What is auxiliary heat?

Auxiliary Heat Explained

Auxiliary heat, also known as emergency heat or supplemental heat, is a secondary heating system in a heat pump that provides warmth when the heat pump alone cannot meet the heating demand. This typically happens when outdoor temperatures are very low (often below 30-35°F) or when the heat pump is in defrost mode.

Here's a breakdown of key aspects:

• Function: The primary role of auxiliary heat is to supplement the heat pump's output during periods of high heating demand. It kicks in when the heat pump struggles to extract enough heat from the outside air to maintain the desired indoor temperature.
• Operation: When the thermostat detects that the heat pump cannot reach the set temperature, it activates the auxiliary heat. This often consists of electric resistance heaters located within the air handler.
• Energy Consumption: Auxiliary heat is significantly less energy-efficient than the heat pump. It uses a large amount of electricity to generate heat directly, whereas a heat pump transfers existing heat.
• Cost Implications: Frequent use of auxiliary heat can substantially increase your energy bills. It's crucial to identify the root cause of its excessive activation.
• Troubleshooting: If your auxiliary heat is running frequently, it could indicate problems with your heat pump, such as a refrigerant leak, a faulty compressor, or a malfunctioning thermostat. It may also be that the heat pump is simply undersized for your home or that your home lacks sufficient insulation. Consulting an HVAC professional is recommended.
• Heat Pump Defrost Cycle: Heat pumps can ice up in cold weather. During the defrost cycle, the heat pump briefly switches to cooling mode to melt the ice. To compensate for the temporary cooling, the auxiliary heat is activated to prevent a significant drop in indoor temperature. This is a normal operation but should not be excessive.
• Minimizing Usage: To reduce auxiliary heat use, consider strategies like improving home insulation, sealing air leaks, maintaining your heat pump regularly, and setting back the thermostat when you're away from home. Sometimes, simply increasing the setpoint temperature gradually instead of drastically can prevent the auxiliary heat from engaging.