Heat pumps lose efficiency below 32°F and may stop heating altogether around 0°F
Most air-source heat pumps begin to struggle when outdoor temperatures drop below freezing (32°F). The colder it gets, the harder the unit works to pull heat from outside air, and the less heat it can actually deliver to your home. Below about 0°F, many standard heat pumps cannot heat your home on their own and will switch to a backup heating system — usually electric resistance heat or a furnace — to keep you warm.
The exact temperature at which your heat pump becomes unreliable depends on the model, the age of the unit, and whether it has a cold-climate upgrade. Newer cold-climate heat pumps can operate down to −13°F or lower, but standard models typically lose the ability to keep up somewhere between 0°F and 20°F. If you live in a region where temperatures regularly dip below freezing, this matters for both comfort and cost.
Key Takeaways
- Standard heat pumps lose heating power below 32°F and stop working as the primary heat source around 0°F.
- Cold-climate heat pumps are designed to work down to −13°F or lower and cost more upfront but reduce backup heating use.
- When a heat pump switches to backup heat, your energy bills rise sharply because electric resistance heating is expensive to run.
- The outdoor unit may ice over during defrost cycles, which is normal, but excessive frost buildup signals a problem.
- Proper maintenance — clean filters, clear coils, and annual service — helps your heat pump perform better in cold weather.
Why heat pumps struggle in cold weather
A heat pump works by moving heat from one place to another, not by generating it. In heating mode, it pulls heat from the outdoor air and moves it inside. Even cold air contains some heat energy, but as the temperature drops, there is less heat available to extract. The compressor has to work much harder to pull that heat out, and the system becomes less efficient.
Below 32°F, the outdoor coil also begins to frost over. The heat pump runs a defrost cycle to melt the ice, but during that cycle it is not heating your home — and it actually pulls heat from inside to warm the outdoor coil. This cycle repeats more often as temperatures drop, further reducing the net heat delivered to your house.
At around 0°F, most standard heat pumps reach their limit. The outdoor coil cannot extract enough heat to meet your home's heating demand, even with the compressor running at full capacity. At this point, the system switches to backup heat to avoid letting your home get cold.
Standard heat pumps versus cold-climate models
A standard air-source heat pump is designed for climates where winter temperatures rarely drop below 20°F. It has a backup heating system built in for colder days. In regions where that happens often, the backup runs frequently, and your heating bills climb.
A cold-climate heat pump uses a larger compressor, a more efficient refrigerant, and sometimes a variable-speed compressor that adjusts its output based on demand. These units can heat your home down to −13°F or even lower without switching to backup heat. They cost $1,000 to $3,000 more than a standard unit, but in a cold region they pay for themselves through lower operating costs over time.
If you live where winter temperatures regularly stay below 20°F for weeks at a time, a cold-climate model is worth the extra cost. If you live where freezing temperatures are rare and brief, a standard heat pump with a backup system is usually the right choice.
What happens when your heat pump switches to backup heat
When outdoor temperature drops below your heat pump's operating limit, a thermostat setting called the balance point triggers the backup system. This is usually electric resistance heat — essentially a large toaster element that heats air directly. Some homes use a furnace as backup instead.
Electric resistance heat is expensive to run. It uses roughly three times more electricity than a heat pump does to produce the same amount of warmth. If your backup heat runs for several weeks during a cold snap, you will see a noticeable jump in your electric bill. In some cases, homeowners in cold climates find that their winter heating costs are higher with a heat pump than they were with a furnace alone.
You cannot prevent the backup from kicking in — it is a safety feature to keep your home warm. But you can reduce how often it runs by choosing a cold-climate heat pump if you live in a cold region, or by keeping your thermostat set a degree or two lower than you might otherwise prefer.
Frost and ice buildup on the outdoor unit
During winter operation, frost and ice will form on the outdoor coil. This is normal. The heat pump runs a defrost cycle — usually every 30 to 90 minutes — to melt the ice so air can flow through the coil. You may hear the unit switch to a different sound or see steam rising from it during defrost.
Heavy ice buildup that does not melt away between defrost cycles, or ice that forms on the fan blades or frame, signals a problem. This can happen if the defrost sensor is broken, if the refrigerant charge is low, or if the coil is dirty. Call a technician if ice buildup looks excessive or if the unit is not heating your home as well as it used to.
Do not try to chip ice off the unit yourself. You can damage the coil or the refrigerant lines, which are expensive to repair. Let the defrost cycle do the work, or call a professional.
Maintenance to keep your heat pump working in cold weather
A well-maintained heat pump performs better in cold conditions than a neglected one. Change your furnace filter every month during heating season — a clogged filter reduces airflow and makes the system work harder. Check the outdoor unit after heavy snow or wind and clear away leaves, branches, or snow that blocks the coil.
Have a technician service your heat pump once a year, ideally in the fall before heating season starts. They will check the refrigerant charge, clean the coils, inspect the defrost sensor, and make sure the compressor is running smoothly. A unit that is low on refrigerant will struggle even more in cold weather and will waste energy trying to heat your home.
If you notice that your heat pump is running constantly but your home is not getting warm, or if your heating bills have jumped sharply, call a technician. These are signs that the system is working harder than it should be, often because of a maintenance issue that is straightforward to fix.
Choosing a heat pump if you live in a cold climate
If you are replacing a furnace or adding heat in a region where winter temperatures regularly drop below 20°F, ask your installer about cold-climate models. Compare the upfront cost against the expected heating bills over 10 to 15 years — the lifespan of a heat pump. In many cold regions, the fuel savings of a cold-climate heat pump outweigh the higher purchase price.
Also ask about the balance point — the temperature at which the backup heat kicks in. A good installer will set this as low as possible so the heat pump does most of the heating work. Some systems let you adjust the balance point yourself through the thermostat, which gives you control over when backup heat runs.
If you already have a standard heat pump and live in a cold climate, you cannot change how cold it can operate. But you can reduce your heating costs by keeping your thermostat a few degrees lower, making sure the unit is well-maintained, and understanding that higher winter bills are normal when backup heat runs frequently.
Frequently Asked Questions
Can I use a heat pump in a place where it gets below zero?
A standard heat pump will not heat your home below 0°F and will rely entirely on backup heat. A cold-climate heat pump can heat down to −13°F or lower. If your area regularly reaches those temperatures, a cold-climate model is necessary. If freezing weather is rare, a standard heat pump with backup is acceptable, though your heating bills will be higher during cold snaps.
Why does my heat pump ice over in winter?
Frost and ice form on the outdoor coil because the refrigerant inside is colder than the air outside. The heat pump runs a defrost cycle to melt the ice so air can flow through. This is normal operation. Heavy ice that does not melt away, or ice on the frame and fan, means the defrost system is not working and you should call a technician.
Will my heat pump heat my home if it is 10°F outside?
Most standard heat pumps will heat at 10°F, but with reduced capacity. The system will run constantly and may not keep your home as warm as you want. Below 0°F, a standard heat pump cannot heat your home on its own and will switch to backup heat. A cold-climate heat pump will continue heating down to −13°F or lower.
How much more does a cold-climate heat pump cost?
A cold-climate heat pump typically costs $1,000 to $3,000 more than a standard model, depending on the size and brand. Over 10 to 15 years, the lower operating costs in winter often make up the difference. Ask your installer for a cost comparison based on your local climate and electricity rates.
Should I turn off my heat pump in winter and use my furnace instead?
No. A heat pump is more efficient than a furnace down to its operating limit, even when backup heat is running. Switching to a furnace only makes sense if your heat pump is broken. If you are concerned about winter costs, focus on maintenance and setting your thermostat a degree or two lower instead.