When Should I Use Emergency Heat?

What Emergency Heat actually does

A heat pump normally moves heat from the outdoor air into the house. On a cold day it may run longer because there is less heat available outside and the home is losing heat faster.

That alone is not a reason to change modes.

When you select Emergency Heat, the thermostat stops calling for normal heat-pump heating and makes the secondary source responsible for the heat. Depending on the equipment, that source may be electric resistance strips, a furnace in a dual-fuel system, or another installed backup.

It can protect comfort during a breakdown, but it remains a temporary operating mode.

• It disables normal heat-pump heating.
• It uses the system's installed secondary heat source.
• Backup heat may be electric, gas, oil, or another configured source.
• It keeps the house warm while the primary problem is diagnosed.

When should you switch it on?

Use Emergency Heat when there is evidence that normal heat-pump heating is unavailable. Examples include an outdoor unit that has stopped because of a confirmed failure, a heat pump that will not produce heat after safe basic checks, or a technician who tells you to use backup mode until the repair is complete.

Do not choose it just because the night is cold. If the indoor temperature is holding near the set point, warm air is moving, and the thermostat is controlling AUX Heat on its own, leave the system in normal Heat.

• The outdoor unit will not run during a normal request for heat.
• The house keeps losing temperature while the thermostat asks for heat.
• The heat pump will not produce heat after safe observations.
• A service professional recommends backup mode until repair.

Emergency Heat vs. Auxiliary Heat

AUX Heat and Emergency Heat may use the same backup equipment, but they are different thermostat commands. AUX Heat turns on automatically when the heat pump needs temporary help, such as during very cold weather, a large temperature recovery, or an outdoor-coil defrost cycle.

The heat pump usually continues operating.

Emergency Heat is selected manually. It stops depending on the outdoor heat pump and places the heating load on the backup source.

A brief AUX Heat message does not prove that anything is broken; using Emergency Heat on a working system can remove the more efficient heat pump from the job.

• AUX Heat: automatic support while the system manages a heating demand.
• Emergency Heat: manual backup mode when normal heat-pump heating is unavailable.
• AUX Heat can be normal during cold weather or defrost.
• Emergency Heat usually costs more and calls for diagnosis.

What should you check before changing modes?

Start with what the home is doing. Is the indoor temperature slowly rising, holding steady, or continuing to fall?

Then read the complete thermostat display. AUX Heat means the controls called for help; Emergency Heat or EM Heat usually means the manual mode was selected.

An error message or blank display points to a different troubleshooting path.

Make only safe observations. Confirm the thermostat is set to Heat and above the room temperature, check for a visibly clogged filter, and see whether air is moving from the supply vents.

Look at the outdoor unit from a safe distance and note whether it is running, silent, unusually loud, or blocked by debris.

• Let a normal defrost cycle finish if the unit briefly produces steam or changes sound.
• A light coating of frost can be normal before defrost; heavy ice that will not clear needs service.
• Note a tripped breaker, but do not keep resetting one that trips again.
• Do not remove thermostat wires, open equipment, or change installer settings.

How long can Emergency Heat run?

There is no single safe number of hours for every heat pump and backup system. Emergency Heat can run while the backup equipment operates within its design, but treat the setting as a short-term bridge to diagnosis.

Electric resistance backup often costs more than normal heat-pump operation, and continued use can hide a compressor, refrigerant, control, airflow, or outdoor-unit problem.

Watch the indoor temperature and airflow while backup mode is on. If the house continues to cool, the backup source cannot maintain a safe temperature, or vulnerable people or plumbing are at risk, arrange faster help and protect them while you wait.

• Emergency Heat is needed more than occasionally.
• The indoor temperature keeps falling even with backup mode selected.
• AUX Heat stays on for long periods during mild weather.
• The outdoor coil remains heavily iced after a reasonable defrost period.
• The system develops grinding, banging, electrical, or refrigerant-like hissing sounds.

What should Frederick County homeowners do next?

If the heat pump is warming the home and the thermostat only shows AUX Heat briefly, leave the system in normal Heat and let its controls stage the backup source. If normal heating has failed, select Emergency Heat only if your system supports it, then arrange heat-pump diagnosis.

Do not treat the setting as a seasonal mode for January weather.

Before the repair visit, write down the thermostat message, indoor and outdoor temperatures, when the problem began, whether the outdoor unit runs, and whether Emergency Heat maintains the room temperature. Those details give the technician a cleaner starting point and help restore normal heating sooner.

• Turn the manual backup mode off after the primary system is repaired.
• Arrange diagnosis when Emergency Heat is the only thing keeping the house warm.
• Leave immediately for burning smells, smoke, sparking, or another safety hazard.
• Call the appropriate emergency professional from a safe location when there is a fire or electrical danger.