I'm sure this question may have been brought up many times, but I can't seem to get a straight answer. For many years I have been told that setting back a heat pump in a residential situation is not going to save any energy, and perhaps be more energy wasteful. I'll pose the question as simply as possible. I usually heat my home to 69 degrees. I am considering a set back to 64 or 65 degrees for two different periods. In the morning, at 5 AM:, bringing the temp up to 69 degrees. At 7 AM, lowering it until 3 PM... then bringing it back to 69 until 10 PM, then back to 64 or 65 degrees. And at 5 AM resuming the cycle. Is the 4-5 degree setback worth doing? Is the recovery time more costly than what the setback saves? I am of the opinion that the setback really doesn't save anything. I am somewhat aware of the concept of thermal mass, and I think that because of that the heat pump may run more to overcome that situation when bringing the house back up to the higher setting.

Anyone have a difinitive answer?

Setting the temperature back will always save energy. The problem with heat pumps is that they may not be able to bring the house to the temperature that you would like at the time you would like it. This is going to depend on the outside temperature. You must prevent emergency heat from coming on to save energy.

Thermal mass generally rears it's ugly head when during the day the house is absorbing a lot of heat and when the sun goes down, the heat from the mass of the house shows up on the inside where you don't want it.