LESLIE: Carol in Texas, you’ve got The Money Pit. How can we help you today?
CAROL: Hi. Well, I have a heat pump system and to save energy, I’ve been turning it down at night and up in the morning; probably six or eight degrees.
TOM: (overlapping voices) OK. Hmm. How’s that working out for you? Because I bet you’re not saving much energy.
CAROL: Well, that’s what I just found out. Someone had told me something, that I shouldn’t be doing this, and I don’t know why.
TOM: Yeah. I can explain to you why. A heat pump is really a combination of two systems: it’s a heat pump, which is essentially an air conditioner that runs the refrigeration cycle backwards; and an electric furnace, where you just have electric heating coils that come on and the air blows over them. And they work together in the same box.
So here’s what happens. If the temperature in your house is – let’s say you have it set to 70 degrees. If it falls to 69, the heat pump will come on; it will try to bring it the temperature up to 70. If it falls to 68, the heat pump will stay on. If it falls to 67 or more than a two-degree difference between what you would like it to be and what it is in the house, the heat pump communicates to the electric furnace and says, “Whoa. I can’t keep up with this. Bring on the electric furnace and bring me up to temperature,” and then the heat pump will take over again.
So if you turn your heat down at night and spring it back up in the morning – obviously, you’re moving it more than two degrees – you’re essentially forcing the heat pump – excuse me – you’re essentially forcing the electric furnace to come on all the time and that costs about twice or more to run than the heat pump.
So the way to do this is with a special type of setback thermostat which mechanically brings it down very slowly and brings it up very slowly so it protects that two-degree separation and never requires the electric furnace to come on. So if you buy a heat pump, setback thermostat – specially designed for heat pumps – you can have the convenience of turning your heat down at night and up in the morning without triggering the electric furnace. Follow me?
CAROL: Yeah. I see what you’re saying. Is this a special kind of thermostat? Is it something you put in …
TOM: No, it’s a very common thing that you can buy. In areas where a lot of the homes are heated by heat pumps, you’ll even find them in the home centers. But you just want to make sure you buy one that’s rated for a heat pump; not a standard setback thermostat but one that’s set up for a heat pump.
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