A modern cold-climate heat pump is a heating system that can work in cold weather, including freezing temperatures and, with the right model, below 0°F. ENERGY STAR cold-climate models are tested at 5°F. A 2023 field-validation paper cited below examines how these systems perform in cold climates.
As outdoor temperatures fall, a heat pump loses some heating capacity and efficiency. In severe cold, a properly designed system may use electric backup heat or a gas furnace.
Cold-Weather Heat Pumps at a Glance
| Question | Short answer |
|---|---|
| Do heat pumps work below 32°F? | Yes. Cold-climate models are designed for subfreezing weather. |
| Will a heat pump work at 5°F? | Yes. ENERGY STAR cold-climate models are tested at 5°F. |
| Will it work below 5°F? | Often, but performance depends on the model and installation. |
| Does a heat pump need backup heat? | Not always. Backup heat can help during extreme cold or when it costs less to run than the heat pump. |
| Are geothermal heat pumps better in cold weather? | They are less affected by outdoor air temperature because they draw heat from the relatively stable ground. |
How Can a Heat Pump Heat a Home When It Is Freezing Outside?
A heat pump moves heat rather than creating heat by burning fuel. Even cold outdoor air contains thermal energy. In heating mode, an air-source heat pump extracts that energy, raises its temperature with a compressor, and transfers it indoors.
When the outdoor temperature drops, less heat is available in the air. The compressor also has to work harder to raise that heat to a useful indoor temperature. Heating capacity and efficiency therefore decline in very cold weather.
The system does not suddenly stop working at 32°F or 20°F. It may run longer, use more electricity, or turn on supplemental heat to meet the home's heating demand.
How Cold Can an Air-Source Heat Pump Operate?
There is no single temperature limit for every heat pump. The manufacturer's performance data matters more than a general cutoff.
ENERGY STAR's cold-climate designation requires a heat pump to:
- Achieve a coefficient of performance of at least 1.75 at 5°F.
- Retain at least 70% of its 47°F heating capacity at 5°F.
- Pass controls verification showing that the system reaches that performance during normal operation.
ENERGY STAR says certified cold-climate air-source heat pumps can continue operating below 5°F. At lower temperatures, pairing the system with backup heat may cost less or use less energy.
For a purchase decision, ask:
How much heating capacity does this specific model provide at my area's design temperature?
A unit's rating at 47°F does not show how much heat it will provide at 5°F or -10°F.
Why Does a Heat Pump Sometimes Use Backup Heat?
A heat pump may use supplemental heat when:
- Outdoor temperatures fall below the system's economical operating range.
- The home needs more heat than the heat pump can provide.
- The outdoor coil is defrosting.
- The thermostat is recovering from a large temperature setback.
- The system is undersized or the home has substantial heat loss.
Backup heat may come from electric resistance elements, a gas furnace, an oil furnace, or another heating system. A heat pump combined with a gas or oil furnace is called a dual-fuel or hybrid heating system. The heat pump handles much of the heating, while the furnace takes over when the temperature or energy prices make that choice more practical.
Backup heat does not necessarily mean the heat pump is failing. Many systems are designed to use it. Frequent or unexpected auxiliary heat use can point to poor sizing, inadequate insulation, duct problems, or a fault that needs inspection.
What Happens During a Defrost Cycle?
In damp conditions near freezing, frost can collect on the outdoor coil. Frost restricts airflow and reduces heat transfer, so the heat pump periodically enters a defrost cycle.
During defrost, the system temporarily sends heat to the outdoor coil to melt the frost. The outdoor fan may stop, steam may rise from the unit, and the system may briefly use auxiliary heat indoors. Defrost cycles are most relevant at roughly 20°F to 40°F, when outdoor moisture is more available.
A short defrost cycle is normal. Ice that remains on the outdoor coil is not. Snow, leaves, and other obstructions should also be cleared so the unit can move air and drain meltwater.
Are Cold-Climate Heat Pumps Efficient in Winter?
Yes, but winter efficiency depends on outdoor temperature, the equipment, installation quality, electricity prices, and the home's insulation.
A heat pump can deliver more heat energy than the electrical energy it consumes because it transfers heat instead of generating it directly. ENERGY STAR states that air-source heat pumps can deliver up to three times more heat energy than the electricity they use, although results vary with operating conditions.
Efficiency generally falls as temperatures become more extreme. Whether a heat pump costs less to operate than a furnace depends on local fuel and electricity prices. It may have a clear cost advantage over electric resistance, propane, or oil heating, while the comparison with natural gas varies by location and utility rates.
Air-Source Versus Geothermal Heat Pumps in Cold Weather
| Heat pump type | Cold-weather behavior |
|---|---|
| Air-source heat pump | Extracts heat from outdoor air. Capacity and efficiency decline as air temperature falls. |
| Ground-source or geothermal heat pump | Extracts heat from the ground, where temperatures are more stable than outdoor air. |
| Dual-fuel system | Uses the heat pump in moderate weather and a furnace during selected colder periods. |
Ground-source heat pumps are less exposed to sudden outdoor temperature changes because underground temperatures remain relatively stable. The U.S. Department of Energy states that temperatures below the surface are generally warmer than winter air and stay within a narrower range than outdoor temperatures.
Geothermal systems can perform well in cold climates, but they need buried ground loops, suitable site conditions, and a larger installation than an air-source system.
What Should You Look for in a Heat Pump for a Cold Climate?
Choose a system based on its low-temperature performance, not only its headline efficiency rating.
Ask the installer for:
- An ENERGY STAR Cold Climate model where available.
- Heating capacity at 47°F, 17°F, 5°F, and your local design temperature.
- The manufacturer's minimum operating temperature.
- The system's balance point, which is the temperature at which backup heat becomes necessary or more economical.
- A Manual J heat-loss calculation for the home.
- Correct matching of the outdoor unit, indoor coil, air handler, and thermostat.
- A plan for snow clearance, drainage, and outdoor-unit airflow.
- A backup heating plan if temperatures regularly fall below the heat pump's rated range.
ENERGY STAR recommends Manual J sizing and says that weatherizing the home can improve comfort and reduce energy use, especially in older houses.
Do Heat Pumps Work in Extreme Cold?
They can, but the equipment and system design determine the result. A standard heat pump may not provide all the heat a home needs during prolonged subzero weather. A cold-climate model, good insulation, correct sizing, and a suitable backup plan can provide reliable winter heating.
For a home in a severe winter climate, the main options are:
- A cold-climate heat pump sized to meet most or all of the home's design heating load.
- A heat pump with electric backup heat.
- A dual-fuel system that combines a heat pump with a gas or oil furnace.
- A geothermal heat pump when the site and budget support the installation.
Bottom Line
Heat pumps can heat homes in freezing weather and below 0°F when the model is suited to the climate. Their capacity and efficiency fall as temperatures drop, so the purchase decision should be based on low-temperature capacity, the home's heat loss, and the backup heating plan.
An installer should be able to show the unit's rated heating capacity at your local design temperature and explain when backup heat will run.