Heat Pump Emergency Heat vs. Auxiliary Heat
What’s the Difference?
Both Emergency Heat and Auxiliary Heat (Aux Heat) are backup heating modes used in heat pump systems, typically during very cold weather when the heat pump alone can’t keep up.
- Auxiliary Heat automatically turns on when the heat pump can’t maintain the desired indoor temperature. It works alongside the heat pump and is usually electric resistance heating. It is common to smell the dust burning from these heaters during the season’s first operation.
- Emergency Heat is a manual setting on your thermostat. When activated, it shuts off the heat pump entirely and uses only the backup heat source. It’s intended for emergencies—like when the heat pump is damaged or not functioning. Make sure you only use this setting if there is a known issue with your heat pump, as it is a much more expensive heating method; hence the name “Emergency Heat”!
Heat Pump Defrost Cycle – What Happens and Why
During cold weather, moisture in the air can freeze on the outdoor coil of a heat pump, forming frost or ice. This buildup reduces efficiency and airflow. To fix this, the heat pump goes into a defrost cycle:
- Reverses operation – temporarily switches to cooling mode to warm the outdoor coil. During this switch, you may hear a loud “swoosh”.
- Outdoor fan stops – to help heat the coil and thaw any ice faster. You may also notice steam rising from the unit. That tells us it is working!
- Auxiliary heat turns on inside – to keep the home warm during defrost. However, air temperatures may not be as warm as normal during this time. Once the frost melts, the system switches back to normal heating operation. You may notice moisture in or around your unit after a defrost cycle. A defrost cycle could initiate every hour in extreme cold weather conditions.
