When Does a Heat Pump Switch to Emergency Heat and How to Manage It

A heat pump switches to emergency heat when outdoor temperatures drop below the system’s effective operating range or when the heat pump cannot maintain the indoor setpoint. This article explains typical switch temperatures, factors that influence the changeover, how thermostats and backup heat sources work, cost implications, and best practices for homeowners to manage emergency heat efficiently.

Item	Typical Range
Common Switch Temperature (Balance Point)	20°F to 35°F
Thermostat Default Emergency Heat Trigger	Manual Or Based On System Failure
Backup Heat Types	Electric Resistive Heat, Gas Furnace, Dual-Fuel Systems
Energy Cost Comparison	Emergency Heat Often 2–4× More Expensive Than Heat Pump Mode

How Heat Pumps Heat And When Emergency Heat Is Used

Heat pumps move heat from outdoors to indoors using refrigerant and a compressor. They are efficient until outdoor air is very cold. As temperatures fall, the heat pump’s capacity to extract heat declines, increasing run times and reducing the ability to maintain the thermostat setpoint.

Emergency heat is auxiliary heating engaged when the heat pump cannot meet demand or is inoperable. This mode relies on backup heating—typically electric resistance strips, a fossil-fuel furnace in dual-fuel setups, or a separate backup heat source—rather than the heat pump’s compressor.

Typical Temperatures That Trigger Emergency Heat

There is no single fixed temperature when a heat pump switches automatically to emergency heat; the switch depends on several variables including system design, thermostat programming, and homeowner choices.

Industry practice identifies a practical range known as the balance point, where the heat pump’s output equals the home’s heat loss. For many U.S. homes, this balance point falls between 20°F and 35°F. Below the balance point, auxiliary heat is often required to maintain setpoint.

Factors That Determine The Balance Point

• Climate Zone: Colder climates push the balance point higher because demand is greater and less heat is available outdoors.
• Heat Pump Size And Efficiency: Higher-capacity or cold-climate heat pumps can operate effectively at lower temperatures.
• Home Insulation And Airtightness: Well-insulated homes have lower heat loss, lowering the balance point.
• Thermostat Setpoint: A higher indoor setpoint moves the balance point to a warmer outdoor temperature.
• Supplemental Heat Type: Electric resistance vs. gas furnace influences when and how the system uses backup heat.

Thermostat Controls: Emergency Heat vs. Auxiliary Heat

Consumers often confuse the thermostat settings. Auxiliary (aux) heat runs automatically when the thermostat determines supplemental heat is needed. Emergency heat is a manual setting used when the heat pump fails or during service; it forces backup heat and typically disables the heat pump to avoid damage.

Modern smart thermostats and two-stage systems can manage supplemental heat dynamically, engaging electric strips or a furnace only when required. Thermostats rarely switch to emergency heat automatically unless configured by the installer or set manually by the user.

How Dual-Fuel Systems Work

Dual-fuel systems combine a heat pump with a gas or oil furnace. The control strategy typically switches between heat pump and furnace at a preset temperature or based on efficiency calculations.

In this configuration the furnace takes over below a predetermined outdoor temperature—often in the 25°F to 40°F range—because the furnace becomes more economical and capable of meeting heating loads at severe cold.

Energy And Cost Implications Of Emergency Heat

Emergency heat, especially electric resistance, is substantially less efficient than a functioning heat pump. Electric strips convert electricity to heat at nearly 100% efficiency but deliver far fewer BTUs per kWh relative to the heat pump’s coefficient of performance (COP).

As a result homeowners often see utility bills spike when emergency heat runs. It is common for emergency heat to cost 2 to 4 times as much as operating the heat pump, depending on local electricity and gas rates and system efficiencies.

How To Tell If The System Switched To Emergency Heat

Signs that a heat pump has switched to emergency or auxiliary heat include a sudden increase in electricity consumption, the outdoor unit stopping, warmer air from vents without the compressor running, or a thermostat displaying an emergency heat icon.

Homeowners should check the thermostat mode and outdoor unit operation. If the outdoor unit is off while indoor heat continues and bills rise, the system may be in emergency heat.

When Emergency Heat Is Appropriate

Emergency heat is appropriate when the heat pump is broken or during extreme cold if the system control calls for backup. It is not intended as a regular operating mode because of high energy cost.

If the heat pump cannot maintain setpoint due to a malfunction, manually switching to emergency heat can restore indoor comfort while waiting for repair.

How To Manage And Minimize Emergency Heat Use

• Improve Home Efficiency: Upgrade insulation, seal air leaks, and add weatherstripping to reduce heat loss and lower the balance point.
• Lower Thermostat Setpoints: Reduce the setpoint by a few degrees during cold snaps to keep the heat pump in charge longer.
• Use Smart Thermostats: Install thermostats with outdoor temperature sensors and optimized staging to delay auxiliary heat until truly necessary.
• Maintain The System: Regular HVAC maintenance, refrigerant checks, and timely repairs help the heat pump operate reliably in lower temperatures.
• Consider Cold-Climate Heat Pumps: Newer models designed for cold climates maintain capacity at lower temperatures, reducing reliance on backup heat.

Testing Emergency Heat And Troubleshooting

To test emergency heat, switch the thermostat to the emergency heat setting while monitoring the outdoor unit and indoor airflow. The outdoor compressor should remain off and the backup heat should energize.

If the system fails to heat in emergency mode, investigate electrical panel breakers, thermostat wiring, and the backup heat source. Consult an HVAC professional for diagnostics if the issue persists.

Safety Considerations

Emergency heat often involves electric resistance or fuel-burning appliances. Ensure smoke and carbon monoxide detectors are functional when using fossil-fuel backup systems.

Avoid manual switching to emergency heat as a long-term solution. Prolonged operation can stress electrical circuits and increase fire risk if wiring or components are outdated.

How Installers Set Changeover Temperatures

Installers use manual calculations and manufacturer recommendations to program changeover points. They consider equipment capacity, home heat loss, and local climate data to set a sensible balance point or control algorithm.

Some systems use outdoor sensors and algorithms to calculate the optimal switch based on real-time performance rather than a fixed temperature, improving efficiency and comfort.

Common Myths And Clarifications

• Myth: Emergency heat automatically engages at a specific temperature on all systems. Fact: There is no universal auto-trigger; behavior depends on system design and thermostat settings.
• Myth: Emergency heat is always the same as auxiliary heat. Fact: Emergency heat is a manual override; auxiliary heat can operate automatically as needed.
• Myth: Using emergency heat saves the heat pump. Fact: Emergency heat is for temporary use; regular maintenance protects the heat pump more effectively.

Practical Recommendations For Homeowners

• Monitor outdoor temperatures and understand the system’s balance point. Expect auxiliary heat use commonly below 20–35°F.
• Install a smart thermostat with outdoor sensing and staging controls to minimize unnecessary emergency heat use.
• Schedule annual HVAC maintenance before the heating season to ensure the heat pump performs well in cooler weather.
• Consider upgrading to a cold-climate or variable-speed heat pump for better low-temperature performance.
• If energy bills rise unexpectedly, check whether the system is operating in emergency heat and call a licensed technician for inspection.

FAQ

Will My Heat Pump Always Use Emergency Heat Below A Certain Temperature?

No. Many heat pumps continue to operate efficiently at low temperatures, especially modern cold-climate models. Emergency or auxiliary heat engages based on capacity relative to demand and thermostat control logic.

Is Emergency Heat The Same As Backup Heat?

Emergency heat refers specifically to the thermostat setting that forces backup heat and typically disables the heat pump. Backup or auxiliary heat is the system component that provides supplemental heat, which can operate automatically.

How Much More Does Emergency Heat Cost?

Costs vary, but electric resistance emergency heat can be 2 to 4 times more expensive than heat pump mode, depending on electricity rates and the heat pump’s COP.

Should A Homeowner Set The Thermostat To Emergency Heat During A Cold Snap?

Only if the heat pump cannot maintain comfort or is malfunctioning. Using emergency heat as a primary heating method increases costs substantially.

When To Call A Professional

If the heat pump frequently fails to maintain temperature at mild outdoor temperatures, the system trips into emergency heat often, or the outdoor unit shows abnormal behavior, contact an HVAC technician. Persistent reliance on emergency heat indicates an underlying issue that requires diagnosis.

Technicians can check refrigerant charge, compressor health, reversing valve operation, and thermostat configuration to restore efficient operation.

Key Takeaways

Balance point typically occurs between 20°F and 35°F depending on system and home characteristics. Thermostats can differentiate auxiliary and emergency heat modes, and emergency heat is more costly. Home efficiency improvements, proper maintenance, and modern heat pump technology reduce the need for emergency heat while protecting comfort and energy budgets.