Heat Pump Temperature Range: How Cold Can a Heat Pump Work?

Operating range at a glance

Ranges are typical; each model's limits are in its engineering data. "Cutoff" means the outdoor unit stops heating, either because it physically cannot or because the controls lock it out in favor of backup heat.

Why capacity drops as it gets colder

A heat pump moves heat from outdoor air into the house. The colder the outdoor air, the lower the refrigerant's boiling temperature in the outdoor coil must be, the less dense the vapor the compressor draws in, and the less refrigerant it moves per stroke. Output falls just as the house needs more heat.

A standard unit rated at 36,000 BTU/h at 47 °F might deliver around 20,000 to 24,000 BTU/h at 17 °F and less still at 5 °F. A cold-climate unit uses a variable-speed compressor that can speed up, often with vapor injection, to hold much of its rated output. The NEEP cold-climate specification asks for a COP of at least 1.75 at 5 °F, and listed units commonly hold 70% or more of their rated capacity at that temperature.

Efficiency also falls with temperature, but stays above electric resistance heat (COP 1.0) across nearly the whole operating range. See heat pump efficiency by temperature and the COP calculator.

The balance point and backup heat

The balance point is the outdoor temperature where the heat pump's output exactly matches the house's heat loss. Above it, the heat pump handles everything alone. Below it, something else has to fill the gap.

• Electric resistance strips in the air handler: simple and reliable, but they run at COP 1, so they are expensive to rely on for long periods.
• Dual fuel: a gas or propane furnace takes over below a set outdoor temperature. Compare costs with gas vs electric heating.
• Oversizing the heat pump slightly in cold climates, with a variable-speed unit that can modulate down in mild weather, to push the balance point lower.

A properly selected system in a cold climate puts the balance point somewhere around 0 to 20 °F depending on the house and the equipment. The heat pump sizing calculator helps find that balance.

Defrost cycles in cold, damp weather

Between roughly 20 and 40 °F with high humidity, the outdoor coil runs below freezing and collects frost. Every so often the heat pump reverses to cooling mode for a few minutes to melt it. During defrost you may see steam rising from the outdoor unit and feel cooler air from the vents unless backup heat is staged on. This is normal. A unit that stays encased in ice, or defrosts constantly, needs service.

Keep the outdoor unit raised above typical snow depth and clear of drifts, and make sure meltwater can drain away rather than refreezing under the coil.

Cooling-side limits

In cooling mode, most residential heat pumps and air conditioners are rated at 95 °F and can operate to around 115 °F outdoor temperature, with some extended to 120 to 125 °F. Capacity and efficiency fall as outdoor temperature rises because the condenser has to reject heat to hotter air. Units in direct afternoon sun or with blocked airflow reach high-pressure trips sooner; see outside AC unit not running.

At the low end, many units should not run in cooling below about 55 to 65 °F outdoors unless they have low-ambient controls, which matters for server rooms and some mini-split applications.

Is a heat pump right for your climate?

1. Find your area's winter design temperature (the temperature the house should be able to handle 99% of the hours in a year).
2. Get a Manual J heat loss at that temperature.
3. Check the heat pump's capacity table at that temperature, not just the rated 47 °F figure.
4. Decide how much backup heat you want for colder snaps and outages.
5. Compare running costs using the heat pump running cost guide.

In most of the US, including much of the northern tier, a correctly sized cold-climate heat pump can carry the full heating load for most of the season.

Frequently asked questions