The two thermostat labels use the same backup heat source in many systems, but they command it differently. Understanding that distinction prevents unnecessary energy use and helps you spot a heat-pump problem.
The difference at a glance
Auxiliary heat: automatic help
In normal Heat mode, the thermostat may call for backup heat when the heat pump alone cannot satisfy demand quickly enough. “AUX,” “Aux Heat,” or a similar message may appear. The heat pump usually continues operating while the backup source adds capacity.
Emergency heat: manual backup mode
Emergency Heat tells the thermostat not to use the outdoor heat-pump section. The backup source heats the home alone. That mode is for an actual outdoor-unit failure or professional direction—not routine cold weather and not a faster warm-up button.
The backup may be electric resistance heat or, in a dual-fuel system, a furnace. Equipment and thermostat controls vary, so the owner’s manual is the authority for your model.
When the Aux Heat light can be normal
- A colder-than-usual Big Country morning: the heat pump may need help meeting the load.
- A large thermostat increase: raising the setting several degrees at once can trigger backup heat.
- A defrost cycle: the outdoor coil periodically defrosts in heating mode, and auxiliary heat may temper the air indoors.
- Recovery from a setback: some controls add backup heat while restoring the scheduled temperature.
To reduce unnecessary auxiliary operation, choose a comfortable setpoint and avoid abrupt thermostat jumps. Do not sacrifice safety or comfort simply to keep the indicator off.
When should you use Emergency Heat?
Use it if the outdoor unit has clearly failed and backup heat is needed temporarily, or if a qualified technician tells you to. Examples include an outdoor fan that does not run when it should, severe mechanical noise, or a diagnosed outdoor-unit fault.
Emergency Heat is not a repair. Call for heat pump repair in Abilene and return the system to normal Heat mode once the outdoor section is safe and operational. If the outdoor unit is smoking, sparking, or repeatedly tripping a breaker, shut the system off rather than selecting another mode.
Why backup heat can use more energy
A heat pump moves heat rather than creating all of it directly. Electric resistance strips produce heat from electricity and generally use more energy to deliver the same amount of heating. Consequently, long auxiliary cycles or extended Emergency Heat operation may show up on the electric bill. Dual-fuel systems behave differently because their backup is a fuel-fired furnace.
Do not diagnose a bill from the thermostat indicator alone. Weather, thermostat habits, rates, insulation, duct leakage, and equipment condition all matter.
When the thermostat message points to a problem
Schedule service if Aux Heat remains on for long periods in mild weather, the outdoor unit never runs, the temperature keeps falling, or the system shifts to backup frequently without an obvious weather or setpoint cause. A dirty filter is one safe item to check. Beyond that, refrigerant, sensor, outdoor-coil, defrost, thermostat, airflow, and electrical faults require testing.
If the system runs but the house stays cold, follow the separate heat pump not heating checklist. Preventive inspection through heating maintenance should include the backup-heat and control sequence appropriate to the system.
Frequently asked questions
Should I switch my heat pump to emergency heat when it gets cold?
No. Leave the thermostat in normal Heat mode during ordinary cold weather. The system adds auxiliary heat automatically when needed. Use Emergency Heat only when the outdoor heat-pump section has failed or a technician instructs you to use it.
Is it normal for auxiliary heat to come on?
Yes. Auxiliary heat may run during colder weather, while the heat pump defrosts, or after a large thermostat increase. It needs attention if it stays on for long periods in mild weather, the home does not warm, or the outdoor unit never runs.
Does emergency heat cost more to run?
Often yes. Many all-electric systems use electric resistance strips for backup heat, which generally consume more electricity than normal heat-pump operation. The exact cost depends on the system, backup heat source, weather, and utility rate.
Aux Heat staying on—or outdoor unit not working?
Wright Choice can diagnose heat-pump and backup-heat operation in Abilene and the Big Country.