"EM Heat" is on your thermostat: why and what to do
Your thermostat says emergency heat (EM heat) because that mode is selected. Nobody else turns it on: someone picked it, often by pressing the mode button one time too many. It locks out the heat pump and heats with backup heat only, which costs more. If the heat pump works, switch the mode back to Heat.
What does "Em Heat" on the screen mean?
It means the thermostat is in a system mode, not showing a warning. Emergency heat (EM heat) is one of the modes you can choose alongside Heat, Cool, Auto and Off on a heat pump system that has backup heat. In this mode the thermostat stops using the heat pump and heats the house with the backup source alone, which is usually electric heat strips or a furnace.
Honeywell Home's wording is direct: in its Em Heat setting the compressor does not run, only the emergency heat runs. The T9 Smart user guide says the heat pump is locked out and the backup heat holds the heat setpoint. The VisionPRO TH8000 manual says the same thing in fewer words: compressor is locked out.
So the screen is telling you what you, or someone in the house, asked for. It is not a sign that the thermostat detected a fault.
How did emergency heat get turned on?
Thermostats do not switch into this mode by themselves. Google says it plainly for Nest: emergency heat must be turned on manually. The common ways it happens:
- An extra press of the mode button. On a Honeywell Home T6 Pro, the Mode button steps through every available system mode, and "Em Heat" is one of them. Stop one press early or late and the thermostat sits in EM heat instead of Heat.
- Someone turned it on deliberately, for example when the heat pump seemed to struggle, and never turned it back off. Google says a Nest keeps using emergency heat until you manually turn it off.
If auxiliary heat (AUX) is what you see instead, the thermostat is adding backup heat automatically and the heat pump is still running. That is a different situation with its own page: why a thermostat shows AUX.
What does each brand show, and how do you leave the mode?
The label and the way back differ by brand and model:
| Brand and model | What you see | How to leave it |
|---|---|---|
| Honeywell Home T6 Pro Programmable | "Em Heat" as the system mode, "Em Heat On" while it runs | Press Mode until Heat is displayed, then leave it |
| Honeywell Home T9 Smart | "Em Heat" under System mode | Menu icon, then System mode, then Heat |
| Honeywell Home VisionPRO TH8000 | "Em Heat" system setting | Press SYSTEM, choose Heat, press DONE |
| Google Nest Thermostat and Nest Learning Thermostat (4th gen) | Emergency Heat switched on in settings | On the thermostat: Settings, Emergency Heat, then turn it off. In the Google Home app: Settings, Thermostat, Emergency Heat switch |
| Google Nest Learning Thermostat (3rd gen or earlier) and Thermostat E | Emergency heat selected in the Equipment settings | Press the ring for Quick View, select the Thermostat icon, then Turn Off |
| ecobee | "Aux" system mode | Change the system mode back to Heat |
| Emerson Sensi | "Aux Heat" mode | Use the Mode button on the thermostat or the Sensi app to choose Heat |
Does it matter if emergency heat stays on?
Mainly for your bill. With the heat pump locked out, the backup heat does every bit of the heating, all day. Google describes running emergency heat as usually expensive and inefficient, and puts a number on backup heat in its Heat Pump Balance article: AUX heat can cost about 2 to 5 times as much as running the heat pump. Emergency heat uses that same expensive source with no help from the heat pump at all.
There is a second reason to switch back. Google says that needing emergency heat regularly can mean the system needs servicing. If you leave it on, you lose the chance to notice whether the heat pump is working.
When EM heat is the right choice, and when it is not, is covered in AUX heat vs emergency heat.
What should you do now?
Did someone switch it on because the heat pump stopped heating?
- Yes
Leave it on for now and arrange service with a licensed HVAC technician. Emergency heat is meant for exactly this, but it is a stopgap, not a fix.
- No
After you switch the mode back to Heat and wait about 5 minutes, does warm air start?
- Yes
It was simply left in the wrong mode. Leave it in Heat. The thermostat will bring in backup heat on its own when the heat pump needs help.
- No
Wait out any compressor protection delay first. If the screen shows no delay and still no heat arrives, check the signs at the bottom of this page.
- Yes
A short wait after you leave EM heat is normal on a heat pump, because the thermostat may hold the compressor off for a few minutes. Our page on compressor protection explains that timer.
If the emergency heat option does not appear at all, the thermostat may not be set up as a heat pump with backup heat. Honeywell says the T9 offers the mode only when the installer configured it that way, and the system type setting explains why that choice matters. On a Nest with backup heat, Heat Pump Balance controls how often the thermostat brings in AUX on its own, which is usually a better lever than reaching for emergency heat.
Frequently asked questions
- Will emergency heat turn itself off?
- No. Google says a Nest thermostat keeps using emergency heat to reach your set temperature until you turn it off by hand, and on a Honeywell Home T6 Pro the mode stays selected until you press Mode to choose another. Changing the setpoint does not end it.
- Is it harmful to leave emergency heat on?
- The manufacturers we checked do not describe it as harmful to the equipment. The cost is the issue: with the heat pump locked out, every call for heat goes to the backup heat. Google calls running emergency heat usually expensive and inefficient.
- Why is there no emergency heat option on my thermostat?
- The mode only appears when the thermostat is set up for a heat pump with backup heat. Honeywell says so for the T9, and Google says a Nest Thermostat E set up for dual fuel has no emergency heat option and switches to alternate heat by itself.
- My ecobee says "Aux". Is that the same thing?
- On an ecobee, "Aux" is the system mode that runs only the backup heat, so it does the job other brands call emergency heat. ecobee describes it as using only the furnace. If you did not choose it on purpose, set the mode back to Heat.