Heat pumps work in cold weather, but their output drops as temperatures fall
Heat pumps do not stop working when it gets cold, but they become less efficient. A heat pump pulls warmth from outside air even when that air is freezing, and moves it indoors. The colder it gets, the harder the unit has to work to extract that heat, and the less heat it can deliver to your home per unit of electricity used.
Most air-source heat pumps — the most common type — lose roughly half their heating capacity somewhere between 25°F and 35°F. Below that point, many systems switch to electric resistance heating (essentially a space heater) to make up the difference. That backup heat is much more expensive to run. In regions where winter temperatures regularly drop below 20°F, a heat pump alone may not be your most cost-effective heating choice.
Ground-source heat pumps, which pull heat from the earth rather than the air, stay efficient in cold weather because ground temperature stays relatively stable year-round. But they cost significantly more to install and are not practical for most homeowners.
Key Takeaways
- Air-source heat pumps continue to operate in freezing temperatures but deliver less heat as outdoor temperature drops.
- Most air-source heat pumps lose about half their heating output between 25°F and 35°F, depending on the model and outdoor conditions.
- When outdoor temperature falls below the heat pump's effective range, the system switches to electric resistance heating, which costs more to run than the heat pump itself.
- Ground-source heat pumps maintain efficiency in cold weather but require expensive underground installation that is not practical for most homes.
- In climates where winter temperatures regularly stay below 20°F, pairing a heat pump with a backup heating system is usually more cost-effective than relying on the heat pump alone.
How heat pumps extract warmth from cold air
A heat pump works by circulating refrigerant through a cycle that absorbs heat from outside and releases it indoors. Even air at 0°F contains heat energy — it is just less of it than warmer air holds. The refrigerant in the outdoor coil is kept even colder than the outside air, so heat still flows into it.
The compressor then pressurizes that refrigerant, which raises its temperature further, and the indoor coil releases that heat into your home. The process works the same way whether it is 50°F or 10°F outside — the physics does not change. What changes is the amount of heat available to extract and how much work the compressor must do to extract it.
Think of it like wringing water from a wet towel versus a damp one. You can still wring the damp towel, but you get less water out and have to squeeze harder. The colder the air, the "damper" it is in terms of available heat, and the more the compressor has to work.
When heat pumps lose efficiency and switch to backup heat
The temperature at which a heat pump stops being the primary heating source varies by model and design. Most modern air-source heat pumps are rated to operate down to around 0°F, but their heating output at that temperature is only a fraction of what they deliver at 47°F (the standard rating temperature). Manufacturers publish a heating output curve that shows this decline.
When the outdoor temperature drops below what the heat pump can efficiently handle, the system automatically activates electric resistance heating — usually a strip heater in the indoor unit or a separate furnace. This backup heat is reliable and keeps your home warm, but it draws much more electricity per unit of heat produced than the heat pump does. In some systems, the switchover happens at a set temperature (often 35°F). In others, it happens when the heat pump cannot keep up with demand.
You will notice the difference on your electric bill. A night when the heat pump runs alone might cost $3 to $5 in heating. A night when the backup heat kicks in might cost $8 to $15 for the same temperature drop, depending on your local electricity rates and how long the backup runs.
Regional differences in heat pump performance
Heat pump economics vary sharply by climate. In the Pacific Northwest, upper Midwest, and Northeast — where winter temperatures often dip below 20°F — a heat pump alone usually cannot meet heating demand without expensive backup heat running frequently. In those regions, homeowners often pair a heat pump with a gas furnace or keep an existing furnace as backup.
In milder climates like the Southeast and Southwest, where winter temperatures rarely fall below 30°F, a heat pump can handle most or all heating needs. The backup heat runs rarely or not at all, and the heat pump's lower operating cost over the heating season makes it the most economical choice.
If you live in a region where winter temperatures regularly stay above 35°F, a heat pump alone is usually sufficient and cost-effective. If winter temperatures regularly drop below 25°F, plan on a backup heating system and budget for the cost of running it during the coldest weeks.
Frost buildup and defrost cycles in freezing weather
When outdoor humidity is high and temperature is near freezing, frost accumulates on the outdoor coil. This frost acts as insulation and blocks airflow, reducing the heat pump's ability to extract warmth. To handle this, heat pumps have a defrost cycle that reverses the refrigerant flow temporarily, warming the outdoor coil and melting the frost.
During defrost, the indoor coil gets cold and the heat pump stops heating your home for a few minutes. In very cold, humid conditions, defrost cycles can run frequently — sometimes every 20 to 30 minutes — which reduces overall heating output and increases energy use. Some newer heat pumps use sensors to defrost only when needed, rather than on a timer, which reduces wasted cycles.
If you notice your heat pump cycling on and off frequently on cold, humid mornings, defrost cycles are likely the reason. This is normal operation, not a malfunction.
Choosing between a heat pump alone and a hybrid system
A heat pump alone makes sense if you live in a climate where winter temperatures rarely drop below 30°F, or if you are replacing an electric resistance heating system and can accept higher heating costs on the coldest days. The heat pump will still save money over the year because it runs efficiently during fall and spring.
A hybrid system — heat pump plus gas furnace or electric furnace — makes sense if winter temperatures regularly drop below 25°F. The heat pump handles the bulk of heating when conditions are mild, and the furnace takes over on the coldest days. This setup costs more upfront but usually saves money over time because the cheaper heating source runs when it is most needed.
Some homeowners keep an existing furnace and add a heat pump for cooling and mild-weather heating. This avoids the cost of replacing a working furnace and lets the heat pump reduce heating costs during shoulder seasons. The furnace still runs on the coldest days, but less often than it would without the heat pump.
Maintenance and winterization for cold-weather performance
A heat pump that is not maintained properly loses efficiency faster in cold weather. Before winter, have the system serviced: check refrigerant charge, clean the outdoor coil, inspect the compressor, and test the defrost cycle. A unit that is low on refrigerant will struggle even more in cold weather.
Keep the outdoor unit clear of snow, ice, and debris. If snow piles up around the unit, it blocks airflow and forces the defrost cycle to run more often. If ice forms on the coil and does not melt during defrost, the system may shut down to prevent damage. In heavy snow climates, some homeowners build a straightforward shelter around the outdoor unit to reduce snow accumulation while still allowing airflow.
Check that the indoor unit's air filter is clean. A clogged filter reduces airflow and makes the system work harder, which is especially important in cold weather when efficiency is already reduced.
Frequently Asked Questions
At what temperature do heat pumps stop working?
Most air-source heat pumps continue to operate down to 0°F or below, but their heating output drops sharply as temperature falls. Below 25°F to 35°F, depending on the model, the system usually switches to electric resistance backup heat. Below 0°F, some units may shut down to prevent compressor damage, though this is rare in modern systems.
Will a heat pump keep my house warm if it is 10 degrees outside?
Yes, but the heat pump alone may not keep up with demand. At 10°F, most heat pumps deliver only 30 to 50 percent of their rated heating capacity. The backup heating system (if you have one) will run to make up the difference. If you have no backup heat, the heat pump will run continuously but may not maintain your desired indoor temperature.
Is it cheaper to run a heat pump or a furnace in winter?
A heat pump is cheaper to run when outdoor temperature is above 30°F to 35°F. Below that, electric resistance backup heat or a gas furnace becomes more cost-effective. In a hybrid system, the heat pump runs during milder weather and the furnace takes over on the coldest days, which minimizes heating costs over the season.
Can frost damage a heat pump in winter?
Frost itself does not damage the heat pump — the defrost cycle is designed to handle it. However, if the defrost cycle fails or runs too often, the coil can ice over and restrict airflow, which may cause the system to shut down. Regular maintenance prevents defrost problems.
Do I need to cover my heat pump in winter?
No. Covering the outdoor unit blocks airflow and prevents the defrost cycle from working properly. Clear snow and ice away by hand if it accumulates, but do not cover the unit. A shelter that allows airflow is acceptable in heavy snow climates.