Heat pumps lose efficiency below 32°F and stop heating altogether around 0°F
Most air-source heat pumps—the kind mounted on your exterior wall or in your yard—begin to struggle when outdoor temperature drops below 32°F (0°C). Below that point, the refrigerant in the system has a harder time absorbing heat from the cold air, so your pump works longer to deliver the same warmth indoors. By the time you reach 0°F (-18°C), most standard heat pumps cannot extract enough heat to keep up with your home's demand and will switch to electric resistance heating (essentially a backup heater) to maintain your indoor temperature.
The exact cutoff varies by model. Some newer cold-climate heat pumps are engineered to work down to -13°F (-25°C) or lower, but they are more expensive and less common. If you live somewhere that regularly dips below freezing, the temperature rating of your specific unit matters more than a general rule.
Key Takeaways
- Standard heat pumps lose heating power below 32°F and typically cannot heat your home at all below 0°F without switching to backup electric heat.
- Cold-climate heat pumps are designed to work in temperatures as low as -13°F but cost significantly more than standard models.
- When your heat pump switches to electric resistance heating, your energy bills rise sharply because electric heating is much more expensive to run.
- Defrost cycles—when the system reverses to melt frost off the outdoor coil—also reduce heating output during cold weather.
- If you live in a climate with frequent freezing temperatures, a heat pump paired with a backup furnace or boiler is more practical than relying on the pump alone.
Why cold air makes heat pumps less effective
A heat pump works by moving heat from outside air into your home, even when that air feels cold to you. But as outdoor temperature drops, there is less heat available to extract. Think of it like trying to wring water from a damp cloth versus a dry one—the process gets harder the drier the cloth becomes.
The refrigerant inside your heat pump has a boiling point. In cold weather, the outdoor coil (the part that sits outside) becomes so cold that the refrigerant cannot boil efficiently. The compressor has to work much harder and longer to move what little heat is available. At some point—usually around 0°F—the system straightforward cannot extract heat fast enough to match the heat your home is losing through walls, windows, and doors.
How defrost cycles drain heating during winter
When outdoor temperature is near or below freezing, moisture in the air condenses on your heat pump's outdoor coil and freezes solid. This frost acts like insulation, blocking the coil from absorbing any heat at all. To fix this, your heat pump automatically reverses itself into cooling mode for a few minutes—running backwards to warm up the outdoor coil and melt the frost away.
During a defrost cycle, your home loses heat instead of gaining it. The system pulls warmth from inside your house to melt the ice outside. These cycles happen more and more often as temperature drops, eating into your heating output. On a day when your heat pump is already struggling, defrost cycles can make the difference between staying warm and needing to switch on your backup heater.
Electric resistance heating kicks in when the pump cannot keep up
Most heat pump systems include a backup electric heater—either built into the indoor unit or installed as a separate furnace. When outdoor temperature falls below your heat pump's rated minimum, or when the pump cannot heat your home fast enough on a very cold day, this backup automatically turns on.
Electric resistance heating works, but it is expensive. It uses roughly three times as much electricity as a heat pump to produce the same amount of warmth. If your backup heater runs for hours or days during a cold snap, your electric bill will spike noticeably. This is why heat pump owners in cold climates often see their winter bills jump during the coldest weeks—they are paying for electric heating, not heat pump heating.
Cold-climate heat pumps are built to work in freezing weather
Manufacturers now make cold-climate heat pumps specifically designed to heat homes in places where temperature regularly drops well below freezing. These units use different refrigerants, larger outdoor coils, and more powerful compressors. A quality cold-climate model can deliver useful heating down to -13°F (-25°C) or even lower, depending on the brand and model.
The trade-off is cost. A cold-climate heat pump typically costs 20 to 40 percent more than a standard model. Whether that premium makes sense depends on your local climate, your current heating system, and how many days per year you actually need heating below 0°F. In a place like Minnesota or upstate New York, a cold-climate pump paired with a backup furnace can be practical. In a place where freezing weather is rare and brief, a standard heat pump with a gas furnace backup is usually more economical.
Pairing a heat pump with a furnace or boiler for cold climates
The most reliable setup for a cold climate is a hybrid system: a standard or cold-climate heat pump that handles heating when temperature is above freezing, paired with a gas furnace or boiler that takes over when it gets too cold. Your system automatically switches between them based on outdoor temperature.
This approach lets you use the heat pump—which is efficient—during the shoulder seasons (fall and spring) and mild winter days, then switch to your furnace when the cold arrives. You get the efficiency benefit of the heat pump without the high electric bills that come from running backup electric heat. If you are replacing an old furnace anyway, adding a heat pump on top of it can lower your overall heating costs even in a cold climate, because the pump handles so many of the heating days.
How to know your heat pump's cold-weather rating
Your heat pump's specifications should list a minimum operating temperature or balance point. The balance point is the outdoor temperature at which the heat pump alone can no longer keep up with your home's heat loss, and your backup heater turns on. This is usually between 25°F and 40°F for a standard unit, and lower for a cold-climate model.
You can find this information in your owner's manual, on the nameplate attached to the outdoor unit, or by calling your installer. Knowing this number helps you understand when to expect your backup heater to run and gives you a realistic picture of your winter heating costs. If your balance point is 35°F and your area averages 20°F for three months straight, your backup heater will run a lot.
Frequently Asked Questions
Will my heat pump be damaged if it runs in very cold weather?
No. Modern heat pumps have built-in safety controls that prevent damage. However, running a standard heat pump below its rated minimum temperature forces it to work inefficiently and triggers your backup electric heater, which is expensive. Cold-climate heat pumps are designed to handle low temperatures safely and efficiently.
Can I use a heat pump as my only heating system if I live somewhere cold?
Only if you install a cold-climate model rated for your area's lowest temperatures, and even then you should have a backup plan. A standard heat pump alone in a cold climate will rely heavily on expensive electric resistance heating. A furnace or boiler backup is more practical and economical.
What temperature should I set my thermostat to in winter to save money?
Lowering your thermostat by 7 to 10 degrees for 8 hours per day can reduce heating costs by 10 to 15 percent. However, if you lower it so much that your backup electric heater kicks in, you lose that savings. The sweet spot is usually 68°F during the day and 62°F at night, adjusted based on your comfort and your system's balance point.
Does humidity affect how cold a heat pump can operate?
Yes. Dry cold is easier for a heat pump to work with than wet cold. In very humid climates, frost builds up faster on the outdoor coil, triggering more frequent defrost cycles and reducing heating output. This is one reason cold-climate heat pumps perform better in dry climates than in humid ones.
Should I turn off my heat pump in winter and use only my furnace?
No. Even in winter, your heat pump will run efficiently on mild days and use less energy than your furnace. Let your system switch automatically between the two. Manually switching them wastes the efficiency benefit of the heat pump and can confuse your thermostat's controls.