When to Switch to Emergency Heat on a Heat Pump

Heat pumps provide efficient heating for many American homes, but recognizing when to engage emergency heat ensures comfort and protects equipment. This guide explains the signs, causes, and steps for switching to emergency heat, helping homeowners make informed decisions about system operation and energy costs.

Situation	Indicator	Action
Outdoor Unit Icing	Visible ice buildup despite defrost cycle	Consider emergency heat and call a technician
Weak Indoor Heat	Room temps drop; compressor runs without warm air	Switch to emergency heat temporarily
Compressor Fault	Error codes or no compressor activity	Use emergency heat and schedule repair
Extreme Cold	Prolonged subfreezing temps below manufacturer guidance	Use emergency heat sparingly to maintain warmth

How Heat Pumps And Emergency Heat Work

Heat pumps move heat between indoors and outdoors using a compressor and refrigerant, functioning as both heater and air conditioner. In cold conditions, the outdoor coil may struggle to extract heat, and frost buildup can occur. Emergency heat is an auxiliary electric or gas heating mode that bypasses the heat pump’s outdoor unit to provide direct heat when the primary system fails or cannot keep up.

Common Reasons To Use Emergency Heat

Homeowners may need to switch to emergency heat for several practical reasons. Recognizing these situations helps prevent discomfort and system damage.

System Malfunction Or Compressor Failure

If the heat pump compressor is not running due to electrical faults, control board errors, or mechanical failure, the heat pump cannot move heat. Emergency heat ensures continued warmth until repairs are completed.

Insufficient Heat During Extreme Cold

Heat pumps have decreased efficiency at very low outdoor temperatures. When outdoor temperatures fall below the unit’s effective range, the system may run continuously without reaching setpoint. Emergency heat supplements warmth in these scenarios.

Defrost Or Icing Problems

Heat pumps enter defrost cycles to melt ice on outdoor coils. Persistent icing despite defrost cycles or a stuck defrost control can reduce heating capacity. Engaging emergency heat prevents indoor temperature drops while diagnosing the issue.

Thermostat Or Control Settings

Incorrect thermostat configuration or failed sensors can cause the heat pump to operate improperly. Some thermostats display an “Emergency Heat” or “Aux Heat” option; using it can stabilize indoor temperatures during troubleshooting.

Signs That Indicate Switching To Emergency Heat

Understanding specific indicators enables timely action. The following signs suggest switching to emergency heat or calling a professional.

• No Warm Air: Air from vents remains cool while the heat pump runs.
• Outdoor Unit Loud Or Silent: Unusual noise or complete lack of compressor sound.
• Frequent Short Cycling: System rapidly turns on and off, indicating control or component issues.
• Constant Defrosting: Repeated defrost cycles or visible ice that does not clear.
• Thermostat Error Codes: Diagnostic codes indicating outdoor unit faults or low refrigerant.

How To Safely Switch To Emergency Heat

Switching to emergency heat is straightforward but should be done with understanding. Follow these steps to ensure safety and avoid unnecessary energy waste.

1. Locate The Thermostat Setting: Most modern thermostats have a mode selector showing Heat, Cool, Auto, and Emergency Heat (E or Aux).
2. Switch To Emergency Heat: Change the mode to Emergency Heat or Aux Heat. This disables the outdoor compressor and activates the auxiliary heating element or gas furnace.
3. Monitor Indoor Temperature: Allow the system to work and check that indoor temperatures stabilize. Emergency heat heats more slowly but directly.
4. Call A Technician: Arrange professional service to diagnose and repair the heat pump. Emergency heat is a temporary measure, not a long-term solution.

Energy And Cost Considerations

Emergency heat is typically less efficient and more costly than the heat pump’s normal operation because it relies on electric resistance heating or a secondary fuel source. Use it only when necessary and for limited periods.

Electric resistance heat can be 2–3 times more expensive per unit of heat than a functioning heat pump. Gas auxiliary units may be cheaper than electric but still costlier than a fully operational heat pump in mild conditions.

When Not To Use Emergency Heat

Using emergency heat unnecessarily increases energy bills and can create wear on auxiliary systems. Avoid switching to emergency heat when the issue is minor or when the heat pump can recover.

• If The Heat Pump Is Starting And Warmth Returns: Wait several cycles to see if performance improves.
• During Brief Temperature Fluctuations: Short outdoor dips often correct as the system adjusts.
• If The Thermostat Is Misconfigured: Correct settings first before using emergency heat.

Troubleshooting Before Switching To Emergency Heat

Some fixes may restore normal heat pump operation without engaging emergency heat. Performing basic checks saves time and cost.

Check Power And Breakers

Confirm the heat pump’s breaker and the auxiliary heat breaker are on. Tripped breakers can disable the compressor while auxiliary heat remains available.

Inspect Outdoor Unit

Clear debris, snow, and ice around the outdoor unit. Ensure adequate airflow and remove obstructions that impede performance. Turn off power before clearing heavy ice to avoid injury.

Examine Thermostat Settings

Verify the thermostat is set to Heat and that the temperature setpoint is above room temperature. Reset the thermostat or replace batteries if the display is erratic.

Check Air Filters And Vents

Clogged filters and closed vents reduce airflow and make the system work harder. Replace filters and open supply vents to improve heat distribution.

Repair And Maintenance Steps To Prevent Emergency Heat Use

Regular maintenance reduces the likelihood of emergency heat dependence. Schedule professional service and follow manufacturer guidance.

• Annual Tune-Ups: Technicians should check refrigerant levels, electrical connections, and compressor health.
• Defrost Control Service: Ensure the defrost cycle functions correctly and sensors are calibrated.
• Clean Or Replace Filters: Regular filter changes improve efficiency and prevent indoor coil buildup.
• Inspect Outdoor Unit Placement: Keep the outdoor unit elevated and clear of vegetation and snow.

Emergency Heat And Different Heat Pump Types

Heat pump designs affect how emergency heat is provided. Understanding the system type helps homeowners choose appropriate actions.

Air-Source Heat Pumps

Most common in U.S. homes, these rely on outdoor air. Emergency heat typically uses electric resistance strips or a gas furnace if the home has a dual-fuel system.

Ground-Source (Geothermal) Heat Pumps

Less affected by outdoor air temps, geothermal systems rarely need emergency heat. If auxiliary heating is present, it usually serves as a backup during service events.

Mini-Split Heat Pumps

Some ductless mini-splits include auxiliary electric heat in indoor units. Emergency heating options depend on model and thermostat capabilities.

How Long Can Emergency Heat Be Used

Emergency heat can be used for short to moderate durations while waiting for repairs, but it is not intended for continuous long-term use. Prolonged reliance increases operating costs and wear on auxiliary components.

As a guideline, emergency heat is suitable for hours to days while repairs are arranged. If the primary heat pump is down for longer, homeowners should consult an HVAC professional to evaluate options and potential temporary alternatives.

When To Call An HVAC Professional

Professional diagnosis should occur when the heat pump shows persistent failure signs or when switching to emergency heat becomes frequent. Technicians can perform electrical, refrigerant, and mechanical checks safely.

• Outdoor compressor does not start despite power present.
• Visible refrigerant leaks or oil stains near the unit.
• Recurrent ice buildup that bypasses defrost cycles.
• Thermostat error codes or repeated short cycling.

Best Practices For Homeowners

Adopting a few habits reduces emergencies and improves heat pump longevity.

• Schedule annual professional maintenance before winter. Early service reduces winter breakdowns.
• Monitor system performance and address small issues promptly.
• Keep the outdoor unit clear of snow and debris, especially during storms.
• Understand thermostat modes and when to use Emergency Heat responsibly.

Key Takeaways

Emergency heat is a temporary backup, not a replacement. Use it when the heat pump fails, during extreme cold when the pump cannot keep up, or when defrosting/icing issues persist. Homeowners should troubleshoot basic issues first, monitor energy costs, and schedule professional repairs to restore efficient operation.

For safe operation, follow manufacturer instructions and consult a licensed HVAC technician for persistent or complex problems.