Short answer
Aux heat is electric resistance heat, and it uses far more electricity than the heat pump itself. If it's running constantly, something is making the heat pump lean on it: emergency heat left on, a thermostat set up wrong, big temperature setbacks, low refrigerant, or a failed defrost. Check the thermostat mode first, then call if aux keeps running on mild days.
How a heat pump actually heats
Upstate South Carolina is heat-pump country. A heat pump doesn't burn anything. It moves heat from the outside air into your house, the same way your AC moves heat out. That's what makes it efficient.
The catch is that it has less capacity as it gets colder outside. January lows at GSP average 32.1°F (NWS 1991–2020 normals), and on those mornings a heat pump may need help. That help is the auxiliary heat: electric heat strips in the air handler, working like a big toaster. They make heat directly from electricity, and they use a lot more of it than the heat pump does.
A little aux heat on the coldest mornings is normal. Aux heat running for hours on a mild day is not.
What's probably happening
Emergency heat was left on
Someone switched the thermostat to emergency heat (EM heat) during a cold snap and never switched it back. Now the heat pump is off and the strips are doing all the work.
The thermostat isn't set up right for a heat pump
A new or replaced thermostat set up as a regular furnace, or with the wrong aux settings, can call for the strips far too often.
Big setbacks
Turning the heat way down at night and back up in the morning often forces aux heat on to recover quickly. With a heat pump, small changes or a steady setting usually work better.
Low refrigerant or a failed defrost
A leak leaves the heat pump weak, so aux carries the load. If the defrost controls fail, the outdoor coil stays iced over and the heat pump can barely heat at all.
What's normal
Defrost cycles are normal: the outdoor unit stops, may steam, and the strips come on briefly. Air that feels cooler than a gas furnace is also normal, as long as the house holds temperature.
What you can check yourself in five minutes
- Look at the thermostat mode. If it says emergency heat or EM heat, switch it back to regular heat.
- Go outside while the heat is running. The outdoor unit should be running too. If it's silent, or buried in ice for a long time, that's a clue.
- Check the breakers for both the outdoor unit and the air handler.
- Replace the filter. Weak airflow makes the heat pump work harder.
- Clear snow, leaves, or anything blocking the outdoor unit.
- Try a steady setting instead of deep overnight setbacks for a few days and watch how often aux comes on.
When to stop and call
- Aux heat runs on mild days, or all day, with the thermostat in regular heat.
- The outdoor unit isn't running when the heat is on, or it stays covered in ice.
- A breaker trips again after one reset.
- You smell burning from the vents beyond the brief dusty smell of the first cold day. Turn it off at the thermostat and the breaker.
The sooner it's found, the fewer high bills it costs you. Call Alpine Cool at (864) 702-0777 anywhere in Spartanburg or Greenville County.
Common questions
What's the difference between aux heat and emergency heat?
They use the same electric heat strips. Aux heat comes on automatically to help the heat pump when it needs it. Emergency heat is a setting you choose that shuts the heat pump off and runs only the strips. Emergency heat is meant for when the heat pump is broken, not for everyday use.
Should I turn off aux heat to save money?
Not on your own. On the coldest mornings the heat pump may need the strips to keep up, and during defrost they keep cold air from blowing into the house. The better fix is finding out why aux is running so much.
Is it normal for my heat pump to blow steam in winter?
Yes. That's the defrost cycle. The outdoor unit reverses for a few minutes to melt frost off its coil, and you may see steam and hear a whoosh. It should go back to normal on its own.
Why does my heat pump air feel cooler than a gas furnace?
A heat pump delivers air that is warm, but not as hot as a gas furnace. It runs longer and steadier instead. If the house holds temperature, that's normal.