Emergency Heat on a Heat Pump
Emergency Heat is a thermostat/control mode that tells many heat-pump systems to use the backup heat source instead of normal heat-pump heating.
It is not a mode to select simply because the weather is cold.
The system's automatic controls should normally decide when supplemental heat is needed.
Source: Carrier - Auxiliary Heat vs. Emergency Heat
Safety: Emergency Heat is not a response to electrical hazards or fire. For smoke or suspected fire, leave the building, stay outside, and call 911 from a safe location. For burning smells, damaged wiring, or repeated breaker trips without signs of fire, stop troubleshooting; switch the thermostat Off only if safe and arrange service. Do not open cabinets, rewire controls, or bypass safeties.
Emergency Heat vs. Auxiliary Heat
Auxiliary heat
- normally turns on automatically
- supplements heat-pump output
- may operate during defrost or high load
Emergency heat
- usually selected manually
- used when normal heat-pump operation is unavailable or intentionally disabled
- can rely entirely on the backup source
When Should You Use Emergency Heat?
Use it when the equipment/installer instructions call for it, such as when the normal heat-pump system has failed and the backup heat source is safe and available.
Examples can include:
- outdoor heat-pump unit failure
- specific service instruction
- certain fault conditions
The exact behavior depends on system design.
Should You Use Emergency Heat When It Is Very Cold?
Not automatically.
Modern cold-climate heat pumps can operate at very low temperatures.
The thermostat/system should normally manage auxiliary heat based on its controls.
Selecting Emergency Heat can bypass efficient heat-pump operation and increase cost.
Why Can Emergency Heat Cost More?
If the backup source is electric resistance heat, its electrical use per unit of delivered heat can be much higher than a functioning heat pump.
A heat pump at COP 2 delivers roughly twice the useful heat per unit of electricity as resistance heat.
What If Emergency Heat Does Not Work?
If the backup heat source is expected to run but does not:
- confirm thermostat mode
- check for a visible fault code
- check whether the correct HVAC breaker has tripped
Only consider one reset if you can identify the correct HVAC breaker, the panel and surrounding area are dry, there is no smoke, burning smell, sparking, unusual heat, or visible damage, and the equipment instructions permit it. Use only the breaker handle; never remove the panel cover or open equipment cabinets. If uncertain, leave it to a qualified technician. If the breaker trips again, stop resetting it and arrange professional diagnosis.
Source: Carrier - Heat Pump Troubleshooting
Professional diagnosis may be needed.
What If Emergency Heat Is Stuck On?
Check thermostat mode first.
If the control is not intentionally in Emergency Heat and the system continues relying on backup heat, arrange service.
Possible causes include:
- control configuration
- sensor issue
- outdoor-unit failure
- other heat-pump fault
What Does Emergency Heat Use in Dual Fuel?
In a dual-fuel system, backup heat can be the furnace depending on the system/control design.
That is different from an all-electric heat pump with resistance elements.
Get Emergency-Heat Problems Diagnosed
If the heat pump is unavailable or the system will not leave Emergency Heat, have the controls and primary heat-pump equipment checked.
Understand repair costs and next steps
Review diagnosis and repair cost factors, then prepare useful observations for a qualified technician.