Emergency Heat for Heat Pumps: When to Use It and How It Works

Heat pump systems include an Emergency Heat setting for use when the primary heat pump can’t effectively heat a home. This article explains what emergency heat is, how it differs from auxiliary heat, when to use it, the costs and risks, and troubleshooting steps to restore normal heat pump operation.

Feature	Emergency Heat	Normal Heat Pump
Primary Use	Backup heating when heat pump fails	Regular heating with high efficiency
Heat Source	Furnace or electric resistance	Refrigerant-based heat transfer
Energy Cost	Higher	Lower (more efficient)
Activation	Manual switch on thermostat	Automatic or thermostat-controlled

What Emergency Heat Means On A Heat Pump

Emergency Heat is a thermostat mode that disables the heat pump compressor and forces the HVAC system to use an alternate heating source, typically a gas furnace or electric resistance coils. It is intended for short-term use when the heat pump cannot operate or when outdoor conditions prevent effective heat extraction.

The function is different from the heat pump’s normal operation: while the heat pump moves heat from outdoors to indoors, emergency heat relies solely on internal heating elements or a backup furnace, making it less energy-efficient but reliable.

Emergency Heat Versus Auxiliary Heat

Many users confuse Emergency Heat with Auxiliary Heat (also called “Aux Heat” or “Backup Heat”). Both involve supplemental heating, but they differ in purpose and typical activation.

• Auxiliary Heat: Automatically activates when the heat pump cannot meet thermostat demand, such as during rapid temperature drops or defrost cycles.
• Emergency Heat: Manually selected when the heat pump is inoperable or being serviced; it keeps the home warm while the compressor is offline.

Understanding this distinction helps homeowners avoid unnecessary energy costs by only using Emergency Heat when appropriate.

When To Use Emergency Heat

Emergency Heat should be used in specific scenarios: when the outdoor unit is frozen, the compressor or reversing valve has failed, the system is under repair, or a freeze fault prevents the heat pump from producing heat.

Examples of appropriate use include: persistent indoor temperatures below setpoint despite running the heat pump, visible ice buildup not resolved by defrost cycles, or a confirmed compressor motor failure diagnosed by a technician.

How Emergency Heat Is Activated

Most thermostats with Emergency Heat have a dedicated setting labeled “EMER,” “EM,” or “Emergency Heat.” Switching to this mode typically disables the heat pump’s compressor and engages the backup heating source.

Some smart thermostats may require setup for Emergency Heat to function correctly. Installing or programming the thermostat should follow the manufacturer’s instructions to ensure the emergency mode controls the correct equipment.

Costs And Efficiency Implications

Emergency Heat is more expensive to run than the heat pump because electric resistance heaters and furnaces convert fuel to heat at lower overall efficiency than a heat pump’s heat transfer method.

Running Emergency Heat can increase utility bills substantially. Homeowners should use it only when necessary and for as short a time as possible, and schedule repairs promptly to restore the heat pump’s efficient operation.

Common Causes That Trigger Emergency Heat Use

Several mechanical or environmental issues can necessitate Emergency Heat: compressor failure, refrigerant leaks, damaged reversing valves, failed defrost cycles causing heavy icing, or electrical faults that prevent outdoor unit operation.

Regular maintenance can reduce these risks. Annual inspections, refrigerant checks, and cleaning coils and filters help prevent many conditions that lead to Emergency Heat use.

Troubleshooting Before Switching To Emergency Heat

Before manually switching to Emergency Heat, basic troubleshooting can often restore normal operation: check circuit breakers, ensure outdoor unit power switches are on, replace clogged filters, and clear debris around the outdoor unit.

1. Verify thermostat settings and mode.
2. Inspect outdoor unit for ice or debris.
3. Check indoor air handler and change filters.
4. Reset breakers for both outdoor and indoor units if tripped.

If these steps don’t resolve the issue, switching to Emergency Heat is reasonable while awaiting professional service.

Safety And Operational Considerations

Emergency Heat can involve high-current electric elements or a gas furnace. Ensure adequate ventilation for combustion appliances and check for unusual odors, which could indicate a safety issue.

Do not run Emergency Heat if a gas appliance shows signs of carbon monoxide problems; if suspected, evacuate and call emergency services. Carbon monoxide detectors should be installed and maintained in homes with combustion backup heat.

How Technicians Diagnose Heat Pump Failures

HVAC technicians use a structured approach: visual inspection, electrical testing, refrigerant pressure checks, and component-specific diagnostics for the compressor, fans, reversing valve, and defrost controls.

Technicians may recommend repair or replacement depending on age, repair cost, and overall system efficiency. A heat pump approaching the end of its typical 10–15 year service life may be a candidate for replacement rather than repeated emergency repairs.

Preventive Maintenance To Avoid Emergency Heat Situations

Regular maintenance reduces Emergency Heat occurrences. Recommended tasks include annual professional tune-ups, seasonal coil cleaning, filter changes every 1–3 months, and keeping outdoor units clear of vegetation and debris.

Homeowners replacing thermostats should ensure compatibility with the heat pump control board and backup heating source to prevent misconfigured emergency or auxiliary heat behavior.

Smart Thermostats And Emergency Heat

Smart thermostats can optimize heating performance and alert users to abnormal system operation. Properly configured, they can prevent unnecessary auxiliary heat by learning run times, scheduling, and using outdoor temperature sensors.

However, incorrect wiring or settings on smart thermostats can inadvertently force Emergency Heat. Professional installation is recommended for complex systems to avoid misconfiguration.

Cost-Benefit Analysis: Repair Versus Temporary Emergency Heat

Emergency Heat is a temporary remedy. Homeowners should weigh the ongoing higher operating cost against repair or replacement expense.

• If repair costs are lower than replacement and the system is under 10 years old, repair is often cost-effective.
• If the system is old, inefficient, or facing major component failures, replacement with a modern heat pump may yield long-term savings and fewer emergency situations.

Key Takeaways And Best Practices

Emergency Heat exists to maintain indoor comfort when the heat pump is nonfunctional, but it should be a temporary solution due to higher energy costs and potential safety considerations.

Homeowners should perform simple troubleshooting before engaging Emergency Heat, schedule prompt professional service if needed, and prioritize preventive maintenance to reduce the likelihood of emergency situations.

Resources And Further Reading

Trusted sources for more information include the U.S. Department of Energy on heat pumps, the Air Conditioning Contractors of America for maintenance guidance, and specific equipment manufacturers for model-specific emergency heat instructions.

Contacting a licensed HVAC professional is recommended for diagnosis, repairs, or when considering system replacement to ensure safety and efficiency.