If you own a heat pump in Austin, you’ve probably seen the thermostat display flip to auxiliary heat on a cold morning. Many homeowners wonder what this setting means, whether it’s normal, and if it’s costing them extra money. Understanding how auxiliary heat works — and when it should or shouldn’t run — can help you keep your home comfortable without wasting energy. At Solution Finders AC & Heating, we’ve helped hundreds of Austin homeowners make sense of their heating systems, and this feature is one we’re asked about often.
What Is Auxiliary Heat?
Auxiliary heat is a backup heating source built into most heat pump systems. Under normal operation, a heat pump transfers heat from the outside air into your home, even when it’s cold outside. But when temperatures fall near or below freezing, the system may struggle to extract enough warmth from the air. That’s when auxiliary heat kicks in.
Most of the time, this backup is provided by electric resistance coils installed inside the air handler. These coils act a lot like the heating element in a toaster — they heat up quickly when electricity runs through them and provide an immediate source of warmth. The air passing over them is then blown into your home to keep it comfortable.
In short, auxiliary heat is the safety net for your heating system, ensuring you stay warm when the heat pump alone can’t handle the load.
How Does a Heat Pump Work?
To understand why auxiliary heat exists, it helps to know how a heat pump functions. Unlike a gas furnace that burns fuel, a heat pump works by moving heat rather than generating it. In heating mode, it absorbs warmth from the outside air and transfers it indoors through refrigerant lines and coils.
This process is incredibly efficient when outdoor temperatures are moderate. But as the temperature drops, there’s less heat available in the air, and the pump has to work harder. At a certain point — usually around 35°F — the heat pump becomes less effective. That’s when the thermostat signals the system to engage its secondary heating source.
When Does Auxiliary Heat Activate?
Auxiliary heat isn’t designed to run constantly. Instead, it activates only in certain situations:
During freezing weather: When cold fronts sweep through Austin and outdoor temps fall close to or below freezing, the heat pump alone may not keep up. The system automatically switches on backup heat to maintain comfort.
During large thermostat adjustments: If you raise your thermostat by several degrees at once, the system may use supplemental heating strips to warm your home faster.
During defrost cycles: Heat pumps occasionally switch into cooling mode briefly to melt ice off the outdoor coil. While that happens, the backup heat may run indoors to prevent a noticeable drop in temperature.
If auxiliary heat is running frequently on mild days, that usually indicates a problem worth addressing.
Why Auxiliary Heat Costs More
One of the main concerns about auxiliary heat is cost. Electric resistance coils require a lot of electricity compared to the efficiency of a heat pump. While a pump may produce three units of heat for every unit of energy consumed, resistance strips provide only one-to-one output.
That means every hour auxiliary heat runs, your energy use spikes. A short cycle here and there isn’t a problem, but if the system relies on it too heavily, you’ll notice higher utility bills — especially during long cold spells.
How to Reduce Dependence on Auxiliary Heat
Fortunately, there are steps homeowners can take to limit how often auxiliary heat engages:
Avoid sudden thermostat changes: Increase the temperature a degree or two at a time instead of cranking it up all at once.
Schedule professional tune-ups: A well-maintained heat pump runs more efficiently and needs less backup.
Improve home insulation: Adding attic insulation, sealing ductwork, and fixing air leaks makes it easier for your heat pump to maintain temperature.
Replace filters regularly: Dirty filters restrict airflow and force the system to work harder, often triggering backup heating.
At Solution Finders AC & Heating, we offer seasonal maintenance plans designed to keep your system efficient and minimize the use of costly backup heating.
Signs That Something May Be Wrong
Auxiliary heat is normal under the right conditions, but overuse can point to bigger issues. Watch for these warning signs:
Auxiliary or emergency heat running constantly during mild weather.
Significant spikes in your energy bills without a change in outdoor temperature.
Difficulty reaching the thermostat setting even with backup heat active.
Problems may stem from thermostat malfunctions, low refrigerant levels, clogged airflow, or even a failing heat pump. A professional inspection can pinpoint the cause.
Auxiliary Heat vs. Emergency Heat
It’s easy to confuse auxiliary heat with emergency heat, but they aren’t the same. Auxiliary heat turns on automatically when needed. Emergency heat, on the other hand, is a manual setting you can select on your thermostat.
When you switch to emergency heat, the system shuts off the heat pump completely and relies only on the electric heating strips. This should only be used if the outdoor unit is malfunctioning or frozen over. Running emergency heat unnecessarily can lead to very high energy costs.
Why Professional Service Is Essential
While homeowners can do their part with filter changes and insulation improvements, regular professional service is key to keeping auxiliary heat in check. A licensed HVAC technician can:
Test thermostat calibration.
Check refrigerant levels.
Clean and inspect coils.
Verify that backup heat only engages when truly necessary.
Solution Finders AC & Heating has the experience to keep Austin homes comfortable year-round. Our team understands the balance between efficiency and comfort, and we help homeowners get the most out of their systems without relying too much on costly secondary heating.
Final Thoughts
Auxiliary heat is a built-in backup that ensures your home stays comfortable during Austin’s coldest days. But it’s meant to be used sparingly, not as the primary heating source. By learning how it works, watching for warning signs, and keeping up with regular maintenance, you can control costs and extend the life of your system.
If you’ve noticed your thermostat displaying auxiliary heat more often than expected, don’t ignore it. Call Solution Finders AC & Heating today and let us make sure your system is running as efficiently and reliably as possible.
