# convert from wall switch control to wall switch + thermostat?



## canadavenyc (Apr 23, 2020)

The previous homeowner of our house installed a gas fireplace that is turned on or off from what looks like a light switch on the wall, with an accompanying rotary fan control switch next to it in a double-gang arrangement. I'd like to add a thermostat, if possible, so that when I flip the wall switch ON, it will turn on the thermostat, which will turn the fireplace on and off as needed to maintain a particular room temperature; then when I flip the wall switch OFF, it will cut power and disable the thermostat.

The fireplace is a Kingsman Fireplaces unit, model number MDV31. Page 33 of the manual mentions that a thermostat can be hooked up, or a wall switch: https://kingsmanind.com/wp-content/uploads/31-Man17.pdf. The brochure, under "Thermostat:", says this: "Wall Mount Millivolt or Programmable Thermostat".

So just so I'm clear--how would I hook up a wall switch in series with the thermostat? It's been a while since I took the switch cover off to look at the wiring, but if I recall correctly, it's just a red and white wire going to the existing wall switch. So I take it those would connect to the thermostat instead? If so, then how does the switch get wired to that?


----------



## begreen (Apr 23, 2020)

The milivolt thermostat circuit is 100% independent of the 120V line voltage circuit. Don't combine the two! Just install a low voltage thermostat around the corner or somewhere in the room that is not facing the fireplace. The thermostat itself contains a low-voltage switch. If the thermostat is calling for heat and the fireplace is switched off then nothing happens until the fireplace is switched on by the current wall switch.


----------



## canadavenyc (Apr 23, 2020)

Hi, thanks very much for your reply. Sorry--I may have been unclear--there isn't any 120V line voltage happening. The "light switch" is just a switch that LOOKS like a light switch, but is apparently just a switch to turn the gas fireplace on/off--not hooked a 120V circuit.

The switch is in a good place to install a thermostat, so preferable (if possible) would be to install a thermostat right next to the wall switch.

So if I understand what you're saying: rather than wire the switch to the thermostat and then wire the thermostat to the fireplace, you're saying I should wire the fireplace *separately* to the thermostat and the switch, so that the switch and thermostat are not connected to each other but are both connected to the fireplace; correct?

If so, I'm not sure that would work--the manual says "Only one on/off device (manual on/off, remote control, or hard wired thermostat) should be connected to the appliance at any one time, this is most important when installing an insert or stove as the on/off rocker switch is installed at the factory."  That sounds that would prevent your solution from working, wouldn't it?

Not sure if it helps any, but here's what the manual shows for hooking up a thermostat:


----------



## begreen (Apr 23, 2020)

Low voltage wiring is not supposed to be in the same box as high voltage. What I suspect is in the double gang box, if wired correctly, is the blower rheostat and a power switch that switches a receptacle into which the blower plugs in. This is illustrated on page 24 of the manual. The low-voltage thermostat circuit should be completely independent.


----------

