Heat pumps lose efficiency below 32°F and may stop heating altogether below 0°F

A heat pump pulls warmth from outside air and moves it indoors. As outdoor temperature drops, there is less warmth to extract, so the system works harder and produces less heat. Most air-source heat pumps — the most common type — begin to lose noticeable heating power around 32°F (0°C). Below that point, efficiency drops steadily. When the temperature reaches 0°F (-18°C) or lower, many heat pumps cannot keep a home warm on their own and will not operate at all without a backup heating source.

The exact temperature at which your heat pump stops working depends on the model, the outdoor unit's design, and whether it has a backup system. Some newer cold-climate heat pumps are engineered to work down to -13°F (-25°C) or lower, but standard models typically cannot. If you live where winter temperatures regularly drop below freezing, you need to know your system's limits before the cold arrives.

Key Takeaways

  • Standard air-source heat pumps lose heating power below 32°F and stop working entirely around 0°F, though cold-climate models perform better.
  • When a heat pump cannot heat your home, a backup system — usually electric resistance heat or a gas furnace — takes over automatically.
  • You can check your heat pump's cold-weather performance by finding the manufacturer's specifications for your exact model and outdoor unit.
  • Keeping your outdoor unit clear of snow and ice, and scheduling maintenance before winter, helps your heat pump work as well as possible in cold weather.

Why heat pumps struggle in freezing temperatures

Heat pumps work by circulating refrigerant through an outdoor coil that absorbs heat from the air, then moving that heat indoors. The colder the outside air, the harder the refrigerant has to work to extract that heat. At 32°F, the outdoor air holds significantly less thermal energy than at 50°F. By the time outdoor temperature reaches 0°F, the amount of usable heat in the air drops so much that the compressor — the pump's engine — cannot pull enough warmth to meet your home's heating demand.

Additionally, when outdoor temperature drops below about 40°F, frost and ice begin to form on the outdoor coil. This buildup blocks airflow and reduces the coil's ability to absorb heat. The system must periodically reverse direction to defrost the coil, which temporarily stops heating your home and sends warm air outdoors. In very cold weather, the heat pump spends so much time defrosting that it cannot keep up with your heating needs.

How backup heating systems keep your home warm

Nearly all heat pump installations include a backup heating source — usually electric resistance heat (similar to a space heater) or a gas furnace. When outdoor temperature drops below your heat pump's operating limit, or when the system cannot produce enough heat to warm your home, the backup automatically switches on. You typically do not notice this change; the thermostat straightforward calls for backup heat without your input.

Electric resistance heat is the most common backup because it integrates easily with a heat pump system. It is less efficient than the heat pump itself — it converts electricity directly to heat rather than moving existing heat — so your energy bills will rise when the backup is running. If your system uses a gas furnace as backup, the furnace takes over when the heat pump cannot keep up, and you will see higher gas usage during cold spells.

Some heat pump systems have a setting called auxiliary heat or emergency heat that you can manually switch on. Avoid using this mode unless the heat pump has failed entirely, because it bypasses the heat pump and uses only the backup system, which costs more to run.

Cold-climate heat pumps and their temperature limits

Manufacturers now produce heat pumps specifically designed for cold regions. These models use larger compressors, improved refrigerants, and better outdoor coil designs to extract heat even when outdoor temperature is very low. Cold-climate heat pumps typically maintain reasonable heating output down to -13°F (-25°C) or even lower, depending on the brand and model.

If you live in a region where winter temperatures regularly drop below 0°F, a cold-climate heat pump may reduce your reliance on backup heating and lower your winter energy costs. However, these units cost more upfront than standard models. To determine whether the investment makes sense for your location, compare the price difference against the heating cost savings over the system's lifespan — usually 15 to 20 years.

Check the manufacturer's specifications for any heat pump you are considering. Look for the heating capacity at specific outdoor temperatures (usually listed at 47°F, 32°F, and 0°F). This tells you how much heat the unit can produce at each temperature and helps you understand when backup heating will set up.

Maintaining your heat pump for winter performance

A well-maintained heat pump performs better in cold weather than a neglected one. Before winter arrives, have a technician inspect the outdoor unit, check refrigerant levels, and clean the coil. A dirty coil reduces heat transfer and makes frost buildup worse, so the system will struggle earlier in the season and defrost more often.

During winter, keep the outdoor unit clear of snow and ice. Remove snow that piles against the unit, and do not block the intake vents. If ice forms on the coil, let the system's defrost cycle handle it — do not chip away at ice yourself, as you can damage the fins. If ice buildup is severe and the system is not defrosting properly, call a technician.

Check your thermostat settings before cold weather arrives. Make sure the system is set to heat mode, not cool mode or auto mode. In auto mode, the system may switch between heating and cooling as outdoor temperature fluctuates, which wastes energy and can confuse the backup system.

What to do if your heat pump stops working in winter

If your heat pump stops producing heat when outdoor temperature is very cold, the backup system should set up automatically. Check your thermostat to confirm it is set to heat mode and that the temperature setting is higher than the current room temperature. If the backup is running but your home is not warming, the problem may be with the backup system itself, not the heat pump.

If the outdoor unit is covered in ice or snow, clear it away and wait a few minutes to see if the system resumes heating. If the unit is clear and the backup is running but your home is still cold, turn off the heat pump and run the backup system alone. Then contact a technician — the heat pump may have a refrigerant leak, a faulty compressor, or a control problem that requires professional repair.

Do not attempt to force the heat pump to run in extremely cold weather by adjusting the thermostat or settings. If the system has shut down, it is because outdoor temperature is below its safe operating range. Running it anyway can damage the compressor and lead to expensive repairs.

Choosing between heat pump and furnace in very cold climates

If you live in a region where winter temperatures regularly drop below -10°F and stay there for weeks, a heat pump alone may not be practical, even a cold-climate model. In these areas, a traditional gas furnace or a heat pump paired with a gas furnace backup may be more reliable and cost-effective. A furnace produces full heating output regardless of outdoor temperature and does not require defrosting.

However, heat pumps are becoming more viable in cold climates as technology improves. If you are building a new home or replacing an old system, research cold-climate heat pumps for your region. Many utility companies offer rebates for cold-climate heat pump installation, which can offset the higher upfront cost. Compare the total cost of ownership — purchase price plus estimated heating bills over 15 to 20 years — rather than looking at purchase price alone.

Frequently Asked Questions

At what temperature does a heat pump stop working?

Most standard air-source heat pumps stop heating effectively around 0°F (-18°C) and cannot operate at all below that point. Cold-climate models can work down to -13°F (-25°C) or lower. Your system's exact limit depends on the manufacturer and model, so check the specifications for your unit.

Will my backup heat turn on automatically when it gets too cold?

Yes. The thermostat monitors outdoor temperature and automatically switches to backup heating when the heat pump cannot meet your home's heating demand. You do not need to manually switch systems. Avoid using the auxiliary or emergency heat setting unless the heat pump has failed.

Why is my heating bill so high in winter?

When outdoor temperature drops below your heat pump's efficient range, the backup heating system runs more often. Electric resistance backup is less efficient than the heat pump, so your energy costs rise. This is normal. If bills are unusually high, have a technician check the heat pump and backup system for leaks or faults.

Can I use my heat pump in winter if I live somewhere very cold?

Yes, but you will need a backup heating system. A standard heat pump paired with electric or gas backup works in most climates. If you want to minimize backup heating use and lower winter bills, consider a cold-climate heat pump, which maintains better efficiency at very low temperatures.

What should I do if my heat pump is frozen over?

Let the system's defrost cycle handle it. The heat pump reverses automatically to melt ice on the outdoor coil. If ice buildup is severe and the system is not defrosting properly, or if the outdoor unit is buried in snow, clear away the snow and call a technician. Do not chip at ice yourself.