LESLIE: Kim in Missouri is having some issues with a heat pump. To quote her directly: "It wigs out at 32 degrees or below."
Welcome, Kim. What’s going on?
KIM: Yes, I’ve just noticed that my heat pump, when it hits around freezing or below – and that it just doesn’t keep up anymore. It just …
TOM: Now, so does it get cold in the house when that happens?
KIM: Yes, yes.
TOM: OK. So let’s just talk a bit about the way heat pumps work, because there is a secondary system built into it that may not be functioning properly. Heat pumps have an electric-resistance furnace built into them, as well. And what happens with a heat pump is if you set your thermostat at, I don’t know, say, 72 and it falls to 71 or 70, the heat pump stays on and tries to maintain it to get it back up to 72. When it gets to 69 or below, the heat pump says, "Whoa, I can’t keep up with this so I’m going to bring on my electric, backup resistance heat to bring it back up to within that 2-degree differential."
Now, if there’s something wrong with the resistance-heat component of your heat pump, that could be why it’s not keeping up, especially in super-cold temperatures. So, that is most likely the source of this issue.
KIM: OK. OK. But …
TOM: And it’s a call to a service man to make sure because – do you have, on your thermostat itself, a setting that says "emergency heat"?
KIM: Yes, I do. Mm-hmm.
TOM: Now, have you ever put it on there and had it work fine?
KIM: Yes, when I switch it over to there – to that – this red light comes on and the heat comes out warm.
TOM: Yep. That’s right. Because that is turning on, without the switchover happening, the electric furnace. I suspect there’s a problem with your control circuit and it’s not balancing between the two.
KIM: Oh, OK.
TOM: When you manually turn it on, you’re actually turning the heat pump off and the electric furnace on; that’s what the emergency heat setting is.
KIM: Oh, OK.
TOM: So we know we have coils that work, we know we have a heat pump that works; they just don’t work together.
TOM: So I think that’s probably the heart of the situation.
KIM: OK, OK. So I just need to have somebody come and look at that then and fix it.
TOM: Yep. Alright, Kim?
KIM: Alright. Thank you.
TOM: Alright. Yeah. Good luck, yeah, because you don’t want to run that electric furnace a lot, because it costs about two or three times as much to run that as it does to run the heat pump.
KIM: OK. That makes sense. Thank you.
TOM: You’re welcome, Kim. Thanks so much for calling us at 888-MONEY-PIT.