Have a propane gas fireplace, controlled by a hand held remote control thermostat. Wish to install a wall mounted wifi controlled thermostat, heat only. Seems that all available thermostats operate with a 24V system and I have been told that my fireplace requires a milivolt system. How do I resolve this problem. It is a country home which I only visit occasionally during the winter.
Can a wifi thermostat to control milivolt operated fireplace
fireplacethermostat
Related Solutions
The YELLOW or Y terminal at the furncae/ air handler is a dummy terminal for convenience, it is not required to be used, you could send Yellow directly to the AC unit out doors. Common will be used since the Common leg of power comes from the transformer which is in the furnace. The Yellow going to common likely if you trace it back it in fact is Common leg of the 24 v power supply.
You'll need a transformer to step down mains voltage, to 24 volts that the thermostat can use. And you'll need a relay that can work with 24 volts.
You'll wire it up something like this.
When the thermostat calls for heat, the relay contact will be pulled closed. This will signal the fireplace to turn on.
NOTE: the three contacts used on the thermostat are R, W, and C. In the drawing the C may or may not look like a C, so I just wanted to make that clear.
Related Topic
- Ecobee 4 installation – No C constant 24V option on Furnace
- Wiring – re-wiring/retro-wiring a Carrier 40MVC024 ductless A/C for external thermostat: guidance
- Honeywell WiFi thermostat install
- Honeywell T6 PRO Z-Wave Thermostat (model th6320zw2003) exhibits very erratic behavior after battery replacement
- How to convert the fireplace switch into a thermostat switch
Best Answer
No problem.
First, the furnace must be designed to have an external millivolt thermostat. A millivolt thermostat is a very simple creature, it has 2 wires going to it, and it shunts those to call for heat.
Second, the smart 'stat will need a 24V power supply. This is available from any $15 thermostat transformer, such as many designed to mount in junction box knockouts or on the cover of a junction box. The 24V wires go to R and C on the smart 'stat. It goes without saying, this smart stat will not work with the power out.
The smart 'stat cannot directly talk to the millivolt furnace. However since a millivolt 'stat simply shunts the two wires, a relay can be used to shunt those same two wires. The NO contacts of the relay go to those two wires. The coil winding of the relay goes to W and C on the smart 'stat.
And that's it.
Now one more thing. A wonderful feature of most millivolt furnaces is that they are able to run normally when the AC power is knocked out. It's the difference between shelter in place, or needing a hotel room. ** Now, the smart stat will lose its 24VAC when the AC power fails, so it will not be able to command the relay to turn on. For that reason, leave an analog millivolt stat in parallel with the relay. Set it to 40F so it stays out of the way, then when you need it, you can set it to your desired temp and it will shunt the wires and make the furnace kick.
** Difference between your pipes freezing or not. (As if anyone would install a millivolt furnace in the snowbelt, ha ha, they are all used in Florida and California of course. You can't even buy them in the snowbelt, nobody carries them and your HVAC guy doesn't know what they are).