Hello. I have a dual zone baseboard system for heating. The cooling is run separately from upstairs switch. I wanted to replace the old thermostat downstairs with a programmable thermostat. When I popped off the thermostat it only had two connections. This thermostat only runs downstairs heat. An electrician friend said the programmable will work with the two writes but the home depot employee said you need three. Anyone have any knowledge on the subject?

I greatly appreciate your help in advance