Emergency Heat on a Heat Pump: What It Means & When to Use It
Emergency Heat is typically a manual backup-heating mode on a heat-pump thermostat. On many systems, selecting it stops normal heat-pump compressor heating and relies on the backup heat source instead.
That makes Emergency Heat different from ordinary auxiliary heat. AUX can be called automatically by the system when extra heat is needed. Emergency Heat is generally used when normal heat-pump operation is unavailable or intentionally disabled.
What Is Emergency Heat?
Emergency Heat is a backup mode available on many heat-pump thermostats. The backup source may be electric resistance heat, a furnace, or another compatible heating source depending on the system design.
Exact thermostat behavior varies, so the thermostat and equipment manuals are the final reference for your system.
When Should You Use Emergency Heat?
Do not switch to Emergency Heat simply because the outdoor temperature is below freezing. Modern heat pumps are designed to operate in cold weather, and cold-climate models are specifically built for lower temperatures.
Emergency Heat is generally used when normal heat-pump operation is unavailable or when equipment documentation or a qualified technician directs you to use the backup mode temporarily.
Emergency Heat vs. Auxiliary Heat
| Feature | Auxiliary Heat | Emergency Heat |
|---|---|---|
| How it usually starts | Automatically | Usually selected manually |
| Normal heat pump may still operate | Often yes | Often no |
| Main purpose | Supplement normal heat-pump heating | Use backup heat when normal heat-pump heating is unavailable or disabled |
| Is it normal? | Can be normal in cold weather or defrost | Should have a clear reason for being used |
For a deeper explanation of automatic backup heat, see What Is Auxiliary Heat?.
Why Emergency Heat Can Cost More
If Emergency Heat relies on electric resistance heat, operating cost can rise because resistance heat creates heat directly from electricity rather than using the heat-pump compressor to move heat.
Dual-fuel systems may use a gas or propane furnace instead, so the cost comparison depends on local electricity and fuel prices.
Compare heat-pump and furnace operating costs →
What If Emergency Heat Appears Unexpectedly?
First confirm the thermostat mode and read any error message. Thermostat labels vary, and some systems display backup heat differently from others.
If you did not intentionally select Emergency Heat and the heat pump is not operating normally, request HVAC diagnosis rather than assuming the display is harmless.
Can You Leave Emergency Heat On?
Emergency Heat may be useful temporarily when normal heat-pump heating is unavailable, but it should not become the default mode without understanding why the compressor side of the system is not being used.
If you need Emergency Heat to keep the home warm, arrange service so the underlying heat-pump problem can be diagnosed.
Should Emergency Heat Be Used During Very Cold Weather?
Not automatically. The system’s normal controls should manage heat-pump operation and backup heat according to how the equipment was designed and configured. Manually selecting Emergency Heat solely because the forecast is cold can bypass normal heat-pump operation unnecessarily.
Emergency Heat in a Dual-Fuel System
In a dual-fuel system, the backup source is typically a furnace. The system can use the heat pump under selected conditions and switch to the furnace according to the control strategy.
Read the separate Dual Fuel Heat Pump guide for how a heat pump and furnace work together.
When Emergency Heat Indicates a Repair Need
- The heat pump will not run in normal HEAT mode.
- The thermostat shows Emergency Heat unexpectedly.
- The home cannot maintain temperature even with backup heat.
- The outdoor unit is heavily iced.
- A breaker trips repeatedly.
- There is new grinding, screeching, banging, or repeated buzzing.
- The thermostat displays an error code.
If there is smoke, active sparking, fire, a gas odor, or a carbon monoxide alarm, treat that as a safety issue rather than ordinary HVAC troubleshooting.
Emergency Heat FAQs
What does Emergency Heat mean on a thermostat?
It generally means the thermostat is using the system’s backup heating source instead of normal heat-pump compressor heating.
When should I turn on Emergency Heat?
Use it according to your thermostat/equipment instructions or professional guidance when normal heat-pump operation is unavailable or intentionally disabled.
Does Emergency Heat cost more?
It can, especially when the backup source is electric resistance heat. The actual cost depends on the backup source and local energy prices.
Is Emergency Heat the same as AUX heat?
No. AUX is normally supplemental heat that may come on automatically. Emergency Heat is generally a separate manual backup mode.
Should I use Emergency Heat below freezing?
Not just because temperatures are below freezing. Heat pumps are designed to operate in cold weather, and normal system controls should manage backup heat according to the equipment configuration.
Sources
Need Heat Pump Service in Eldora, IA?
If you are relying on Emergency Heat because normal heat-pump heating is unavailable, include the thermostat message, outdoor temperature, equipment type, and any ice, noise, breaker, or error-code information when requesting service.