Heat Pump Emergency Heat vs. Aux Heat
Aux heat is backup heat your thermostat turns on automatically when your heat pump can’t keep up, such as on very cold mornings or during a defrost cycle. Emergency heat is a setting you choose yourself: it shuts off the heat pump and heats with backup heat only. Use it only when the heat pump isn’t working.
Aux Heat and Emergency Heat Are Not the Same Thing
A heat pump heats your home by moving heat from the outdoor air indoors. It works well most of the winter, but when the outdoor temperature drops, it has to work harder to pull enough heat from the cold air. That’s where your backup heat comes in, usually electric heat strips in the indoor unit.
Aux (auxiliary) heat turns on automatically. Your thermostat brings it on alongside the heat pump when the heat pump can’t keep up: on the coldest mornings, during a defrost cycle, or when you raise the thermostat several degrees at once. You don’t have to do anything, and seeing “aux heat” on the thermostat in a cold snap is normal.
Emergency heat is a mode you switch on yourself. It turns off the heat pump completely and heats your home with backup heat only. It’s meant for times when the heat pump isn’t working, so you still have heat while you wait for a repair.
Both settings use electric resistance heat, which is much less efficient than the heat pump. That’s why running on emergency heat for days can raise your energy bill.
Quick comparison
| Aux heat | Emergency heat | |
|---|---|---|
| Turns on | Automatically | Only when you select it |
| Heat pump | Keeps running | Turned off |
| Use it when | Normal cold weather and defrost | The heat pump isn’t working |
| Energy use | Higher while it runs | Highest; use short-term |
When Should You Turn On Heat Pump Emergency Heat?
Emergency heat is a stopgap, not a winter setting. Switch your thermostat to “Emergency Heat” (sometimes labeled “EM Heat”) in situations like these, then call for service.
The Heat Pump Stopped Heating
The outdoor unit isn’t running, or the air from your vents stays cool even though the system is on.
Heavy Ice That Won’t Clear
The outdoor coil is encased in ice that stays for hours, even after the system runs a defrost cycle.
Damage to the Outdoor Unit
A fallen branch, storm damage or a loud mechanical noise from the outdoor unit means it should be shut down.
While You Wait for a Technician
Emergency heat keeps your home warm until the heat pump is repaired. Switch back once it’s fixed.
Not Just Because It’s Cold
Cold weather alone is not a reason to switch. Your thermostat already brings on aux heat automatically when it’s needed.
Not Sure What to Do?
Call your local office and describe what you see. We’ll tell you whether emergency heat makes sense for now.
Request serviceWhy Is My Heat Pump Covered in Ice?
A light layer of frost on the outdoor unit is normal in cold, damp weather. Your heat pump clears it with a defrost cycle: the outdoor fan stops for a few minutes, you may hear a whoosh and see steam rise from the unit, and then it goes back to heating. Aux heat often comes on during defrost so you don’t feel cold air.
Heavy ice is different. If the coil stays coated in thick ice, ice builds up on the top or sides of the unit, or the unit never seems to finish a defrost cycle, something needs attention. Common causes include a defrost control problem, low refrigerant, a fan that isn’t running or water dripping onto the unit from a gutter.
Don’t chip or pry ice off the coil, which can damage the fins and refrigerant lines. Switch to emergency heat if your home isn’t staying warm, and call your local Ellis Air office.
Keep Your Heat Pump Ready for Winter
Regular maintenance helps your heat pump run efficiently in most weather and catches small problems before a cold snap.
- Check and change your air filter monthly
- Keep leaves, snow and debris clear of the outdoor unit
- Make sure gutters don’t drip onto the outdoor unit
- Schedule a fall checkup before the first cold front
- Cool Club members get a fall visit (September–November) and a spring visit (February–April)
More heating help
Call for Heat Pump Repair
Heat pump and heating repair is available from all three offices.
Killeen
Temple
Georgetown
All three offices are open Monday–Friday, 8 AM–5 PM. Limited after-hours slots available, call to check availability.
What is the difference between aux heat and emergency heat?
Aux heat turns on automatically alongside the heat pump when it needs help, such as in very cold weather or during defrost. Emergency heat is a setting you choose yourself; it shuts off the heat pump and heats with backup heat only.
When should I turn on emergency heat?
Turn on emergency heat only when the heat pump isn’t working: it has stopped heating, the outdoor unit is damaged, or it’s encased in ice that won’t clear. Use it until the heat pump is repaired, then switch back.
Why is my heat pump covered in ice?
A light frost is normal in cold, damp weather, and the defrost cycle clears it. Thick ice that stays for hours can point to a defrost control problem, low refrigerant, a fan issue or water dripping onto the unit, and it needs service.
When should I call for heat pump repair?
Call if the heat pump stops heating, heavy ice won’t clear, you hear loud or grinding noises, or you’ve had to run on emergency heat. Our offices are open Monday–Friday, 8 AM–5 PM. Limited after-hours slots available, call to check availability.
Heat Pump Not Keeping Up?
Limited after-hours slots available, call to check availability.
Voted Best in Central Texas 2011–2026 · Lifetime workmanship warranty · Family-owned since 1988