Why Does My Thermostat Say AUX Heat? A Guide for Mobile, AL Homeowners

Here on the Gulf Coast, you can need a jacket before breakfast and be back in short sleeves by lunch. On one of those chilly mornings, you might turn up the thermostat and notice two little words you haven’t seen in months: AUX HEAT.

If you have a heat pump, AUX heat means your backup heat has kicked in automatically. Seeing it briefly can be part of normal operation. If it keeps showing up on mild days or your house still won’t warm up, it’s worth finding out why.

What does AUX heat mean on my thermostat?

A heat pump normally warms your home by moving heat from the outdoor air inside. When it needs extra help, it can call for auxiliary heat. In many all-electric systems, that backup comes from electric heat strips inside the air handler. Alabama Power explains how strip heat works and why it can raise your electric bill.

You might see AUX heat when:

• It’s cold outside and the heat pump needs help keeping up.
• You turn the thermostat up several degrees at once, or your schedule does it for you.
• Your outdoor unit briefly goes through a defrost cycle.

If AUX goes away and the house reaches the temperature you set, that’s generally a good sign.

Is AUX heat the same as Emergency Heat?

AUX heat comes on automatically. On systems with an Emergency Heat setting, you select that mode manually. It typically runs the backup heat by itself and keeps the outdoor heat pump off. Keep your thermostat on regular Heat for everyday use. Emergency Heat is generally for times when the heat pump can’t operate and you need temporary backup while arranging service.

Why your power bill can go up.

Yes. If your system uses electric heat strips, they typically use more electricity to deliver the same amount of heat than your heat pump does. A brief stretch of AUX heat is one thing. If the strips run for hours at a time, that extra usage can add up.

If AUX tends to pop up right after breakfast, check your thermostat schedule. A big jump from the overnight setting to the morning setting can bring on backup heat, depending on your system. Try keeping the temperature steadier for a few days and see whether AUX shows up less often.

When to schedule a service call.

Start with what you can see. Make sure the thermostat is set to Heat, check whether the filter is visibly dirty, and jot down when AUX comes on. The outdoor temperature and whether you just adjusted the thermostat are helpful details if you end up calling for service.

It’s worth scheduling a check if AUX keeps coming on in mild weather while the thermostat setting is steady, the house can’t reach the temperature you set, or the outdoor unit stays covered in thick ice. Those clues can help a technician figure out whether the issue is with the thermostat settings, airflow, or the heat pump itself.

If you’re seeing AUX heat more often than you used to, give us a holler. We’ll check what’s bringing on the backup heat and explain what we find before any repairs. Magnolia Air Solutions serves homeowners throughout Mobile and Baldwin counties. Request heating service.

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