I have a 2-stage heating system that switches from an electric heat pump to a gas furnace when the outside temperature drops to 10 degrees or when the temperature differential (set/actual) is more than a few degrees. My question is this: is it worth it to program the thermostat to a lower setting during the day if the system has to switch to gas to bring the house back to a comfortable temperature for the evening? Isn't a programmable thermostat doing more harm than good in this case (for my wallet and for the environment) by forcing the backup expensive gas backup system to come on?
biozen 1-5-7 1:43pm
Good question. You would be correct, IF you were using a normal, run-of-the-mill, clock set back thermostat. Bouncing the temperature up and down would cause your gas backup furnace to come on to keep up with the demand for heat. Read my post here  about how heat pumps work.
The solution is to purchase a clock thermostat that is specifically designed for a heat pump. The difference is that a heat pump set back thermostat moves the heat up and down SLOWLY, so as to not exceed the few degrees differential setting that cues the backup gas system to come on. These are a little difficult to find sometimes, but if you check with a local professional HVAC supply company, order online  or check with the heat pump manufacturer, I'm certain that one can be secured.
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