor coil.

    I have yet to find any thermostat that will accomplish everything necessary; it requires the additional components that I use.
    Bob Boan
    You can choose to do what you want, but you cannot choose the consequences.
    HVACNUT