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

A heat pump's heating output declines in cold weather because there is less heat energy available in the outside air to extract. At 47°F, a typical air-source heat pump operates at roughly 100% of its rated capacity. At 32°F, that same unit typically delivers 70% to 80% of its rated output. Below 0°F, many standard models fall to 40% to 50% of rated capacity. The colder the air, the harder the compressor works to pull heat from it, and the less efficient the system becomes.

This does not mean a heat pump stops working in winter. It means the system must run longer and more often to reach your target temperature, which increases electricity use. In regions where winter temperatures regularly drop below 20°F, a heat pump alone may not meet peak heating demand on the coldest days. Most cold-climate installations pair a heat pump with a backup heating source—usually electric resistance heat or a gas furnace—to handle those extreme periods.

Key Takeaways

  • Heat pump efficiency declines as outdoor temperature drops, losing roughly 20% to 30% of output at 32°F compared to 47°F.
  • Below 0°F, many standard air-source heat pumps deliver only 40% to 50% of their rated heating capacity.
  • Cold-climate heat pumps with larger compressors and improved refrigerant formulas maintain better efficiency than standard models in freezing conditions.
  • Pairing a heat pump with a backup heating system is common in regions where winter temperatures regularly fall below 20°F.
  • Ground-source heat pumps maintain steadier efficiency in cold weather because they draw heat from underground, where temperature stays around 50°F year-round.

Why cold air reduces heat pump efficiency

A heat pump moves heat from outside to inside by using a refrigerant that absorbs heat at low temperatures and releases it at higher temperatures. The warmer the outside air, the easier this process is. When outdoor air is 47°F, the refrigerant can absorb heat readily and the compressor does not have to work hard. When outdoor air drops to 32°F or below, the temperature difference between the refrigerant and the outside air shrinks, so the refrigerant absorbs heat more slowly. The compressor must run longer and cycle more frequently to extract the same amount of heat.

This is thermodynamics, not a design flaw. No heat pump can overcome the basic physics that makes it harder to extract heat from cold air than from warm air. The system is still more efficient than electric resistance heating (which converts electricity directly to heat with no extraction process), but it is less efficient than it is during shoulder seasons when outdoor temperatures are moderate.

Cold-climate heat pump models and their advantages

Manufacturers now produce cold-climate heat pumps specifically designed to maintain output in freezing conditions. These models use larger compressors, improved refrigerant formulas (often R-32 or R-290), and enhanced heat exchangers to extract heat more effectively from cold air. A cold-climate model might deliver 60% to 70% of rated capacity at 0°F, compared to 40% to 50% for a standard model at the same temperature.

Cold-climate heat pumps cost more upfront—typically 15% to 25% more than standard units—but the higher efficiency in winter can reduce heating costs in cold regions. Brands including Mitsubishi, Daikin, Fujitsu, and Lennox offer cold-climate lines. If you live where winter temperatures regularly drop below 10°F, a cold-climate model is worth comparing against a standard unit paired with backup heat, because the operating costs may be similar or lower over the heating season.

Ground-source heat pumps as a cold-weather alternative

A ground-source heat pump (also called a geothermal heat pump) draws heat from the ground rather than the air. Ground temperature stays around 50°F year-round at depths of 6 to 10 feet, regardless of outdoor air temperature. This means a ground-source heat pump maintains consistent efficiency throughout winter, with no sharp drop-off as air temperature falls.

Ground-source systems are the most efficient heat pump option in cold climates, but they require excavation to install underground loops, which costs significantly more than an air-source installation—often $15,000 to $30,000 or more depending on soil conditions and loop length. They are practical for new construction or major renovation, less so for retrofitting an existing home. For homeowners in very cold regions with the budget and space for installation, ground-source heat pumps eliminate the need for backup heating and deliver the highest seasonal efficiency.

Backup heating and when it activates

Most air-source heat pump systems include a backup heating source that activates automatically when the outdoor temperature drops below a set point—often between 20°F and 35°F, depending on the system and the heating demand. The backup might be electric resistance coils built into the indoor unit, or a separate gas furnace. When backup heat runs, the system switches from heat pump mode to direct heating, which uses more energy per unit of warmth produced.

You cannot avoid backup heat set up in very cold climates; it is a necessary part of meeting peak heating load. What you can control is the backup set up temperature. Setting it lower (say, 15°F instead of 35°F) means the heat pump runs longer in cold conditions, using more electricity but less backup fuel. Setting it higher means the backup runs more often, which may cost less in electricity but more in fuel. Your installer can adjust this threshold based on your local climate and energy costs.

Comparing heat pump efficiency to other heating systems in winter

Even at reduced efficiency, an air-source heat pump in cold weather typically uses less energy than electric resistance heating or a standard gas furnace. A heat pump at 50% capacity in 0°F weather still converts electricity to heat more efficiently than a baseboard heater or furnace. The comparison changes if you have access to cheap natural gas; a gas furnace may cost less to operate on the coldest days. But in regions with high gas prices or where gas is not available, a heat pump with backup electric heat usually wins on operating cost even in winter.

The efficiency advantage of a heat pump shrinks as temperature falls, but it does not disappear. Over a full heating season in a cold climate, a heat pump typically uses 30% to 50% less energy than electric resistance heating and 20% to 40% less than a standard gas furnace, when you account for the mix of mild, moderate, and cold days. The coldest days pull the average down, but they are a small fraction of the heating season.

Sizing and installation factors that affect cold-weather performance

A heat pump that is undersized for your home's heating load will struggle more in cold weather. If the system cannot deliver enough heat even at full capacity, it will rely on backup heating for longer periods. Proper sizing means the heat pump can meet your heating needs on a design day (typically the coldest day your area experiences in an average winter) without running backup heat continuously. An oversized heat pump wastes money and cycles on and off inefficiently.

Installation quality also matters. Poor ductwork sealing, inadequate insulation around refrigerant lines, or incorrect refrigerant charge all reduce efficiency, especially in cold weather when the system is already working harder. A may have access to installer will test the system's performance and adjust refrigerant charge to match your local climate. If you are replacing an existing furnace with a heat pump, ask the installer whether your ductwork needs sealing or your home needs additional insulation before the heat pump goes in.

Frequently Asked Questions

Do heat pumps stop working when it freezes outside?

No. A heat pump continues to extract heat from air even at 0°F or below. It works less efficiently and delivers less heating output, but it does not shut down. Most systems include defrost cycles that melt ice buildup on the outdoor unit every 30 to 90 minutes during freezing weather, which temporarily reduces heating output but keeps the system running.

What temperature is too cold for a heat pump?

Standard air-source heat pumps can operate down to about -13°F, though efficiency is very poor at that point. Cold-climate models are rated to operate at -22°F or lower. Below those thresholds, the system may not start or may shut down automatically for safety. In practice, backup heating handles the load on the coldest days, so the heat pump rarely needs to operate at its absolute temperature limit.

Will a heat pump cost more to run in winter than my old furnace?

Not usually. Even with reduced efficiency in cold weather, a heat pump typically costs less to operate than electric resistance heating or a standard gas furnace over a full heating season. On individual very cold days, backup heating may cost more than a furnace would, but those days are rare. Compare your local electricity and gas prices with your installer's efficiency estimates for your specific climate to get a realistic picture of winter operating costs.

Is a cold-climate heat pump worth the extra cost?

In regions where winter temperatures regularly drop below 10°F, a cold-climate heat pump often pays for itself through lower heating costs over 5 to 10 years. In milder climates, a standard heat pump with backup heat is usually the better value. Ask your installer to model both options using your local climate data and energy rates.

Can I use a heat pump in a very cold climate without backup heating?

A ground-source heat pump can work without backup heating in most cold climates because it maintains consistent efficiency. An air-source heat pump without backup will struggle on the coldest days and may not reach your target temperature. Most cold-climate air-source installations include backup heating for this reason, even though it adds cost.