Heat pumps work in cold weather, but they need help below freezing
A heat pump can heat your home even when the outdoor temperature drops below freezing, but its efficiency drops sharply as it gets colder. Most air-source heat pumps lose about half their heating power by the time outdoor temperatures reach 0°F. Below that, many models switch to electric resistance heating — essentially a backup heater that costs more to run. The colder the weather, the harder your heat pump has to work, and the higher your heating bills climb.
The key to using a heat pump in cold weather is understanding when it will and won't work well, knowing what to expect from your electric bill, and recognizing when your system needs maintenance or a backup heat source. Cold-weather performance depends on your specific model, your local climate, and how you operate the system.
Key Takeaways
- Heat pumps lose efficiency in cold weather and may automatically switch to electric resistance heating below 20°F to 30°F, which costs significantly more to operate.
- Keeping your outdoor unit clear of snow, ice, and debris helps the system pull heat from the air and prevents it from working harder than necessary.
- Setting your thermostat to heat mode and leaving it there during winter prevents the system from switching between heating and cooling, which wastes energy.
- Newer cold-climate heat pumps are designed to work efficiently down to 0°F or lower, while older models may struggle below 20°F.
- A backup heating source — whether a furnace, baseboard heater, or the system's built-in electric resistance — becomes necessary in regions with extended freezing temperatures.
Why heat pump efficiency drops in freezing temperatures
A heat pump works by moving heat from outside air into your home. Even cold air contains heat energy, and the refrigerant inside the pump can extract it. But as outdoor temperatures fall, there is less heat available to extract, so the system has to work much harder and longer to warm your home to the temperature you set.
Most air-source heat pumps reach a point called the balance point — usually between 20°F and 35°F, depending on the model — where the heat it can pull from the air no longer covers your home's heating needs. Below that point, the system automatically switches on electric resistance heating, which is essentially a large electric heater built into the system. Resistance heating delivers warmth when ready but uses far more electricity than the heat pump itself, so your heating costs jump noticeably.
If your heat pump was installed before 2015, its balance point is likely around 30°F to 35°F. Newer cold-climate models can operate efficiently down to 0°F or even lower, but they still lose performance as temperatures drop. Check your system's manual or ask your installer what temperature your specific model is rated for.
Keep the outdoor unit clear of snow and ice
The outdoor unit of your heat pump is where the actual heat exchange happens. Snow, ice, and frost buildup block airflow and force the system to work harder. In cold weather, frost forms on the coils naturally, and your system has a defrost cycle that periodically reverses to melt it off. But heavy snow or ice from storms can overwhelm that process.
After a snowstorm, clear snow away from the outdoor unit — aim for at least two feet of clearance on all sides. Do not use a pressure washer, which can damage the fins. A soft brush or your hands work fine. If ice has built up on the coils, let the defrost cycle run; do not chip away at it with tools. If frost or ice does not clear after the system runs for 15 to 20 minutes, contact a technician.
Keep leaves, twigs, and other debris away from the unit year-round. In winter, make sure snow from your roof does not slide onto the outdoor unit. If your unit sits in a spot where snow naturally drifts, consider installing a snow shield — a straightforward frame that keeps snow away without blocking airflow.
Set your thermostat to heat mode and leave it there
During winter, set your thermostat to heat mode and do not switch it to cool or auto mode, even on a warm winter day. When the thermostat is set to auto, the system can switch between heating and cooling based on small temperature swings. Each switch costs energy and can trigger the electric resistance heating unnecessarily.
If you want to cool your home on a warm day in winter, turn the system off and open a window instead. The energy cost of switching modes and running resistance heating will far exceed what you save by cooling for an hour or two.
Set your thermostat to a steady temperature and resist the urge to raise it significantly when it is very cold outside. Every degree you raise the setpoint increases your heating costs, especially when the system is relying on resistance heating. A difference of 3°F to 5°F can add 10% to 15% to your heating bill in cold weather.
Understand when your system switches to backup heating
Most heat pumps have a built-in electric resistance heater that turns on automatically when outdoor temperatures drop below the balance point. You may not notice this happening — the system straightforward delivers warm air, and you do not see which component is producing it. But your electric meter will show the difference.
Some systems also have a manual switch on the thermostat labeled "emergency heat" or "auxiliary heat." Do not use this unless the heat pump itself has failed. Resistance heating costs roughly two to three times more per unit of heat than the heat pump, so running it manually will spike your bill.
If you live in a region where temperatures regularly drop below your system's balance point for weeks at a time, talk to your installer about whether a backup furnace or other heat source makes financial sense. In some climates, a hybrid system — heat pump plus furnace — costs less to operate over a winter than a heat pump alone.
Schedule maintenance before winter arrives
Have your heat pump serviced in the fall, before cold weather begins. A technician will check the refrigerant charge, clean the coils, inspect the defrost cycle, and make sure the electric resistance heating is working properly. A system running low on refrigerant will struggle even more in cold weather.
Ask the technician to confirm your system's balance point and heating capacity at your local winter temperatures. If your system is more than 10 years old and you live where winters are harsh, ask whether upgrading to a cold-climate model would lower your heating costs. Newer units are significantly more efficient in freezing temperatures.
Check your air filter monthly during the heating season. A clogged filter forces the system to work harder and can reduce heating output by 10% to 15%. Replace it when it looks dirty — do not wait until it is completely blocked.
Know the signs your heat pump needs repair
If your heat pump is running but your home is not warming up, the system may have lost refrigerant, the defrost cycle may be stuck, or the electric resistance heating may have failed. Do not ignore this — call a technician. Running the system in this state will waste electricity without heating your home.
If you hear unusual noises from the outdoor unit during the defrost cycle — a hissing or gurgling sound — that is normal. The system is reversing the refrigerant flow to melt frost. But if you hear grinding, squealing, or banging, shut the system off and call for service.
If your heating bills are much higher than last winter even though you have not changed your thermostat settings, the system may be relying too heavily on resistance heating. This can mean the heat pump is not working properly, or it may straightforward mean your winter was colder. Check with neighbors to see if their bills also went up.
Frequently Asked Questions
Will my heat pump work at all when it is below zero?
Yes, but with very low efficiency. Most standard heat pumps will still produce heat at 0°F, but the system will rely almost entirely on electric resistance heating, which is expensive. Cold-climate heat pumps rated for sub-zero operation will continue to pull heat from the air even at 0°F or below, though at reduced capacity. Check your manual or ask your installer what your specific model is rated for.
Should I turn off my heat pump in winter and use a furnace instead?
Not unless the heat pump has failed. Even in cold weather, a heat pump is usually more efficient than electric resistance heating. If you have a furnace as a backup, the system will automatically switch to it when needed. If you have only a heat pump, the built-in resistance heating will take over below the balance point.
Why is my electric bill so high in winter if I have a heat pump?
Cold weather forces your heat pump to work longer and harder to reach your setpoint temperature. Below the balance point, the system switches to electric resistance heating, which is expensive. The colder your winter and the lower you set your thermostat, the higher your bill will be. This is normal, though a well-maintained system should not show a sudden spike compared to previous winters.
Can I use a space heater with my heat pump to save money?
No. A space heater uses as much or more electricity per unit of heat as electric resistance heating in your heat pump. The only way to save money is to lower your thermostat setpoint or improve your home's insulation so the heat pump does not have to work as hard.
How often should I have my heat pump serviced in winter?
One service visit in the fall is standard. If you notice problems during winter — reduced heating, unusual noises, or a sudden spike in your bill — call for service then. Do not wait until spring. A failing component in winter will cost you money every day it is not fixed.