Air source heat pumps have become a leading choice for home heating and cooling, offering excellent efficiency in both seasons. In heating mode, however, they face a limitation that gas furnaces do not: heating capacity drops as outdoor temperatures fall. When a heat pump cannot deliver enough warmth alone, the system activates electric resistance strip heaters to fill the gap. This arrangement creates an avoidable downside that can double or triple your heating costs if not managed properly. For a broader overview, see our article on mini split heat pumps for cold weather heating.
Understanding the Heat Pump Achilles’ Heel
Electric resistance auxiliary heat is essentially a large toaster element installed in the air stream of a heat pump system. When the compressor cannot meet the thermostat setpoint, these strip heaters activate and add extra BTUs to the supply air. The strips sit downstream of the indoor coil so hot air from the resistance elements does not blow backward over the coil and interfere with operation.
The problem is not that strip heat exists, but that it is called on too frequently or when not needed. This happens due to oversized strip heaters, incorrect thermostat settings, improperly set outdoor lockouts, and wiring errors. When strip heat runs unnecessarily, electricity bills rise dramatically with no comfort benefit. For a deeper technical look, read our technical analysis of cold climate heat pump performance.
- Electric resistance strips are typically rated between 5 kW and 20 kW, consuming substantial power when active.
- Each kilowatt of strip heat consumes exactly 1 kW of electricity for every hour of operation.
- A 10 kW strip heater running for 10 hours consumes 100 kWh, adding $12 to $16 to a daily bill at typical US rates.
- Unnecessary strip heat during mild weather is the most common cause of high winter utility bills reported by heat pump owners.
Comparing Heat Pump Efficiency to Electric Resistance
A heat pump in heating mode typically operates with a coefficient of performance between 2.5 and 4.0, delivering 2.5 to 4 times as much heat energy as the electrical energy it consumes. Electric resistance heat has a COP of exactly 1.0, converting every watt of electricity into exactly one watt of heat. While electric resistance is 100 percent efficient at converting electricity to heat, a heat pump delivers roughly three times more heat for the same electrical input under most conditions.
This efficiency gap means that every minute strip heat runs when the heat pump could have done the work, the homeowner pays two to three times more. The situation worsens when strips activate in mild weather well above freezing. As noted in an analysis on ground source and air source heat pump energy efficiency, proper system sizing and control logic are essential for realizing the full benefits of heat pump technology.
| Heating Method | COP Range | Energy Input for 10,000 BTU | Relative Operating Cost |
|---|---|---|---|
| Heat pump at 40°F outdoor | 3.0 – 4.0 | 0.73 – 0.98 kWh | 1x (baseline) |
| Heat pump at 20°F outdoor | 2.0 – 2.5 | 1.17 – 1.47 kWh | 1.3x – 1.5x |
| Electric resistance strip | 1.0 | 2.93 kWh | 3x – 4x |
| Cold-climate heat pump at -10°F | 1.5 – 2.0 | 1.47 – 1.95 kWh | 1.5x – 2x |
The takeaway is simple: let the compressor run as much as possible and activate resistance heat only when absolutely necessary. Every degree of heat from strip heat costs three times as much as compressor-driven heat.
Common Control and Wiring Mistakes That Trigger Backup Heat
Several configuration issues cause strip heat to activate more often than it should, and these problems are common in both new and existing systems. One frequent mistake involves the emergency heat setting. Heat pump thermostats offer two modes: Heat mode, which uses the compressor as primary source and calls on strip heat only when needed, and Emergency Heat mode, which locks out the compressor entirely and delivers all heat through electric resistance strips.
Selecting Emergency Heat disables a working compressor even though it could still provide useful heat, making all heating come from the most expensive source. This setting is intended only for situations where the compressor has failed and requires service.
Having a qualified HVAC professional verify thermostat wiring and configuration settings delivers high returns on investment. For homeowners considering heat pump water heating, our guide to advanced water heater replacement with tankless heat pumps covers another application of the same principle.
Alternative Solutions for Supplemental and Emergency Heat
One way to avoid electric resistance auxiliary heat problems is not to use it at all. Several viable alternatives exist, each with distinct trade-offs depending on climate, home size, and existing infrastructure.
Cold-climate heat pumps maintain full capacity down to -5°F and deliver roughly 80 percent of rated capacity at -15°F. A properly sized cold-climate unit may eliminate the need for supplemental electric resistance in all but extreme weather. Even these systems still need an emergency heat plan for compressor failure.
Dual-fuel systems pair a heat pump with a gas or propane furnace. At a predetermined temperature, the system switches entirely to the furnace. Since they never run simultaneously, the furnace provides full replacement heat. This approach works well in colder climates with natural gas available. For even greater efficiency, a geothermal heat pump comprehensive residential guide explains how ground-source systems avoid the capacity loss affecting air-source units.
Hydronic coils offer another route. A hydronic coil connected to a boiler or water heater provides supplemental heat without electricity resistance. This is common in commercial buildings and is gaining traction in residential retrofits with existing boiler infrastructure.
Space heaters can be surprisingly practical for low-load homes. Some homeowners in cold climates use heat pumps with no auxiliary heat at all. When temperatures drop, a single space heater in the main living area may provide all the extra warmth needed.
Redundancy through multiple units helps in two ways. Multiple indoor units connected to separate outdoor units mean one compressor failure leaves others operational. Open floor plans may also let warm air from zones with excess capacity help heat other areas. For more on ground-source system performance, read our analysis of geothermal systems for buildings covering design, installation, and performance.
Making Practical Decisions About Auxiliary Heat
Not every home can eliminate electric resistance backup, and in many cases it remains the most practical choice. Roughly half or more of residential HVAC designs include strip heat. The decision depends on climate zone, house load, equipment selection, and homeowner comfort preferences.
Some homeowners accept undersizing their heat pump and letting indoor temperatures drift during extreme cold. Others insist on maintaining 75°F regardless of outdoor conditions. Neither approach is wrong, but each requires a different auxiliary heat strategy. The key is matching equipment capacity and controls to the real heating load, not installing strip heat as a default safety net.
- Have a Manual J load calculation performed for your home.
- Select a heat pump model with a balance point matching your climate and insulation.
- Configure thermostat staging so strip heat activates only when the compressor cannot satisfy demand.
- Set outdoor temperature lockouts to the lowest practical level, matching the heat pump balance point.
- Verify wiring annually after any thermostat replacement or HVAC service visit.
- Monitor winter electricity bills for sudden increases indicating unnecessary strip heat use.
Electric resistance heat is not inherently bad. Properly configured, strip heat provides reliable insurance against extreme weather and equipment failure without excessive operating costs.
For homeowners in colder regions, our guide on heat pump operation in cold climates covers real-world performance data and best practices.
The avoidable downside of heat pumps is not a technology flaw but a configuration problem correctable with proper design, thoughtful programming, and regular maintenance. Like Achilles, the heat pump is a capable warrior. Its weakness lies not in its own abilities but in how its support system is deployed. When electric resistance auxiliary heat is properly managed, the heat pump delivers efficient, affordable comfort year-round.