I am changing the old analog thermostats around my home with new "smart" thermostats. More specifically, I am installing some Sinope TH1124ZB thermostats. Everything was going swimmingly until I popped open my bathroom thermostat to find the 2 wire thermostat connected to 3 wires in the wall. I don't know the proper terms, but the thermostat red wire was connected to 2 black wires from the wall, and the black thermostat wire was connected to another black wire coming from the wall.
I assumed that the extra 3rd wire controlled the fan for the heater in the bathroom. When I turned up knob in the old thermostat, a fan would turn on. I think I have a fan forced convecting baseboard heater in the bathroom.
Is it safe to replicate this connection with my new thermostat? The very sparse installation guide only shows how to replace existing 2 wire thermostats connecting to 2 wires, and I can't find the right search terms to google to find an example with 2-wire single pole thermostats connecting to 3 wires.