What Does AUX Heat Mean on My Thermostat?

Q: My thermostat says AUX heat. What does that mean?

A: If you have a heat pump system, AUX heat means the system is using auxiliary backup heat to help warm the home. This is usually an automatic function that turns on when the heat pump needs help, such as during colder weather, defrost cycles, or when the thermostat is trying to recover temperature quickly. It can be normal, but if AUX heat runs too often in mild weather, it may point to a heat pump or thermostat issue.

Common Symptoms Homeowners Notice

• The thermostat shows “AUX” or “Aux Heat”
• The system is heating, but electric bills seem higher
• The heat pump runs for a long time during colder weather
• Warm air is coming out, but the system seems to run more than usual
• AUX heat appears often even when weather is not very cold
• Home takes a long time to recover after changing the thermostat setting

Safety First

• Turn the thermostat to OFF before opening any access panels.
• Shut off the breaker if checking the filter or indoor access panel.
• Do not handle wiring, capacitors, contactors, or control boards.
• Do not force the system to run if it is tripping breakers, buzzing loudly, or shutting down repeatedly.
• If you smell burning or see damaged wiring, stop and call for service.

Quick Checks You Can Do

1. Confirm you have a heat pump: AUX heat is typically shown on heat pump thermostats, not standard furnace-only systems.
2. Check thermostat mode: Make sure it is in HEAT and not EM HEAT (Emergency Heat) unless you intentionally set it there.
3. Avoid large temperature jumps: Raising the thermostat several degrees at once can trigger AUX heat to help recover faster.
4. Check the air filter: A dirty filter can reduce airflow and make the system struggle.
5. Look at the outdoor unit: Make sure it is not blocked by debris or vegetation.
6. Listen for normal operation: If the outdoor unit is not running when heat is called, the system may need service.

What AUX Heat Actually Does

A heat pump normally heats your home by moving heat from outdoor air to indoors. When the heat pump alone cannot keep up, the system can turn on auxiliary heat to assist. In many Florida homes, this backup heat is electric heat strips inside the air handler.

Think of AUX heat as a helper, not the main heating mode. It is there to support comfort when the heat pump needs extra help.

When AUX Heat Is Normal

During colder weather

As outdoor temperatures drop, heat pumps can take longer to heat the home. AUX heat may come on automatically to assist.

During defrost cycles

Heat pumps periodically defrost the outdoor coil in heating mode. AUX heat may run during this process so the home keeps getting warm air.

After a large thermostat temperature increase

If you raise the setpoint several degrees, many thermostats call for AUX heat to warm the house faster.

After schedule setbacks

Smart or programmable thermostats often trigger AUX heat during morning recovery if the overnight temperature was set back too far.

When AUX Heat May Mean There Is a Problem

AUX heat runs a lot in mild Florida weather

If AUX heat is coming on frequently when it is not very cold, the heat pump may be underperforming or the thermostat may be set up incorrectly.

The outdoor unit is not running

If the thermostat shows AUX heat and the outdoor unit is not operating, the system may be relying too heavily on backup heat because of a fault or power issue.

High electric bills with long run times

Auxiliary electric heat usually uses more electricity than normal heat pump operation, so repeated AUX usage can raise bills.

The house still is not warming up well

If AUX heat is on and comfort is still poor, there may be airflow, thermostat, electrical, or system performance issues that need inspection.

AUX Heat vs Emergency Heat

AUX heat

Automatic backup heat that turns on to help the heat pump reach or maintain the set temperature.

Emergency Heat

A manual thermostat setting that usually shuts off the heat pump and runs backup heat only. This is typically used when the heat pump itself is not working properly and you need temporary heat until service is performed.

If you accidentally leave the thermostat in Emergency Heat, energy use can increase because the system may rely on backup electric heat instead of normal heat pump operation.

Florida Homeowner Tips for AUX Heat

• AUX heat can still appear in Florida during cold snaps, defrost cycles, or aggressive thermostat recovery
• Frequent AUX heat in mild weather is more worth investigating
• Humidity and airflow issues can make a heat pump struggle and trigger more backup heat use
• Large thermostat setbacks can cause more AUX heat usage than homeowners expect

What Beacon Usually Checks

When homeowners ask about AUX heat, our friendly technicians in yellow check whether the backup heat is operating normally or masking a performance problem.

• Thermostat settings and programming behavior
• Whether the thermostat is in HEAT or Emergency Heat mode
• Air filter and airflow restrictions
• Indoor and outdoor unit operation
• Signs the heat pump is struggling to carry the load
• Electrical and control behavior affecting backup heat operation
• Comfort and humidity clues common in Florida homes

When to Call Beacon

If AUX heat stays on for long periods, shows up often in mild weather, the outdoor unit is not running, or your electric bill jumps unexpectedly, Beacon can help diagnose what is normal versus what needs repair.

Request Service
(352) 726-7530
www.BeaconSaves.com

Prevent This Next Time

• Change filters regularly to protect airflow
• Keep the outdoor unit clear of leaves and overgrowth
• Avoid large thermostat jumps when possible
• Use reasonable schedule setbacks for heat pump systems
• Schedule routine heat pump maintenance
• Watch for repeated AUX heat in mild weather and address it early

📍 Contact Beacon Services & Appliances
📞 (352) 726-7530
🌐 www.BeaconSaves.com.