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

A heat pump can heat your home when it is freezing outside, but not as efficiently as it does in mild weather. Most air-source heat pumps—the most common type for homes—continue to pull heat from outside air even at 0°F or below, though the amount of heat they extract shrinks significantly. At around 25°F to 35°F, many heat pumps begin to lose noticeable heating capacity. Below that point, they often switch on a backup heating system (usually electric resistance heat) to meet your home's full heating demand, which costs more to run.

The colder it gets, the harder a heat pump must work to extract heat from outside air. This is why manufacturers publish a balance point—the outdoor temperature at which a heat pump can no longer meet your heating needs alone and your backup system kicks in. For standard air-source models, this is often between 25°F and 40°F, depending on the unit's design and your home's insulation. Ground-source (geothermal) heat pumps perform better in extreme cold because they draw heat from underground, where temperatures stay more stable year-round.

Key Takeaways

  • Air-source heat pumps continue to heat below freezing but lose efficiency as temperature drops, typically becoming less effective below 35°F.
  • Most heat pumps set up a backup heating system (electric resistance or gas) when outdoor temperature falls below their balance point, usually between 25°F and 40°F.
  • Ground-source heat pumps maintain better performance in cold climates because they extract heat from stable underground temperatures rather than outdoor air.
  • Cold-climate heat pump models are designed to work down to 0°F or lower and cost more upfront but reduce reliance on backup heat in freezing regions.
  • Your heating bills will rise in winter because backup systems are less efficient than the heat pump itself, especially during extended cold snaps.

Why heat pump efficiency drops in cold weather

A heat pump moves heat from one place to another using refrigerant and a compressor. In heating mode, it pulls heat from outdoor air and moves it indoors. The problem: as outdoor air gets colder, there is less heat available to extract. The compressor must work harder to pull that smaller amount of heat, using more electricity in the process. This is why a heat pump's heating output (measured in BTU) declines as the outdoor temperature falls.

At the same time, your home loses heat faster when it is very cold outside, so you need more heating capacity just when the heat pump is producing less. This mismatch is why backup heat turns on. Most homes with heat pumps have either an electric resistance heating element (built into the system) or a gas furnace that runs alongside the heat pump. When the heat pump cannot keep up, the backup system fills the gap—but it costs significantly more to operate than the heat pump itself.

Understanding your heat pump's balance point

The balance point is the outdoor temperature at which your heat pump's heating output equals your home's heating demand. Below that temperature, backup heat is needed. For a standard air-source heat pump in an average home, the balance point is typically 25°F to 40°F. Above the balance point, the heat pump alone can meet your heating needs. Below it, backup heat runs, and your heating costs rise.

Your balance point depends on three things: the heat pump model's capacity, your home's insulation and air sealing, and how cold it gets where you live. A well-insulated home with a high-capacity heat pump may have a balance point near 20°F. A poorly insulated home with a smaller unit might have a balance point near 45°F. You can find your specific balance point in your heat pump's technical documentation or by asking your installer.

Cold-climate heat pumps for freezing regions

Manufacturers now produce cold-climate heat pumps designed to work efficiently down to 0°F or even lower. These units use enhanced compressors, larger coils, and better refrigerants to extract heat more effectively in extreme cold. They cost 15 to 25 percent more than standard models but reduce the amount of backup heat needed during winter, which can offset the higher upfront cost over time through lower heating bills.

Cold-climate models are worth considering if you live in a region where temperatures regularly drop below 20°F for weeks at a time. They are less useful in mild climates where freezing weather is rare or brief. If you are replacing an old heating system in a cold region, a cold-climate heat pump paired with a backup system (gas furnace or electric resistance) is often more cost-effective than a furnace alone, especially when you factor in heating and cooling together.

Ground-source heat pumps perform better in extreme cold

A ground-source heat pump (also called geothermal) extracts heat from the ground or groundwater rather than outdoor air. Underground temperatures stay between 45°F and 55°F year-round in most regions, even when air temperature is far below zero. This means a ground-source heat pump maintains steady heating capacity throughout winter and rarely needs backup heat, even in the coldest climates.

The trade-off is cost and installation complexity. Ground-source systems require drilling or trenching to install underground loops, which can cost $15,000 to $30,000 or more depending on your property and soil conditions. They are most practical for new construction or when you are replacing a failed heating system and can justify the upfront investment through long-term energy savings. In cold climates where backup heat would run frequently, a ground-source system can pay for itself within 10 to 15 years through reduced heating bills.

What happens to your heating bills when backup heat runs

When outdoor temperature drops below your heat pump's balance point, backup heat turns on automatically. If your backup is electric resistance (the most common setup), your heating costs jump significantly because resistance heat is about three times more expensive to operate than a heat pump. If your backup is a gas furnace, costs rise but not as dramatically. Either way, your winter heating bill will be higher during cold snaps than during mild winters.

This is normal and expected. Heat pump owners in cold climates should budget for higher heating costs during January and February. The overall annual cost is usually still lower than a furnace-only system because the heat pump runs efficiently during fall and spring, but monthly bills during the coldest weeks will reflect the backup system's operation. Improving your home's insulation and air sealing can lower your balance point, meaning the heat pump stays in control longer before backup heat is needed.

How to maximize heat pump performance in winter

Seal air leaks around windows, doors, and penetrations where pipes and wires enter your home. Air leaks force your heating system to work harder and lower the temperature at which backup heat kicks in. Insulate your attic to at least R-38 and your basement walls to R-10 or higher. These upgrades reduce heating demand, which means your heat pump can meet more of your needs without backup heat running.

Keep your heat pump's outdoor unit clear of snow and ice buildup, which blocks airflow and reduces heating capacity. Most modern units have a defrost cycle that melts ice automatically, but heavy snow should be brushed away by hand. Check your system's air filter monthly during heating season and replace it if it is visibly dirty—a clogged filter reduces airflow and heating output. If your heat pump has a programmable thermostat, avoid setting it to switch to backup heat manually; let the system manage the switch automatically based on outdoor temperature.

Frequently Asked Questions

Can a heat pump heat a home at 0°F?

Yes, a standard heat pump can extract heat from 0°F air, but it will produce very little heating capacity and backup heat will almost certainly be running. A cold-climate heat pump model is designed to work more efficiently at 0°F and will reduce backup heat use, but even cold-climate models typically need backup heat at extreme temperatures.

Will my heat pump freeze up in winter?

Modern heat pumps have a defrost cycle that prevents ice buildup on the outdoor coil. The system detects frost and reverses briefly to melt it. You may see steam or water dripping from the outdoor unit during defrost—this is normal. Heavy snow should be cleared by hand, but the system handles typical frost on its own.

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

In very cold climates where backup heat runs frequently, a furnace may have lower monthly heating bills during winter. However, a heat pump heats and cools, so your annual energy cost is usually lower because you avoid air conditioning bills. Compare your total annual heating and cooling costs, not just winter heating, to get an accurate picture.

What outdoor temperature should I set my thermostat to switch to backup heat?

Let your heat pump's automatic controls manage the switch. Most systems are programmed to switch at the balance point (typically 25°F to 40°F). Manually forcing backup heat at a higher temperature wastes money. If you want to adjust when backup heat runs, ask your installer about reprogramming the balance point.

Do I need a different thermostat for a heat pump in cold weather?

A standard programmable or smart thermostat works fine with a heat pump in cold weather. The thermostat straightforward tells the system what temperature you want; the heat pump and backup system handle the rest automatically. Some smart thermostats offer features like scheduling and remote control, but these are optional conveniences, not requirements for cold-weather operation.