Heat pumps work in cold weather, but their heating power drops as the temperature falls

A heat pump pulls heat from outside air even when it is cold, then moves that heat indoors. The colder it gets, the less heat is available to pull, so the system works harder and produces less warmth per unit of electricity. Most air-source heat pumps lose efficiency around 32°F (0°C) and become noticeably less effective below 0°F (−18°C). In very cold climates, many heat pump systems include a backup electric heater that turns on automatically when outdoor temperatures drop too far.

The key difference between a heat pump and a furnace is that a furnace burns fuel to create heat, while a heat pump moves existing heat from one place to another. This means a heat pump never stops working in cold weather—it just works less efficiently. Whether that trade-off makes sense for your home depends on your local climate, your current heating system, and how much you pay for electricity versus gas or oil.

Key Takeaways

  • Heat pumps extract heat from outdoor air even below freezing, but pull less heat as temperatures drop, requiring the system to run longer to reach your target temperature.
  • Most air-source heat pumps show a noticeable drop in efficiency around 32°F and become significantly less effective below 0°F, at which point a backup heater usually activates.
  • Cold-climate heat pumps are designed to work down to −13°F (−25°C) or lower and cost more upfront but maintain better efficiency in freezing conditions than standard models.
  • In regions where winter temperatures regularly stay above 20°F (−7°C), a standard heat pump can handle most or all heating needs without backup heat.
  • Backup electric resistance heat is less efficient than the heat pump itself but prevents your home from getting cold if the outdoor unit ices over or temperatures plummet.

Why heat pumps lose power in freezing temperatures

Heat always moves from warmer to cooler places. When outdoor air is 20°F (−7°C), there is still heat energy in that air—just less of it than when it is 50°F (10°C). A heat pump's job is to extract that heat and concentrate it indoors. The larger the temperature difference between outside and inside, the harder the heat pump has to work to move heat against its natural direction.

Think of it like pumping water uphill: the higher the hill, the more energy you need. When it is 20°F outside and you want 70°F inside, the "hill" is 50 degrees. When it is −10°F outside, the hill is 80 degrees. The system runs longer, draws more electricity, and still delivers less heat per hour than it would on a milder day. This is why the heating output rating of a heat pump always includes a temperature at which it was measured—usually 47°F (8°C).

Frost and ice buildup on the outdoor unit

When outdoor humidity is high and temperatures are near freezing, moisture in the air condenses on the outdoor unit and freezes. This frost layer blocks airflow through the coils, reducing the heat pump's ability to extract heat. Most modern heat pumps have a defrost cycle that reverses the system briefly to melt ice off the coils, but this process uses energy and temporarily stops heating your home.

If frost buildup happens frequently during your heating season, the repeated defrost cycles add up and lower your overall efficiency. Some installers recommend keeping the outdoor unit clear of snow and debris to help airflow, though the system is designed to handle some buildup. If ice forms so thickly that the defrost cycle cannot clear it, the backup heater turns on to keep your home warm while the outdoor unit recovers.

Standard heat pumps versus cold-climate models

A standard air-source heat pump is rated down to about 0°F (−18°C), meaning it will still produce heat below that temperature but with very low efficiency. Below 0°F, most standard models rely almost entirely on backup electric heat because the outdoor unit cannot extract enough heat to be worthwhile.

Cold-climate heat pumps are engineered to work efficiently down to −13°F (−25°C) or even lower. They use larger compressors, better insulation, and more efficient refrigerant cycles to extract heat in extreme cold. They cost $1,500 to $3,000 more than standard models but maintain useful heating output in temperatures where a standard heat pump would be nearly useless. If you live where winter temperatures regularly drop below 0°F, a cold-climate model can cut your reliance on backup heat by 50 percent or more.

When backup heat turns on and how much it costs

Backup electric resistance heat is a coil of wire that heats up like a toaster element. It turns on automatically when the outdoor temperature drops below a set point (usually between −5°F and 15°F, depending on your system settings) or when the heat pump cannot keep up with demand. It also activates if the outdoor unit ices over and the defrost cycle is running.

Backup heat is less efficient than the heat pump itself because it converts electricity directly to heat with no amplification. A heat pump in moderate cold can deliver 2 to 3 units of heat for every unit of electricity it uses; backup heat delivers only 1 unit of heat per unit of electricity. However, backup heat is necessary in extreme cold because the heat pump alone cannot keep your home warm fast enough. The system is designed to use backup heat sparingly—only when outdoor temperatures are very low or heating demand spikes suddenly.

If your backup heat runs constantly during winter, it usually signals a problem: the heat pump may be undersized for your home, the outdoor unit may be blocked by snow or ice, or the system settings may need adjustment. A technician can check whether the backup threshold is set too high, which would cause unnecessary electric heating.

Heat pump performance in different cold climates

How well a heat pump works in your area depends on how cold it gets and how often. In the Pacific Northwest, where winter temperatures hover around 35°F to 45°F (2°C to 7°C), a standard heat pump can handle nearly all heating with minimal backup heat. In the upper Midwest or Northeast, where temperatures drop to 0°F (−18°C) or below for weeks at a time, a standard heat pump will rely on backup heat for a significant portion of the winter.

In very cold regions like Minnesota, Wisconsin, or upstate New York, a cold-climate heat pump paired with a well-insulated home can reduce backup heat use to 10 to 20 percent of total heating. In milder cold climates like parts of Pennsylvania or Ohio, a standard heat pump might use backup heat for 20 to 40 percent of the season. The exact percentage depends on your home's insulation, air sealing, thermostat settings, and how much you heat your home.

Comparing heat pump heating to furnaces in cold weather

A gas furnace produces the same amount of heat whether it is 50°F or −20°F outside—the only difference is how often it runs. A heat pump produces less heat as temperatures drop, so it runs more often and may not keep up with extreme cold without backup heat. However, a heat pump is still more efficient than a furnace in mild winter weather, which is why many cold-climate homes use both.

If you are replacing an old furnace with a heat pump in a cold region, expect to use some backup heat on the coldest days. If you are adding a heat pump to an existing furnace, you can keep the furnace as backup and switch between them based on temperature. Some systems do this automatically; others require you to adjust your thermostat. The trade-off is that you save money on heating during the many mild winter days when the heat pump is efficient, and you accept higher costs on the few very cold days when backup heat runs.

Frequently Asked Questions

At what temperature do heat pumps stop working?

Heat pumps do not stop working until they reach their minimum operating temperature, usually around −22°F (−30°C) for standard models and −40°F (−40°C) for cold-climate models. Below that point, the refrigerant cannot circulate properly. Before that limit, the heat pump keeps running but produces very little heat, so backup electric heat takes over.

Will a heat pump keep my house warm in a blizzard?

A heat pump alone may not keep your home warm enough during extreme cold and heavy snow, especially if the outdoor unit gets buried. Most heat pump systems include backup electric heat for this reason. If your home is well-insulated and you have a cold-climate heat pump, it can handle most blizzard conditions, but backup heat will run heavily. If your home is poorly insulated, you may need to lower your thermostat or use supplemental heating.

Does snow on the heat pump outdoor unit reduce efficiency?

Yes, snow blocks airflow through the coils and reduces heating output. Most heat pump defrost cycles can melt light snow, but heavy accumulation should be cleared away. Keeping the area around the outdoor unit clear of snow and ice helps the system work more efficiently, though the system is designed to handle some buildup without damage.

Is it cheaper to heat with a heat pump or a furnace in cold weather?

In very cold weather, a furnace is usually cheaper to operate because it does not lose efficiency as temperatures drop. However, a heat pump is cheaper during mild winter days, which make up most of the heating season in many regions. Over a full winter, a heat pump often costs less than a furnace in climates where temperatures stay above 20°F (−7°C) most of the time, even accounting for backup heat use.

Can I install a heat pump if I live somewhere that gets below zero?

Yes, but you should choose a cold-climate model and may support your home is well-insulated. A standard heat pump will work but will rely heavily on backup electric heat, which is expensive. A cold-climate heat pump costs more upfront but reduces backup heat use significantly and may be the better choice if you plan to stay in the home for many years.