Heat pumps work in cold weather, but their efficiency drops as outdoor temperature falls

A heat pump extracts heat from outside air even when it is cold, then moves that heat indoors. The process works down to around 0°F (−18°C) in most models, though the amount of heat it can pull from the air decreases sharply as temperature drops. Below freezing, a heat pump will still heat your home, but it will run longer and use more electricity to reach the same indoor temperature it would at 40°F.

The real limit is not whether a heat pump works in cold weather—it does—but whether it works well enough for your climate and your heating needs. A heat pump in Minnesota performs differently than one in North Carolina, and a model rated for −13°F operation is not the same as one rated for 0°F. Understanding these differences helps you decide whether a heat pump alone can heat your home or whether you need a backup system.

Key Takeaways

  • Most air-source heat pumps continue to heat homes in temperatures down to 0°F, but output drops by 30 to 50 percent compared to operation at 40°F.
  • Cold-climate heat pumps are engineered to work efficiently at −13°F or lower and cost more upfront but recover that cost through better winter performance.
  • Below the heat pump's rated minimum temperature, a backup heating system (electric resistance, gas furnace, or boiler) takes over to maintain indoor warmth.
  • A heat pump's winter efficiency depends on your local climate, the model's specifications, and whether it has a variable-speed compressor.
  • Defrost cycles—when the system reverses to melt ice buildup on the outdoor coil—reduce heating output on cold, humid days.

Why heat pump output drops in freezing temperatures

A heat pump works by circulating refrigerant through an outdoor coil to absorb heat from the air, then moving that heat indoors. The colder the outside air, the smaller the temperature difference between the air and the refrigerant, and the less heat the refrigerant can absorb. At 40°F outside, a typical heat pump might deliver 100 percent of its rated capacity. At 20°F, that same unit may deliver only 50 to 70 percent. At 0°F, output often falls to 30 to 50 percent of rated capacity.

This is not a failure—it is how the physics of heat transfer works. The heat pump is still pulling heat from outside, but there is less heat available to pull. To compensate, the compressor runs longer and works harder, which increases electricity use. In very cold weather, this can make the heat pump less efficient than a gas furnace, which generates heat by burning fuel rather than moving it from one place to another.

Standard heat pumps versus cold-climate models

A standard air-source heat pump is rated to operate down to about 0°F (−18°C). Below that temperature, the outdoor coil can ice over faster than the defrost cycle can clear it, and the compressor may not be able to move refrigerant efficiently. Most standard models are designed for climates where winter temperatures rarely drop below −10°F for extended periods.

A cold-climate heat pump is built to work efficiently at −13°F (−25°C) or lower. These models use a variable-speed compressor, larger outdoor coils, and improved refrigerant circulation to maintain heating output in deep cold. They also have more aggressive defrost cycles to handle frequent icing. Cold-climate models cost $1,000 to $3,000 more than standard units but are necessary if you live in a region where winter temperatures regularly drop below 0°F.

Brands like Mitsubishi, Daikin, and Fujitsu make cold-climate models rated for −13°F or lower. Standard models from most manufacturers are rated for 0°F. Check the specifications before purchase if you live in a cold region—the difference in winter performance is substantial.

Defrost cycles reduce heating output on cold, humid days

When outdoor temperature is near freezing and humidity is high, frost and ice build up on the outdoor coil. A heat pump detects this buildup and enters defrost mode: it reverses the refrigerant flow so the outdoor coil becomes warm and melts the ice. During defrost, no heat is delivered indoors—the system is using its heating capacity to clear the coil instead.

Defrost cycles typically last 5 to 15 minutes and occur every 30 to 90 minutes in icy conditions. On a day when the outdoor temperature is 30°F and humidity is high, a heat pump may spend 20 to 30 percent of its runtime in defrost mode, which cuts effective heating output by that amount. This is why heat pumps often underperform on cold, damp days compared to cold, dry days at the same temperature.

When a backup heating system becomes necessary

Most heat pump installations include a backup heating system that activates when outdoor temperature drops below the heat pump's rated minimum or when the heat pump cannot keep up with demand. Common backup systems are electric resistance heating (built into the indoor unit), a gas furnace, or a boiler. The backup system takes over automatically when needed, so you do not lose heat.

In a standard heat pump system in a cold climate, the backup may run 20 to 40 percent of winter heating hours. In a cold-climate heat pump system, backup runtime is much lower—often 5 to 15 percent—because the heat pump remains efficient at lower temperatures. The type and size of your backup system affects your total winter heating cost, so this choice matters when you install a heat pump.

Some heat pump systems use a hybrid approach: the heat pump runs whenever outdoor temperature is above its minimum, and the backup system runs when it is colder. This setup is more efficient than running the backup alone but less efficient than a heat pump in mild weather. If your area has frequent temperature swings between 0°F and 40°F, a hybrid system may cost less to operate than a heat pump alone.

How to estimate winter performance for your location

Your heat pump's winter performance depends on your local climate, not just the outdoor temperature on the coldest day. A metric called heating degree days (HDD) measures how many days per winter fall below 65°F and by how much. A location with 7,000 HDD per year (like Minneapolis) has much longer and colder winters than a location with 3,000 HDD (like Charlotte). A heat pump that works well in Charlotte may not be sufficient alone in Minneapolis.

When you get a heat pump quote, ask the installer for a heating load calculation specific to your home and your local climate. This calculation shows how much heat your home needs on the coldest day of the year and how much of that heat the heat pump can provide. If the heat pump can provide 80 to 100 percent of peak heating demand, you may not need a backup system. If it can provide only 60 to 70 percent, a backup system is necessary.

You can also check your local HDD and average winter temperatures on the National Weather Service website or through your utility company. Compare these numbers to the heat pump's rated capacity at your area's typical winter temperature. This gives you a rough sense of whether the model will work well in your climate before you commit to installation.

Maintenance and performance in winter

A heat pump in cold weather needs regular maintenance to perform well. The outdoor coil should be clear of snow and ice buildup—if snow piles up around the unit, airflow is blocked and heating output drops further. After heavy snow, brush away accumulation around the outdoor unit. Do not use a pressure washer or sharp tools, which can damage the coil.

The refrigerant charge and airflow through both indoor and outdoor coils affect winter performance. If the system is undercharged or the coils are dirty, heating output drops more in cold weather than in mild weather. Have the system serviced annually, ideally in fall before winter heating season begins. A technician can check refrigerant levels, clean coils, and verify that the defrost cycle is working correctly.

Frequently Asked Questions

Will a heat pump heat my home if it is 0°F outside?

Yes, a standard heat pump will heat your home at 0°F, but it will deliver only 30 to 50 percent of its rated heating capacity and will run much longer to reach your set temperature. A cold-climate heat pump rated for −13°F will deliver 60 to 80 percent of capacity at 0°F. If outdoor temperature drops below the heat pump's rated minimum, a backup heating system takes over.

Is a heat pump worth installing if I live somewhere that gets very cold winters?

It depends on how cold and how long. If winter temperatures regularly drop below −10°F for weeks at a time, a standard heat pump may not be cost-effective because the backup system will run most of the winter. A cold-climate heat pump is worth considering if you want to reduce reliance on gas or electric resistance heating. Compare the upfront cost of a cold-climate model to the fuel savings over 10 to 15 years.

What is a defrost cycle and why does it reduce heating?

A defrost cycle reverses the heat pump to warm the outdoor coil and melt ice buildup. During this cycle, no heat is delivered indoors. On cold, humid days, defrost cycles may run every 30 to 90 minutes for 5 to 15 minutes each, which can reduce effective heating output by 20 to 30 percent on those days.

Do I need a backup heating system with a heat pump?

Most heat pump installations include a backup system (electric resistance, gas furnace, or boiler) that activates when outdoor temperature drops below the heat pump's rated minimum or when heating demand exceeds the heat pump's output. The backup ensures your home stays warm even in extreme cold. Ask your installer whether a backup is necessary for your climate and home size.

How do I know if a heat pump will work in my climate?

Ask your installer for a heating load calculation specific to your home and local climate. This shows how much heat your home needs on the coldest day and how much the heat pump can provide. Compare the heat pump's rated capacity at your area's typical winter temperature to your home's heating needs. If the heat pump can meet 80 percent or more of peak demand, it should work well in your climate.