Most Florida homes heat with a heat pump backed up by electric heat strips. Your thermostat uses two different labels for those strips, and the difference matters.
The difference at a glance
| Thermostat shows | Normal? | What it means |
|---|---|---|
| AUX heat on a cold night | Yes | Heat strips are helping the heat pump keep up. |
| AUX heat after you raise the setting several degrees | Yes | Strips speed things up, then shut off near your set point. |
| Emergency heat you selected | Yes | Heat strips only. Use it if the outdoor unit stops. |
| Emergency heat you didn’t select | No | The heat pump isn’t heating. Call. |
| AUX heat that never turns off on a mild day | Maybe | The heat pump may not be pulling its weight. Have it checked. |
Why heat pumps need help on cold nights
A heat pump moves heat from the outside air into your home. The colder it gets outside, the harder that job becomes.
“They’re only designed to handle temperatures down to about 32 degrees. Some of the vendors are getting them a little better, closer to about 20 degrees. But once you get down to that kind of cold, it’s very tough for a heat pump to keep up. That’s where we have the heat strips as supplemental heat, or auxiliary heat, to back up the heat pumps.”
Jason Healy, Operations Manager
The 3-degree rule
Your thermostat brings the heat strips on when the room is more than about 3 degrees below your setting, and shuts them off once it’s close.
“Any time you’re adjusting your thermostat more than 3 degrees from the set temperature, the heat strip will run. Once it gets within that 3 degrees, it shuts back off, so it’s not just continuously running.”
Jason Healy
Saving energy: heat strips draw a lot of power. Raising the thermostat about 3 degrees at a time lets the heat pump do most of the work. Raise it about 5 degrees when you want the house warm faster.
When to use emergency heat
Switch to Emergency Heat yourself only if the outdoor unit has stopped running. If the house starts warming within about 15 minutes, your backup is doing its job and you’re fine for the night. If emergency heat shows up on its own, that’s your system telling you the heat pump needs attention. Read more in Emergency heat showing on your thermostat?
Call us if
- Emergency heat appears and you didn’t set it
- AUX heat runs nonstop even on mild days
- The outdoor unit won’t run in heat mode
- The air is only lukewarm with the heat on
Not sure what your thermostat means?
Flat $129 diagnostic. Technician generally there in under two hours.
Frequently asked questions
What does AUX heat mean on my thermostat?
Your electric heat strips are running alongside your heat pump to add heat. It’s normal on cold nights or after you raise the setting more than about 3 degrees.
Is AUX heat the same as emergency heat?
No. AUX heat is the strips helping the heat pump. Emergency heat is the strips running alone, without the heat pump.
Should I turn on emergency heat when it’s cold?
Only if your outdoor unit has stopped working. Otherwise, leave the thermostat on Heat and let it use AUX heat automatically.
At what temperature does a heat pump stop keeping up?
Most are designed to work down to about 32°F, and some newer models to about 20°F. Below that, the heat strips do more of the work.
