When your thermostat says “Aux Heat” or “Aux Heat On,” it’s letting you know your system has temporarily switched on a backup heat source to help your heat pump. So, what does aux heat mean in plain terms? It means your heat pump is getting a little assistance to keep your home warm.
Auxiliary heat turns on automatically when the heat pump needs help reaching the temperature you’ve set – usually during a sudden drop in outdoor temperatures or when you raise your thermostat several degrees at once. For instance, if a cold front moves through Central Texas overnight and you bump your thermostat from 66°F to 72°F in the morning, your system might not be able to keep up on its own. That’s when aux heat turns on to give it a boost.
So if “Aux Heat” appears briefly on a chilly Texas morning, don’t worry – it’s a normal sign that your system is working as intended.
Auxiliary heat activates under specific conditions—usually when:
When that happens, your thermostat will display “Aux Heat On.” This doesn’t mean something’s wrong. It simply indicates your system is temporarily using additional heating elements (like electric resistance coils or a gas furnace) to maintain comfort. Once things stabilize, it automatically reverts to standard heat pump operation.
Many homeowners mix up aux heat and emergency heat, but they’re not the same. Here’s a quick breakdown:
| Feature | Auxiliary Heat | Emergency Heat |
|---|---|---|
| Activation | Automatic | Manual |
| Role | Supports the heat pump | Replaces the heat pump |
| When to Use | Cold weather or defrost cycles | When the heat pump fails |
| Energy Use | Moderate | High |
When you switch to emergency heat, the system bypasses the heat pump entirely and relies only on the backup source. It’s an energy-intensive mode that should be used only until repairs are made.
Not at all! If you see “Aux Heat” or “Aux Heat On” on your thermostat, there’s no reason to worry—it usually means your system is working exactly as it should. Auxiliary heat turns on automatically when your heat pump needs a little help keeping up with your thermostat setting, like during a sudden cold snap or after you’ve raised the temperature several degrees.
However, if you find yourself wondering why is aux heat on for long stretches or even when it’s not that cold outside, it could be a sign your system is working harder than necessary. That might point to an efficiency issue, dirty coils, or a developing problem that needs attention.
Because auxiliary heat uses more energy than your standard heat pump cycle, frequent or extended use can also drive up your utility bills. If that happens, or if you just want peace of mind, Radiant’s HVAC experts are ready to help. We offer 24/7 emergency heating repair across Austin, San Antonio, and the Hill Country, so you’re never left in the cold.
To help prevent future issues, our Radiant Care Club members receive regular tune-ups, priority scheduling, and savings on repairs. It’s an easy way to keep your system efficient, catch small problems early, and avoid unexpected surprises when the next Texas cold front rolls through.
Avoid drastic temperature jumps. Adjust your thermostat gradually, one or two degrees at a time, or let a smart thermostat handle small, automatic changes throughout the day.
Homes with good insulation retain heat longer, meaning your system won’t have to rely on auxiliary heat as often. Sealing air leaks around windows and doors can make a big difference in both comfort and energy savings.
Routine maintenance is the easiest way to prevent unnecessary aux heat activation. When your system is clean, tuned, and fully charged, the heat pump runs more efficiently and keeps backup use to a minimum.
A professional tune-up ensures your coils, refrigerant, and defrost cycle are all working properly, especially before the first cold front of the season. Warning signs your heat pump system may need service include:
Radiant’s Care Club program makes it simple to stay ahead of heat pump maintenance. Members receive priority scheduling, seasonal tune-ups, and exclusive discounts on repairs, helping prevent breakdowns and keeping systems running strong all year long.
