Heat Pump Auxiliary Electric Heat Strips Generator Sizing Guide (2026)
Auxiliary heat strips draw 5,000 to 10,000 watts per heating bank, instantly overloading portable generators. To heat on backup power, run the heat pump compressor only or lock out auxiliary strips at the thermostat.
01 Why Electric Heat Strips Overload Generators
Heat pump systems use outdoor compressors to heat efficiently in mild weather. In freezing winter storms below 25 degrees Fahrenheit, electric resistance heat strips turn on automatically.
A typical 10kW auxiliary heat strip bank draws 41.7 continuous amps at 240 volts, requiring over 10,000 watts of pure electricity for heat strips alone.
NEC 220 mandates calculating 125 percent of continuous load plus the single largest motor startup surge. Unassisted central air conditioners draw 3 to 5 times running current during startup.
- Electric resistance heat strips draw 5kW to 15kW of continuous power.
- Portable generators cannot handle heat strips plus household loads.
- Heat pump compressors consume only 2,500 to 4,000 watts when running.
02 How to Lock Out Heat Strips During Outages
Smart thermostats allow locking out auxiliary heat strips when the home switches to generator power.
Alternatively, install a manual toggle switch or trip the dedicated 60A auxiliary heat breaker in your air handler cabinet before starting generator power.
| Heating Mode | Electrical Draw | Amps @ 240V | Generator Compatibility |
|---|---|---|---|
| Heat Pump Compressor Only | 2,800 to 4,200 Watts | 12 to 18 Amps | Fits 8kW+ Generators |
| 5kW Heat Strip Bank | 5,000 Watts | 20.8 Amps | Requires 12kW+ Generator |
| 10kW Heat Strip Bank | 10,000 Watts | 41.7 Amps | Requires 22kW+ Standby |
| 15kW Heat Strip Bank | 15,000 Watts | 62.5 Amps | Requires 30kW+ Commercial |
NEC 220 mandates calculating 125 percent of continuous load plus the single largest motor startup surge. Unassisted central air conditioners draw 3 to 5 times running current during startup.
- Shut off the 60A heat strip breaker to let the heat pump compressor run.
- Pair the outdoor heat pump compressor with an A/C soft-starter.
- Use wood stoves or portable propane heaters as auxiliary winter backup.
Frequently Asked Questions
Q: Can my heat pump provide heat without auxiliary heat strips?
Yes. Modern cold-climate heat pumps continue extracting heat from outdoor air down to minus five degrees Fahrenheit without engaging auxiliary electric strips.
Q: Will my generator trip if Emergency Heat is engaged?
Yes. Switching your thermostat to Emergency Heat forces resistance strips ON, immediately exceeding the 50-amp capacity of portable home generators.