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Convert nest to support millivolt



  • adambuild
    adambuild Member Posts: 409
    Would the TACO SR501 do the trick as well?
  • andrewco
    andrewco Member Posts: 104
    Adam - yes, that would work as well.

    It looks like there are multiple versions of the SR501. I'm thinking you would want to go with the SR501-EXP so you have the mv contacts to control the device. I don't see that on plain SR501.

    Quick search shows the pricing on the TACO units are more....unless you happen to have one lying around :-)

  • tdibratt
    tdibratt Member Posts: 0
    I have a 24V transformer on my Furnace. It provides power to my Nest thermostat to control furnace. I also want to control my Propone Millivolt fireplace with a second Nest thermostat. So the thought was I would bridge the 24V to the second Nest. But since the millivolt system is not expecting a 24V power connect, I was thinking I would connect the mllivolt lines to a SSR and the Nest to the input side of the SSR. Something like this one.

  • Jamie Hall
    Jamie Hall Member Posts: 19,452
    Not sure about the compatibility of the solid state device with millivolt. Might work. More likely might not. You'll probably do better with a standard 24 volt coil relay and contacts rated for millivolt switching.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • Zman
    Zman Member Posts: 7,375
    Some high voltage contactors won't pull in tight enough for millivolt circuits. Either the taco in the original post or Jamie's suggestion will work better.
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
  • andrewco
    andrewco Member Posts: 104
    Also - using the same 24v circuit to power whatever you are using to control the millivolt circuit for the propane fireplace as you are using for your furnace doesn't seem like a good idea. If you have a separate secondary off the transformer, then yes but wouldn't use the same one.
  • Motorapido
    Motorapido Member Posts: 292
    I just finished a project in which I wanted to control the millivolt gas heater at my vacation house (deep in woods, so millivolt is necessary to keep the heat on when the power goes out, which it does around here with some regularity. I used an Emerson fan control center -- a combination 24v transformer and relay. The 24v transformer powers the wifi Honeywell T5 thermostat. When the wifi thermostat calls for heat, the relay closes, and I have the relay terminals wired in parallel with the existing millivolt thermostat connected to the gas heater. I keep the millivolt thermostat set to 55 degrees. This is my safety thermostat. If power goes out, the wifi T5 Honewell thermostat and the Emerson fan control center have no power an are taken out of the equation, and the millivolt thermostat keeps doing its work to keep the property at 55 degrees. Here is a link to the Emerson fan control center that I used https://www.amazon.com/gp/product/B002CJHLWC/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1

    Here is a link to my thread in which Mattmia2 tells me which thermostat wires to connect to which terminals on the fan control center. https://forum.heatinghelp.com/discussion/183623/how-to-wire-stat-to-trigger-mechanical-relay

    My system is working wonderfully. Not sure why the c-wire-required thermostat manufacturers do not provide instructions for using smart/wifi thermostats with millivolt gas valves since it turns out to be simple an inexpensive to do. For those with properties that must heat during electricity outages, millivolt rules and there are plenty of millivolt gas valves out there in gas fireplaces and gas stove heaters and wall-mount gas hot air furnaces.