Understanding Heat Pump Aux Heat

Heat pumps are a popular and energy-efficient choice for heating and cooling homes. However, during the colder months, homeowners may notice their system switching to a mode labeled “auxiliary heat” or “aux heat.” This feature is essential for maintaining indoor comfort when outdoor temperatures drop, but it often raises questions about efficiency, cost, and proper use. Here’s what you need to know about how auxiliary heat works and how to manage it effectively.

Auxiliary Heat: A Secondary Heating Source

Auxiliary heat serves as a secondary source of warmth in a heat pump system. When outdoor temperatures fall low enough that the heat pump can no longer efficiently extract sufficient heat from the air, the auxiliary heating element activates automatically. This supplemental system ensures consistent comfort inside your home during cold spells. It’s designed to assist the heat pump, not replace it, so seeing “AUX HEAT” on your thermostat during colder days is normal and indicates your system is doing its job.

Triggers for Auxiliary Heat Activation

Several factors can cause the auxiliary heat to engage. The most common trigger is a significant drop in outdoor temperature typically below 30 to 35°F when the heat pump’s efficiency decreases. Other triggers include sudden thermostat adjustments, such as raising the temperature several degrees at once, or when the heat pump enters a defrost cycle to remove frost buildup on the outdoor coil. During this time, the system temporarily relies on auxiliary heat to maintain indoor comfort until the defrost process completes.

The Difference Between Auxiliary Heat and Emergency Heat

Although often confused, auxiliary heat and emergency heat serve different purposes. Auxiliary heat operates automatically alongside the heat pump when extra warmth is needed. In contrast, emergency heat is a manual setting that shuts off the heat pump entirely and relies solely on the backup heating system, typically electric resistance or gas heat. Emergency heat should only be used when the heat pump is malfunctioning, as it consumes far more energy and leads to higher operating costs.

The Cost Implications of Auxiliary Heat

While auxiliary heat ensures comfort during colder periods, it is less energy-efficient than standard heat pump operation. Because it often relies on electric resistance heating, it uses more electricity, which can raise your utility bills if it runs frequently. To minimize costs, keep your thermostat set to a steady temperature rather than making large adjustments, and make sure your home is well-insulated to reduce heat loss. Regular maintenance also helps the system operate efficiently and reduces the need for auxiliary heating.

Effective Use and Maintenance Tips

Using your heat pump wisely can reduce reliance on auxiliary heat and improve overall efficiency. Schedule professional maintenance at least once a year to keep your system running smoothly. Clean or replace air filters regularly, and ensure the outdoor unit remains clear of leaves, dirt, and snow. Installing a smart thermostat can also help optimize performance by making gradual temperature adjustments and minimizing unnecessary auxiliary heat activation.

Need Help with Your Heating System in Concord, CA?

If you’re noticing frequent auxiliary heat use or experiencing performance issues with your heat pump, the experts at Air Conditioning Systems are here to help. Our skilled technicians provide professional maintenance, repairs, and system evaluations to ensure your home stays comfortable and energy-efficient throughout the winter.

Call us today at 925-676-2103 or fill out our online form to schedule your service. Located in Concord, CA, Air Conditioning Systems is dedicated to keeping your heating system performing at its best all year long.