Homeowners seeking energy-efficient heating often consider combining heat pumps with electric heating elements. But when do electric heating elements actually operate with a heat pump? This detailed guide explains their function, scenarios for activation, and the impact on comfort and energy bills. Whether troubleshooting your HVAC system or planning a new installation, learn precisely what triggers auxiliary electric heat and how to optimize your system for US homes.
Overview: Heat Pumps and Electric Heating Elements Interaction
| Component | Function | When It Operates |
|---|---|---|
| Heat Pump | Extracts heat from outside air (or ground) to heat/cool a home | Whenever outside temperature is within pump’s effective range |
| Electric Heat Strips (Auxiliary Heat) | Electrically heats air, bypassing the heat pump’s outdoor exchange | During very cold weather, system defrost cycles, or extreme demand |
How Heat Pumps Work In Residential Heating
Heat pumps use electricity to transfer heat from the outside air or ground into your home. They are most efficient in moderate climates and can also provide cooling in the summer. Using a refrigerant, heat pumps absorb warmth from outside and bring it inside, working in reverse in the summer for air conditioning.
Efficiency is highest when outdoor temperatures are above freezing. As temperatures drop, the heat pump finds it harder to extract heat and maintain the indoor setpoint efficiently.
Role Of Electric Heating Elements In Heat Pump Systems
Electric heating elements, often called heat strips or auxiliary heat, are essentially electric resistance coils installed in the air handler. They function as a backup to supplement the heat pump when it can’t meet the home’s heating demand alone.
Auxiliary electric heat comes into play under specific conditions. Unlike the heat pump, which moves heat, these elements generate heat directly, similar to a toaster or electric baseboard heater.
Triggers For Electric Heating Elements Operation
During Very Cold Weather (Below Balance Point)
Every heat pump has a performance threshold called the balance point. This is the outdoor temperature at which the heat pump can no longer pull enough heat to maintain the desired inside temperature. For most units, this is between 30°F and 35°F. When outdoor temperatures drop below this point, electric heating elements are automatically activated to compensate for the deficit.
Rapid Temperature Increase Or Thermostat Changes
If a homeowner raises the thermostat by several degrees at once, the system detects a sudden demand that the heat pump can’t quickly meet. In this scenario, electric heat strips may be activated temporarily—the system runs both the heat pump and electric elements to quickly reach the new setpoint, then reverts to just the heat pump once the temperature stabilizes.
Defrost Cycle Operation
In cold climates, the outdoor coil of a heat pump can accumulate frost, reducing efficiency. The system periodically enters a defrost cycle, reversing operation to melt the frost. During this time, the heat pump temporarily switches to cooling mode, sending cold air inside. To avoid discomfort, the electric heating elements activate to keep supply air warm until the defrost cycle ends.
Emergency Heat (Manual Activation)
Most thermostats include an emergency heat (EM HEAT) setting. This mode bypasses the heat pump entirely, relying solely on electric strips. It’s intended only for use if the heat pump is malfunctioning or during extreme cold when the pump cannot operate. Running electric heat exclusively is much less efficient and costly, so should be used sparingly.
Electric Heat Strip Sequence Of Operation: Step-By-Step
- Heat pump turns on to meet demand as long as outdoor temperature allows.
- If load increases or outside temperature drops below the set balance point, **auxiliary heat (electric heating elements) are energized** by the control board.
- During a defrost cycle, electric strips activate to keep output air comfortable.
- Once demand drops, or the temperature rises, the auxiliary heat disengages and the system reverts to heat pump-only mode.
How To Know If Electric Heating Elements Are Operating
Modern thermostats often display a visible indicator: AUX HEAT, EM HEAT, or similar, signaling that the electric strips are in use. Some units have indicator lights. Homeowners should monitor energy bills in winter—spikes can indicate frequent electric element use.
Signs of operation include:
- Thermostat displaying “AUX” or “EM HEAT”
- Short bursts of warm air during defrost cycles
- Noticeably warmer air discharge compared to regular heat pump operation
- Audible click as relays engage heating coils in the air handler
Energy Efficiency & Cost Considerations
Electric heating elements use far more electricity than heat pumps alone. Each kilowatt (kW) of electric strip heat produces 3,400 BTUs, but at a significantly higher cost per unit of useful heat than a running heat pump. As a result, limiting auxiliary heat strip operation can lead to substantial energy savings over the winter.
Newer systems use advanced controls and algorithms to minimize electric strip engagement. For homeowners seeking to cut bills, maintaining a steady thermostat setpoint and upgrading insulation can help reduce auxiliary heat activation.
Heat Pump System Types And Backup Heat Integration
Air Source Heat Pumps
Most US residential systems are air source heat pumps. These units rely predominantly on outside air and are most likely to require electric backup in subfreezing temperatures.
Ground Source (Geothermal) Heat Pumps
Geothermal systems maintain higher efficiency in extreme cold. Many geothermal setups do not require electric heating strips except in cases of mechanical failure, since the ground remains much warmer than winter air.
Dual Fuel (Hybrid) Systems
Some homes pair heat pumps with gas furnaces. In such dual fuel systems, the gas furnace takes over instead of electric strips during cold weather, providing superior efficiency and lower operating costs compared to electric backup.
Thermostat Control Of Auxiliary And Emergency Heat
Modern smart thermostats optimize when electric heating elements operate. Most thermostats control auxiliary and emergency heat independently:
- AUX HEAT AUTO: Engages automatically when needed as a supplement
- EMERGENCY HEAT: Manually selected to run backup heating only
Improper thermostat settings may cause unnecessary use of electric heat—review the manual and system programming when in doubt to avoid driving up energy usage.
Factors Affecting Electric Heat Strip Usage
Several variables determine how often and for how long electric heating elements will operate with a heat pump:
- Climate: Colder regions see more frequent auxiliary heat operation
- System Sizing: Undersized heat pumps rely on electric strips more often
- Thermostat Settings: Large setpoint jumps force auxiliary heat on
- Home Insulation: Leaky homes lose heat quickly, increasing demand on backup elements
- System Age: Older heat pumps may struggle in lower temperatures, requiring more backup heat
Best Practices To Minimize Electric Backup Heat Usage
- Set thermostat to a consistent temperature rather than large day/night changes
- Schedule professional maintenance for your heat pump system each fall
- Improve home air sealing and insulation to retain more heat and reduce demand
- Use a smart or adaptive thermostat that delays auxiliary heat activation unless truly needed
Common Questions About Electric Heating Elements And Heat Pumps
Does every heat pump have electric backup?
Most US air source heat pumps include auxiliary electric heat strips as a standard for cold weather. Some advanced units use variable-speed compressors that can operate at lower temperatures with less need for backup. Geothermal systems may not require electric elements except as a failsafe.
Is it bad if AUX HEAT comes on frequently?
Frequent operation indicates the system is struggling to keep up with demand. This could be due to unusually cold weather, poor insulation, system undersizing, or mechanical issues. If auxiliary heat runs constantly, contact HVAC service for diagnosis.
Can I turn off electric backup heat?
Most modern thermostats do not allow disabling auxiliary heat entirely as it’s needed for safe operation in emergencies. However, homeowners can reduce its use by preventing large thermostat setpoint jumps and properly maintaining their system.
How much does it cost to run electric backup heat?
Electric strips can be three to five times more expensive to run per hour than a heat pump alone. For a 10kW strip (typical size), it can cost $1.20–$1.50 per hour at $0.12–$0.15/kWh utility rates. Heavy use can significantly raise winter energy bills.
Modern Innovations For Smart Heat Pump And Electric Heating Management
New controls, smart defrost logic, and dual-fuel options are reshaping how electric heat elements and heat pumps interact. Many Wi-Fi thermostats learn your home’s patterns to minimize auxiliary engagement, and inverter compressors can continue heating efficiently at lower temperatures, delaying the need for electric strips.
Auxiliary Heat Lockout Settings
Some advanced thermostats allow programming a “lockout temperature” below which the system will not use backup heating unless absolutely unavoidable. This can cut unnecessary strip heat use.
Variable-Speed Compressors
**Modern variable-speed heat pumps** can deliver more heat at lower temperatures, reducing reliance on electric elements even further, making them ideal for northern US climates.
Key Takeaways: When Do Electric Heating Elements Operate With A Heat Pump?
- Electric heating elements activate when the heat pump can’t meet demand alone—usually during very cold weather, rapid temperature changes, defrost cycles, or if “emergency heat” is selected
- Using electric backup heat is much more costly than running the heat pump, so minimizing its use through home efficiency and thermostat control is essential
- Thermostat settings, weather, and insulation all affect how often auxiliary heat operates—smart controls and well-insulated homes can reduce electric backup reliance
- Monitor your system for signs of excessive auxiliary heat use (thermostat indicators or high bills) and consider professional evaluation or upgrades if concerned
By understanding when electric heating elements operate alongside heat pumps, homeowners can improve comfort, cut costs, and make the most of their HVAC investment in 2025 and beyond.