Heat pumps do work below freezing, but their heating power drops as the temperature falls

A heat pump extracts heat from outside air even when it is below 32°F (0°C), but the amount of heat it can pull decreases the colder it gets. At 32°F, most air-source heat pumps still deliver useful heating. By the time outdoor temperature reaches 0°F (−18°C), many standard models produce only 50 to 70 percent of their rated capacity. Below zero, some heat pumps struggle enough that a backup heating system kicks in automatically.

The reason is physics: there is still thermal energy in cold air—heat always exists unless you reach absolute zero (−459°F). A heat pump's refrigerant can still absorb that energy and move it indoors. But as outdoor air gets colder, the temperature difference between the air and the refrigerant shrinks, making the transfer slower and less efficient. Your system works harder to pull the same amount of heat.

Whether your heat pump remains your primary heater below freezing depends on the model, your climate, and whether you have a backup system installed. Most homes in cold climates pair a heat pump with electric resistance heat or a furnace that activates when outdoor temperatures drop below a set point—often around 35°F to 40°F.

Key Takeaways

  • Heat pumps extract heat from outdoor air even at freezing temperatures, but their heating output declines as it gets colder.
  • At 0°F, a standard air-source heat pump typically produces 50 to 70 percent of its rated heating capacity.
  • Homes in climates with sustained freezing temperatures usually pair a heat pump with a backup heating source that activates automatically.
  • Cold-climate heat pumps are designed to work efficiently down to around −13°F (−25°C) and may cost more upfront but reduce reliance on backup heat.
  • Defrost cycles—when the system reverses to melt frost buildup on the outdoor unit—reduce heating output for 5 to 15 minutes several times per day in freezing weather.

Why heating capacity drops below 32°F

Heat pump efficiency is measured by a number called COP (coefficient of performance), which compares the heat output to the electrical energy used. At 47°F outdoor temperature, a typical air-source heat pump might have a COP of 3, meaning it produces three units of heat for every one unit of electricity. At 32°F, that same unit might drop to a COP of 2.5. At 0°F, it could fall to 1.5 or lower.

This happens because the refrigerant inside the heat pump must be colder than the outdoor air to absorb heat from it. In freezing conditions, the refrigerant has to work much harder—and use more electricity—to reach the temperature difference needed for heat transfer. The system is still moving heat indoors, but it is moving less of it per hour, and your electric bill reflects the extra work.

Additionally, frost and ice accumulate on the outdoor unit's coil when humidity freezes on contact. This buildup acts as insulation, blocking heat transfer. The system must periodically reverse itself into cooling mode (called a defrost cycle) to melt the ice off. During these cycles—which last 5 to 15 minutes and may occur several times per day—your heat pump stops heating and may even blow cool air indoors while it clears the coil.

Standard heat pumps versus cold-climate models

A standard air-source heat pump is rated for operation down to around 0°F, though it becomes increasingly inefficient below 35°F. Manufacturers design these units for moderate climates where freezing temperatures are occasional rather than sustained.

Cold-climate heat pumps are engineered to work efficiently down to −13°F (−25°C) or even lower. They use larger compressors, more refrigerant, and improved heat exchangers to extract heat more effectively from very cold air. Some models include variable-speed compressors that adjust their speed based on outdoor temperature, reducing energy waste. Cold-climate models cost 20 to 40 percent more than standard units but significantly reduce the hours your backup heating system runs.

If you live in a region where winter temperatures regularly drop below 20°F, a cold-climate heat pump is worth the upfront cost because it will heat your home more efficiently and reduce your reliance on expensive backup heat. If freezing temperatures are rare or brief, a standard heat pump paired with a backup system is usually the more economical choice.

How backup heating systems work with heat pumps

Most heat pump installations in cold climates include a backup heating source that activates automatically when outdoor temperature drops below a set threshold. This threshold—called the balance point—is typically set between 35°F and 40°F, though it can be adjusted based on your system and preferences.

When outdoor temperature falls below the balance point, your thermostat signals the backup system to turn on. The backup is usually electric resistance heat (similar to a space heater), a gas furnace, or an oil boiler. The heat pump continues running alongside the backup, but the backup handles most of the heating load because it is more efficient than a struggling heat pump in extreme cold.

You do not have to manually switch between systems—the thermostat manages it automatically. However, you can adjust the balance point if you want the heat pump to run longer (using more electricity but less backup heat) or shorter (using less electricity but more backup heat). Most homeowners leave it at the factory setting unless they notice their electric bills spiking during winter.

Defrost cycles and their effect on comfort

When frost builds up on the outdoor coil, the heat pump reverses its operation temporarily to heat the outdoor unit instead of your home. This melts the ice so heat transfer can resume. A defrost cycle typically lasts 5 to 15 minutes and may occur every 30 to 90 minutes during freezing weather, depending on humidity and temperature.

During a defrost cycle, indoor heating stops and the outdoor fan shuts off. If your backup heat is not running, you may notice the indoor temperature drop slightly—usually 1 to 3 degrees—before the cycle ends and normal heating resumes. Some systems include a defrost information feature that turns on backup heat during the cycle to maintain indoor temperature, but this increases energy use.

Modern heat pumps use smart defrost controls that monitor frost buildup and only trigger a cycle when necessary, rather than on a fixed schedule. This reduces the number of interruptions and saves energy. If you find defrost cycles uncomfortable, ask your installer whether your system has this feature or whether it can be enabled.

Real-world performance in freezing climates

A homeowner in Minneapolis with a standard heat pump and a gas furnace backup might see the heat pump handle 70 to 80 percent of winter heating when temperatures stay above 20°F. Once temperatures drop below 0°F and stay there for days, the furnace takes over and the heat pump runs minimally. Over a full winter, the heat pump still provides 40 to 60 percent of total heating in cold climates, with the backup furnace covering the rest.

In milder cold climates—such as parts of Pennsylvania, Ohio, or upstate New York where winter temperatures rarely drop below 10°F—a standard heat pump with backup heat can handle 60 to 75 percent of annual heating. The backup system runs less frequently and for shorter periods, keeping overall heating costs lower than an all-furnace system would.

In very cold climates like Minnesota, Wisconsin, or Maine, a cold-climate heat pump paired with backup heat can reduce furnace runtime by 30 to 50 percent compared to a standard heat pump, translating to measurable savings on heating bills despite the higher initial cost of the cold-climate unit.

Maintenance and winterization for freezing weather

Heat pumps in cold climates need specific maintenance to perform reliably below freezing. Before winter, have a technician check refrigerant charge, inspect the outdoor coil for damage, and verify that defrost controls are working correctly. A low refrigerant charge makes the system even less efficient in cold weather and can damage the compressor.

Keep the outdoor unit clear of snow and ice buildup. While the defrost cycle handles frost on the coil itself, heavy snow or ice around the unit blocks airflow and forces the system to work harder. Clear a 2-foot radius around the outdoor unit after snowstorms. Do not cover the unit with a tarp or box—this traps moisture and prevents proper operation.

Check your backup heating system as well. If you have a furnace, change the filter before winter and have it serviced. If you have electric resistance heat, make sure the thermostat is set correctly so it activates at your chosen balance point. A malfunctioning backup system means your heat pump alone must handle extreme cold, which it cannot do efficiently.

Frequently Asked Questions

Will my heat pump stop working if it gets too cold?

No. A heat pump will continue operating at temperatures well below freezing, but its heating output drops significantly. Most units are designed to work down to 0°F, though efficiency is poor. Below 0°F, many standard heat pumps produce so little heat that a backup system becomes the primary heater. Cold-climate models are rated to work efficiently down to −13°F or colder.

Why does my heat pump blow cold air in winter?

During a defrost cycle, the heat pump reverses to melt frost off the outdoor coil. This temporarily stops indoor heating and may blow cool air for 5 to 15 minutes. This is normal. If cold air blows continuously, your backup heat may not be activating, or the system may have a refrigerant leak—call a technician.

Is it cheaper to run a heat pump or a furnace in freezing weather?

Below about 35°F, a furnace is usually more efficient than a heat pump because the heat pump must work so hard to extract heat from cold air. That is why most cold-climate installations pair a heat pump with a furnace backup. The heat pump runs when it is efficient (above 35°F), and the furnace takes over when it is not.

Do I need a cold-climate heat pump if I have a furnace backup?

Not necessarily. A standard heat pump with furnace backup works fine in most climates and costs less upfront. A cold-climate heat pump makes sense if you want to minimize furnace runtime, reduce heating bills, or live in a region where temperatures regularly drop below 10°F for extended periods.

How often do defrost cycles happen in freezing weather?

Defrost cycles typically occur every 30 to 90 minutes during freezing weather, depending on humidity and outdoor temperature. High humidity causes frost to build up faster, triggering more frequent cycles. Modern systems with smart defrost controls minimize unnecessary cycles by monitoring actual frost buildup rather than running on a fixed schedule.