Back to Blog

Why Is Your Heat Pump’s Auxiliary Heat Turning On?

post img

If you have a heat pump installed in your San Antonio-area home, you may have noticed an “aux heat” message displayed on your thermostat. While auxiliary heat is a normal function of a heat pump, it’s important to understand why it turns on and when it may indicate an issue.

In many cases, seeing auxiliary heat activate is completely normal, but if it runs too frequently or unexpectedly, it could point to a problem with your system.

In this comprehensive guide, the comfort specialists at Damiani’s Comfort Design explain auxiliary heat, when it turns on, and how to tell if there’s an issue.

What Exactly Is Auxiliary Heat?

Auxiliary heat is a backup heating system that activates when your heat pump struggles to maintain your home’s temperature. Heat pumps are designed to work efficiently by transferring heat from the outside air into your home; however, they work more gradually than traditional furnaces. When the outside temperature drops suddenly or the system needs to heat your home more quickly, auxiliary heat kicks on to help expedite the process.

Most heat pumps rely on electric resistance heating coils as the auxiliary heat source. These coils warm the air more quickly but use significantly more energy than the heat pump itself. That’s why frequent or prolonged use of aux heat can lead to higher energy bills.

When Will Your Heat Pump Switch to Auxiliary Heat?

There are several instances when your heat pump may switch to aux heat mode, including:

Freezing Temperatures

When temperatures drop below freezing, your heat pump may struggle to extract enough heat from the outdoor air. To compensate, the system turns on auxiliary heat to maintain a comfortable indoor temperature. This is expected and ensures your home remains warm on the coldest days of the year.

Thermostat Settings

Heat pumps are designed for gradual heating, so sudden increases in temperature may cause the auxiliary heat to engage to help you reach the desired temperature faster. To avoid unnecessary energy use, it’s best to adjust your thermostat gradually.

Defrost Mode

Heat pumps occasionally go into defrost mode to prevent ice buildup on the outdoor unit. When this happens, the system temporarily stops heating and switches to aux heat to maintain indoor comfort. This is a normal part of heat pump operation and should only last a short time.

Emergency Heating

Most thermostats have an “emergency heat” setting that manually activates the auxiliary heat system. This setting is meant to be used only if your heat pump is malfunctioning or unable to generate enough heat. If you accidentally turn this on, your system will bypass the heat pump entirely and rely solely on the auxiliary heating elements, leading to significantly higher energy costs.

How To Tell if Your Aux Heat Is Faulty

Auxiliary heat should only activate in the above scenarios. However, if you notice that aux heat is running more frequently than expected or doesn’t turn off, your system may have an issue. Below are a few indicators that something is wrong with your heat pump:

  • Aux heat runs even when it’s warmer than 35º F: If aux heat activates when outdoor temperatures are mild, your heat pump may not be functioning efficiently.
  • Aux heat doesn’t turn off when the thermostat is lowered: Your system should respond to thermostat adjustments. If lowering the temperature doesn’t turn off the aux heat, there may be a wiring or control issue.
  • The defrost light remains on: If your heat pump remains stuck in defrost mode, it may indicate a sensor or control problem that requires professional repair.

Call Damiani’s Comfort Design for Heat Pump Inspection & Repairs

If your heat pump’s auxiliary heat is turning on too often or not turning off properly, it may be time for an inspection. Our team can diagnose and repair any issues with your heat pump, ensuring it operates efficiently throughout the colder months.

Proudly delivering prompt, professional, efficient solutions to families throughout Northern San Antonio, Damiani’s Comfort Design is committed to keeping your home comfortable when you need it most.

Book heat pump repair in San Antonio, Texas, by contacting our team online today!

Get your system up to speed for summer $119 Damiani's Deluxe AC Tune-Up
Expires 03/31/25
Cannot be combined with other offers.
New system with payments as low as $109/month
Expires 03/31/25
With approved credit.
Any Repairs 10% Off
Expires 03/31/25
Cannot be combined with other offers.
Awesome Manufacturer Rebates - Select Systems Up to $500
Expires 03/31/25
Cannot be combined with other offers.
Second Opinion On Both Repairs And Installations Free
Expires 03/31/25
Cannot be combined with other offers.
  • Flexible financing available
  • Schedule Your Free Estimate Today!

    Free Estimate Today

    truck m_truck

    Comfort Club Plans

    Routine maintenance on your HVAC system
    can prolong the life of your current unit
    and help reduce the possibility of
    breakdowns.

    • No waiting
    • Save more
    • Hassle-free repairs
    • Trustworthy services
    • Emergency help
    • Membership discounts
    Learn More