The short answer
Aux heat is the electric backup heat strip in your air handler. It's meant for short bursts: defrost, very cold mornings, or a big temperature change. If it runs for hours on mild days, the heat pump itself is usually not doing its job: a low refrigerant charge, a failed outdoor fan or compressor, a bad defrost control, or a thermostat that isn't set up correctly for a heat pump.
Why it matters so much here
About half the homes in York County heat with electricity, and most of those use heat pumps. A heat pump moves heat instead of making it, so it can deliver two to three times more heat per dollar than the strips. When the heat pump quits and the strips carry the load, the house may still feel warm, and the only sign is the bill.
What you can check
- Go look at the outdoor unit while the thermostat calls for heat. The fan should be running and the large copper line should feel warm. If it's silent or the fan isn't spinning, the heat pump isn't working.
- Look for ice. Light frost is normal. A thick shell of ice that never clears means the defrost system isn't working.
- Change the filter. Poor airflow makes a heat pump work harder and can trip the backup heat.
- Check your setbacks. If the thermostat drops to 62 overnight and jumps to 70 at 6 a.m., the strips will come on every morning. Try smaller changes.
- Make sure it isn't on emergency heat. "EM heat" or "emergency" on the display means the heat pump is locked out on purpose.
When to call
- The outdoor unit isn't running while the house calls for heat.
- The outdoor unit stays iced over.
- Aux heat shows constantly above about 35 degrees outside.
- You smell burning when the strips come on (a little dust smell on the first cold day is normal).
Call Thermal Services at (704) 701-6478. Catching a heat pump problem in December is a lot cheaper than finding out from the February bill.
Common questions
Is it normal for aux heat to come on?
Yes, in short bursts: during defrost cycles, on the coldest mornings, or when you raise the thermostat several degrees at once. It isn't normal for aux heat to run for hours on a 45-degree day.
Should I switch my thermostat to emergency heat when it's cold?
No. Emergency heat turns off the heat pump and uses only the electric strips, which can cost two to three times as much to run. Use it only if the heat pump has actually failed and you're waiting on a repair.
Why is my heat pump running constantly in winter?
Heat pumps are designed to run long, steady cycles in cold weather, so long run times alone aren't a problem. If the house won't hold temperature, the air feels cold, or the outdoor unit is iced over and not defrosting, it needs service.
How can I lower my heat pump bill in winter?
Keep the filter clean, keep setbacks small (2 to 4 degrees), avoid emergency heat, and make sure the thermostat is set up for a heat pump with aux-heat lockout. Sealing leaky attic ductwork also makes a big difference.