Detecting when a regular thermostat is ON or OFF

I think I?m looking for something very simple but not being an electrician, I?m hoping someone can point me in the right direction as far as what zwave device to look for/purchase.

Basically we have a simple thermostat for an electric fireplace (I joined a picture)
The thermostat is not really used as one to automatically start the fireplace depending on the temperature… but rather it is used as a simple on/off switch… ie.: it is either always manually turned all the way ON (for a couple of hours, until the occupants are comfortable with the temperature in the room) or manually turned all the way OFF (to ensure the fireplace will not start by itself when nobody is in the room, wasting heat)

I?m not necessarily looking to replace his thermostat, but rather I was hoping to hide a zwave module behind it (inside the wall) that would at least detect when the thermostat it ON (so that I can then start his ceiling fan)

Any idea/suggestion? (I included picture of the thermostat… I noticed it says 5W on it, not sure if it makes a difference in my options or not)

Of course I assume I could change the whole thermostat for a zwave model but it seems to me a little overkill.,. (and probably more expensive?)

Thanks for your help