You should only use the emergency heat setting in true “emergency” situations, not just because it is very cold outside.
What emergency heat does
Emergency heat bypasses the outdoor heat pump and runs the backup heat source by itself (typically electric heat strips or a gas/oil furnace), which uses far more energy and costs much more to run. On most systems, the thermostat will automatically bring on auxiliary/backup heat when the heat pump struggles, so you usually do not need to switch to emergency manually.
When you should use it
Use emergency heat when:
- The outdoor unit is visibly damaged (e.g., hit by a branch, crushed, or otherwise unsafe to operate).
- The heat pump is iced over, shorting out, or simply not heating at all, and the house is getting cold.
In those cases, turning on emergency heat keeps the home warm while you wait for an HVAC technician to repair or thaw the unit.
When you should not use it
Do not switch to emergency heat just because:
- The temperature is below freezing or below 20–25°F, unless the pump is actually failing to heat.
- You think it might “help it along” or heat faster; it will usually just run the expensive backup instead of the efficient heat pump.
Because emergency heat can cost several times more per day than normal heat pump operation, it should be a short-term fallback, not an everyday cold- weather setting.
Practical rule of thumb
- Leave the thermostat on normal heat and let the system bring on auxiliary heat automatically if needed.
- Manually switch to emergency heat only if the outdoor unit is malfunctioning or unsafe, then call an HVAC professional and switch back once the heat pump is fixed and running normally.