Installing a Heat Pump Thermostat
LESLIE: Carl in Arkansas is on the line with a thermostat question. How can we help you?
CARL: I bought an older house and it’s – the thermostat that’s in it now for the heating and air conditioner is an old mercury switch. And what I bought is a Honeywell 5-2 switch, a programmer for 5 weekdays and then 2 weekend days. And what I’m wanting to know is, can I – is that something I can change out myself or is that something I need to hire an electrician to come do? The package says “easy to install” but I’ve looked it over and it doesn’t look like it’s that easy to me.
TOM: Well, look, if you’re uncomfortable with it, I would not hire an electrician. Kind of heat do you have? Is it gas? Oil? What is it?
CARL: It’s electric.
TOM: Oh, it’s electric heat. What kind of furnace do you have?
TOM: Is this a heat pump?
CARL: No, no, no. It’s not a heat pump. That’s one thing I didn’t want was a heat pump.
TOM: It’s a straight electric furnace?
CARL: Right. Straight electric furnace and it has an outside unit, which is also a Trane.
TOM: Uh-oh. Wait a minute. Listen to me. If you’re telling me you have an outside condensing unit that works with this, you’ve got a heat pump. You’ve got the compressor outside and then the furnace inside.
Now, a heat pump is a combination heat pump/electric furnace. That’s the way they’re designed to work. And the reason that that’s important is because the thermostat that you chose – and I don’t know that this is the case or not but it has to be rated for a heat pump.
Because the way heat pumps work is when you set your heat – let’s say you set your heat at 68 degrees. It starts getting cold outside, right? Then inside the house, it falls to 67, the heat pump comes on. Still cold, falls to 66, heat pump stays on. Still cold, falls to 65, now it’s at more than 2-degrees split between what it was set at and what it is. The heat pump says, “I can’t keep up with this. I’m going to bring on my friend, the electric furnace.” So now the electric-furnace coils kick on and then bring the house up to temperature.
But by you not having the right thermostat, what can happen is you can run more of the electric furnace and less of the heat pump, which will significantly increase your electric bill. So, the thermostat you choose has got to be designed for a heat pump.
So I would say your first thing to do is to confirm – I don’t know if you have an HVAC contractor that you work with but get that system serviced. I mean all these compressors have to be serviced once a year. If you haven’t done it, get it serviced, get the refrigerant checked out. While that guy is in the house, have him install a heat pump-rated thermostat. Because you’re obviously uncomfortable with it and we don’t want you to have all those wires apart and just have a problem where you’ve got no heat or no air.
So I wouldn’t do it myself, because you’re uncomfortable with it. And when it doubt, don’t do it. But make sure you use the right thermostat. Otherwise, you may drive up those costs unexpectedly. OK?
CARL: OK. Well, I appreciate it.