Controlling separate heat and AC units from a single thermostat

Question

I currently have central air in the attic and furnace in the basement for the heat (steam radiator heat). I have both wires run to the same location but have two thermostats. Can I wire them both to one thermostat? I have a picture of the thermostat that is currently used for the AC only. Any help or suggestions would be helpful.

Answer 1

Yes.

1. Remove the jumper between the R and Rc terminals.
2. Connect the R wire from the heating system to the R terminal.
3. Connect the R wire from the cooling system to the Rc terminal.

Then you should be able to follow the thermostats installation guide, to connect the rest of the wires for the heating and cooling systems.

Unfortunately, without seeing the wiring in the heating and cooling systems, it's impossible to tell you how to connect the rest of the wires. Typically W is for heat call, Y is for cool call, and G is for fan. However, there's no standards or requirements that make this universal.

It appears that you're using a Honeywell Wire Saver device, which is why the cooling system uses the K terminal instead of Y. I'd leave that wired the way it is, and simply add the heating call wire (from the heating system) to the W terminal.