How to add a Smart Thermostat to a Millivolt Ignition Gas Heater

[@earldavison3513]

Nice build and adaptation for your off grid cabin.

[@samuelwiltzius]

Thanks! I’m so excited this works.

[@davidherrera6885]

Do you only need one relay if you're not powering the fan?

[@samuelwiltzius]

Correct. The relay simply creates an ON state, allowing the millivolt system to signal on/off as requested by the thermostat. The fan is a separate feature.

[@Gunzw1-q3e]

So what are you using to power your 12v to 24v step up converter? Also, what gauge of wire are you using?

[@samuelwiltzius]

I have a 14kwh LiFePO battery that powers the cabin via an inverter. There is a separate fuse panel for low voltage appliances in the cabin that bypasses the inverter. The whole panel is on a 10 amp fuse. Don’t remember exact wire size but I followed a readily available reference chart. I think 14 gauge stranded.

[@Gunzw1-q3e]

Thank you!​@@samuelwiltzius

[@MM-cg8cg]

I get it. So: the millivolt or no millivolt, the thermometer is still basically turning the heat and fan on and off based on its mercury thermosensor, so you just hook up the input and output of the millivolt thermometer to relays and control the relays in smart thermometer. Okay.

[@Jedidiahs]

Wow. You know your stuff.