Emergency heat on a heat-pump thermostat is only for true backup, not for normal cold weather. Using it at the wrong time can be very expensive and may signal a problem with your system.
What emergency heat is
Emergency heat bypasses the outdoor heat pump and uses only the backup heat source (usually electric heat strips, sometimes gas/oil).
Because it skips the efficient heat pump and runs the least efficient heater by itself, it costs much more per hour than normal “Heat” or “Aux” operation.
When you should use it
You should manually switch to Emergency Heat only when the heat pump cannot or should not run, for example:
- The outdoor unit is clearly damaged (hit by a branch, crushed, leaking, making severe grinding or buzzing and not running).
- The outdoor unit is frozen solid or iced over and not defrosting, and the house is not staying warm.
In these cases, turn on Emergency Heat to stay warm and call an HVAC technician as soon as possible.
When you should not use it
Do not turn on Emergency Heat just because it is very cold outside or you think it “helps” the heat pump.
Modern heat pumps are designed to run in freezing weather and will automatically bring on auxiliary heat when needed without you using the Emergency setting.
How long to leave it on
Emergency heat should be temporary—just long enough to get through the emergency until a repair is made.
Leaving the thermostat in Emergency mode for days or weeks can dramatically increase your electric bill.
Simple rule of thumb
Use Emergency Heat only if the outdoor unit is broken, unsafe to run, or completely iced and not working, and you are waiting on service.
For everyday cold weather, leave the thermostat on regular “Heat” and let the system manage auxiliary heat automatically.
