I have a heat pump. Last night the temperature dropped to 20 degrees outside. The heat pump usually works pretty well. I put a thermometer on the vent just to check the output temperature, since it didn’t seem like the air was hot. The temperature was reading about 78 degrees coming out of the vent. I turned up the thermostat (just to turn on the AUX heat) and the output temperature rose to 85 degrees. Are these output temperatures normal? I am pretty sure that the output temperature varies upon how cold it is outside.
Excellent question! Yes, what happened to you is totally normal. Here’s why. Heat Pumps are really two heating systems in one. The primary is the heat pump. A heat pump is actually the same as an air conditioning system that cools your house, with one main difference…a reversing valve. The reversing vale reverses the flow of refrigerant in the heat pump to deliver warmth in the winter as opposed to coolness in the summer.
A common complaint about heat pumps is that they “blow cold air.” Typically, it is not really cold but is also not nearly as warm as what you might get from a gas or oil furnace. A heat pump operating normally will usually deliver heat at around 90 degrees or so. The fact that yours was blowing 78 probably means that it is short on refrigerant.
Now, you are probably wondering about that big boost that happened when you switched to “Auxiliary” heat. That is because the secondary heating system within a heat pump set up is a set of electric heating coils. When you turn on the “Aux” switch, you are firing up those coils giving the heat a big boost, but also more than doubling your electric consumption!
The way the heat pump system is supposed to work is that the heat pump should do most of the work to maintain the heat, but automatically bring up the electric resistant heat if the difference between thermostat setting and the room temperature is more than 2 degrees. It might also be that there is a problem with the control circuit that prevented this from happening properly.
So, now that you understand Heat Pump 101, the bottom line is that you should have it serviced by a pro. While what happened to you is normal, it sounds like some minor repair or maintenance is needed.