Heat pumps in cold weather

Air-source heat pumps keep working in cold weather, but two things drop as it gets colder: how much heat the unit can deliver (capacity) and how efficiently it does it (COP (coefficient of performance)). How far they drop depends on the specific model. Cold-climate models are designed to hold more capacity at low temperatures, and they are tested and listed at 5°F.

Why output falls in the cold

There is still heat in cold air. Natural Resources Canada (NRCan) notes that "the heat content of air at -18°C equates to 85% of the heat contained at 21°C."^{[Source 1]} The problem is the temperature difference. The colder it is outside, the further the heat pump has to lift heat to get it indoors, which takes more work per unit of heat. NRCan gives typical ranges:^{[Source 1]}

Outdoor temperature	Typical air-source COP range (NRCan)
8°C (46°F)	2.0 to 5.4
-8°C (18°F)	1.1 to 3.7

A COP of 2 means two units of heat delivered for each unit of electricity. Electric resistance heat has a COP of 1: the DOE notes that electric resistance gives about 3,400 Btu per kWh,^{[Source 6]} which is the energy content of a kWh. So even at a modest COP, the heat pump uses less electricity than resistance heat for the same heat.

At the same time, the house loses heat faster as it gets colder. Falling capacity meets rising load at the thermal balance point. Below it, a second heat source is needed to keep up.

Minimum operating temperature

Most air-source heat pumps also have a cutoff temperature below which they stop running. NRCan: "For newer models, this can range from between -15°C to -25°C" (5°F to -13°F).^{[Source 1]} The operating range for a specific model is in the manufacturer's specifications.

What a 5°F rating means

The federal test procedure, Appendix M1, includes an optional "very low temperature" heating test at 5°F outdoors (the H4 test).^{[Source 7]} ENERGY STAR measures its cold-climate COP and capacity requirements with the H4₂ version of that test, and NEEP asks for COP at 5°F "at maximum capacity operation."^{[Source 2][Source 3]} Two numbers come out of it:

• COP at 5°F tells you efficiency at that temperature.
• Capacity at 5°F, compared with the rated capacity at 47°F, tells you how much output the unit keeps. A unit rated 36,000 Btu/h at 47°F that keeps 70% would deliver about 25,200 Btu/h at 5°F.

A 5°F rating is one data point. For a real house, the installer should compare the heat pump's capacity at your local design temperature to your Manual J heating load, using the manufacturer's extended performance tables.

ENERGY STAR Cold Climate

ENERGY STAR's air source heat pump specification, Version 6.2 (revised February 2, 2026), has a Cold Climate designation. Its requirements:^{[Source 2]}

Requirement	Non-ducted split	Ducted split
SEER2	15.2 or higher	15.2 or higher
HSPF2	8.5 or higher	8.1 or higher
COP at 5°F	1.75 or higher	1.75 or higher
Capacity at 5°F	At least 70% of capacity at 47°F	At least 70% of capacity at 47°F

It also requires a controls verification procedure.^{[Source 2]}

NEEP cold-climate specification

The Northeast Energy Efficiency Partnerships (NEEP) publishes its own Cold Climate Air Source Heat Pump Specification and a public product list.^{[Source 3][Source 5]} Version 4.0, effective January 1, 2023, requires:^{[Source 3]}

• a variable-capacity compressor: "three or more distinct operating speeds, or continuously variable"
• "COP at 5°F ≥ 1.75 at maximum capacity operation"
• non-ducted: HSPF2 of 8.5 or higher and SEER2 of 15 or higher
• ducted: HSPF2 of 7.7 or higher and SEER2 of 14.3 or higher

Version 4.0 does not include a 5°F-to-47°F capacity ratio. That 70% test is in the ENERGY STAR Cold Climate criteria, not in NEEP's. NEEP's 2026 revision memo confirms that "NEEP has not added those requirements."^{[Source 4]}

The NEEP list's value for buyers is the data it reports: minimum, rated and maximum capacity and COP at 47°F, 17°F and 5°F, and at the lowest temperature the manufacturer catalogs.^{[Source 3]} That is the information needed to estimate a balance point.

Changes coming, as of October 2026

• NEEP Version 5.0. In a memo released July 7, 2026, NEEP proposed that products qualify by holding ENERGY STAR Cold Climate certification or being listed as compliant with CEE Tier 1, Path A, and proposed dropping the variable-capacity requirement. NEEP gave December 2026 as the timeline for the final version.^{[Source 4]}
• NEEP list data. NEEP's memo says the list's data comes "exclusively" from AHRI since February 2026; the list site says the transition to AHRI data completed April 1 and that some eligible products may still be missing.^{[Source 4][Source 5]}

Check the dates on these documents before relying on a specific threshold.

Backup heat in cold weather

Even a cold-climate heat pump may need backup on the coldest days, depending on the house and how the system was sized. See Heat pump backup heat and lockout temperatures, Dual fuel and hybrid heat pump systems and Heat pump defrost cycles.