How Heat Pumps Handle Cold Climates, and When Backup Heat Kicks In

Yes, heat pumps work in cold climates: models built for the cold keep heating well below freezing, but their output and efficiency fall as the outdoor temperature drops. In a Department of Energy (DOE) field study of 22 cold-climate prototypes, built to keep their full capacity at 5°F (a stricter bar than today's labels), the median efficiency of the heat pump running on its own between 0°F and 5°F was a coefficient of performance (COP) of 1.9, meaning 1.9 units of heat for every unit of electricity. In the coldest temperature range with enough data, -10°F to 0°F, electric backup heat was engaged about a quarter of the time. The federal 25C tax credit no longer applies to units installed since January 1, 2026, so buyers now pay the full price up front, and a model's cold-weather performance and running cost are worth checking before signing.

This article is general education, not financial or engineering advice. Prices, incentives and equipment vary by home and state.

Key takeaways

• Cold-climate certification asks for a COP of at least 1.75 at 5°F under both ENERGY STAR and NEEP rules, and ENERGY STAR also requires the unit to keep at least 70% of its 47°F heating capacity at 5°F.
• In the DOE field study, with defrost and backup periods excluded, the median COP was 1.6 to 2.7 below 30°F and 1.9 at 0°F to 5°F. Backup elements were engaged about 25% of the time in the coldest bins with enough data (-10°F to 0°F).
• The balance point is the outdoor temperature below which the heat pump alone cannot meet the house's load. In the worked example below it is about 18°F for a unit that keeps 70% of its capacity at 5°F and is sized so its 47°F output equals the house's heat loss at 5°F.
• At January 2026 national average prices, heat from a COP 3.0 heat pump cost about $17 per million Btu against about $14 for a 95% efficient gas furnace and about $51 for electric resistance. The break-even COP against gas was about 3.6.
• The 25C credit does not apply to heat pumps placed in service after December 31, 2025. Any help now comes from state, utility or local programs, so check them before signing.

What it means for you

• Very cold winters (days below 0°F): look at the unit's capacity and COP at 5°F and at its lowest published operating temperature, and ask what backup heat the quote includes. See the sections on field results and the balance point.
• Replacing gas heat: at January 2026 national average prices, heat from a heat pump cost about 20% more than from a 95% efficient gas furnace at a COP of 3.0 and about 80% more at a COP of 2.0; it matched an 80% furnace at a COP of about 3.0. Your local electricity-to-gas price ratio decides. See the running-cost section.
• Replacing electric baseboard or resistance heat: a heat pump at COP 2 or better delivers each kWh of heat for half the electricity or less. The savings are larger here than against gas.
• Already own one: frequent "aux" heat on the thermostat in moderate cold is a sign worth investigating, because that is the expensive mode. Deep night setbacks and big setpoint jumps can also trigger it.

Heat pumps in cold climates

A heat pump moves heat from outdoor air into the house instead of making it. Colder air holds less usable heat, and the machine has to lift it across a bigger temperature gap, so COP falls with the temperature. Natural Resources Canada (NRCan) gives the typical range for air-source units as a COP of 2.0 to 5.4 at 8°C (about 46°F) and 1.1 to 3.7 at -8°C (about 18°F). It adds that newer models can have a minimum operating temperature of -15°C to -25°C (5°F to -13°F).

What the cold-climate labels require

NEEP also publishes a product list that follows its specification, and its reporting template asks makers for capacity and power at 47°F, 17°F and 5°F plus the "lowest cataloged temperature", the coldest outdoor temperature at which the maker publishes performance data. Defrost and drain-pan heater power are left out of those figures, so they are steady-state numbers. A label threshold at 5°F is a floor, not a promise for -10°F, which is why that last column is worth reading for your area.

What field tests measured

A large recent U.S. dataset is the Pacific Northwest National Laboratory report on the DOE challenge (January 2025). It followed 22 prototype units, sized with an ACCA Manual J load calculation, in the U.S. and Canada from winter 2022 to early fall 2024; the U.S. units were in occupied homes, and the Canadian ones in a mix of occupied and laboratory homes. Excluding periods of backup heat or defrost, median COPs at temperatures below 30°F were 1.6 to 2.7, and 1.9 in the 0°F to 5°F bin. Many sites had milder winters than normal, and only eight of the 22 recorded 10 or more hours of heating below 0°F, so the coldest results rest on a few homes.

An older Minnesota study by the Center for Energy and Environment (November 2017, equipment from the 2015 to 2017 winters) shows the extreme end. The ducted systems were set to lock out the heat pump below 10°F, so a propane furnace took over. The ductless units could run down to -13°F: between 0°F and -13°F, one had an average daily COP of 1.7 and another 1.3, and one unit kept operating with a COP above 1.0 at -19°F outdoor temperature. Weather-normalized annual heat-pump-only COPs at three of the four ducted sites were 2.75, 2.78 and 2.51.

Balance point and backup heat

As it gets colder, the heat pump's output falls while the house loses heat faster. NRCan defines the thermal balance point as the temperature below which the heat pump cannot meet the building's needs alone. Below it, a supplementary system covers the gap: resistance elements in the air handler or ducts, or a furnace in a dual-fuel setup. NRCan also describes an economic balance point, the temperature below which the supplementary system is cheaper to run than the heat pump, which depends on the electricity-to-fuel price ratio.

Illustrative example. A house loses 36,000 Btu/h at 5°F, and its loss falls in a straight line to zero at 65°F (39,000 Btu/h at 0°F). Its 3-ton heat pump delivers 36,000 Btu/h at 47°F and keeps 70% of that, 25,200 Btu/h, at 5°F, the ENERGY STAR minimum, with capacity changing in a straight line between the two points. The lines cross at about 17.6°F, so the balance point is roughly 18°F. At 5°F the backup must supply the missing 10,800 Btu/h; at 0°F, about 15,100 Btu/h.

If the heat pump runs at COP 1.9 at 5°F, it uses 25,200 ÷ 1.9 ≈ 13,260 Btu/h of electricity and the resistance backup uses 10,800 Btu/h at COP 1, so the whole system delivers 36,000 ÷ 24,060 ≈ 1.50 units of heat per unit of electricity. A unit that kept 100% of its capacity at 5°F, as the DOE challenge prototypes had to, and still ran at COP 1.9 would carry the same load alone at the full 1.9. The trade-off runs both ways: a full-capacity unit at COP 1.75 would still beat this system's 1.50, but one at COP 1.4 would not. On a cold day, check both the capacity a unit keeps and its COP at that temperature.

Auxiliary heat and emergency heat

The two thermostat settings are different. Per a Lennox support page, auxiliary heat is the second stage that turns on when the first stage (the heat pump) cannot meet demand; with an electric-heat air handler it runs alongside the heat pump, while in dual-fuel systems it shuts the heat pump off and runs alone. Emergency heat uses only the supplemental stage, without the heat pump. The auxiliary lockout temperature, the outdoor temperature at which backup is allowed to engage, is an installer setting; Lennox gives 40°F as an example, not a rule.

In the PNNL field data the backup elements were staged, with at least three stages per unit, and most units that used backup during defrost engaged only the first stage, around 5 kW. The median share of energy from auxiliary heat, excluding defrost, was around 11% at 5°F and 0% at the mildest temperatures with enough data. It rose at the coldest temperatures, although three of the four sites with data in the two lowest bins used more backup than the rest, so those bins may overstate the typical home.

Defrost and sizing

Frost builds on the outdoor coil in cold, humid conditions, and the unit briefly reverses to melt it. In the PNNL study defrost used the most energy between 5°F and 35°F, a median of 5% to 8% of total energy there. The outliers were sites that ran resistance heat during defrost and spent more time in defrost mode, one of them 16% of the time under 40°F against a study average of 5%.

Sizing sets where the balance point falls. NRCan says an undersized unit leans on the supplementary system more often, and an oversized one cycles on and off in mild weather, which costs comfort and wears the equipment. The NEEP specification makes the same point: meeting the performance numbers does not mean a product suits every application, and buyers should check building loads and capacity at the design temperature.

Running cost at winter prices

To compare heat sources, convert each fuel to dollars per million Btu (MMBtu) of heat delivered. EIA's conversion factors are 3,412 Btu per kWh, 1,036 Btu per cubic foot of natural gas and 100,000 Btu per therm.

Electric heat: $ per MMBtu = (price $/kWh × 293.1) ÷ COP
Gas furnace:   $ per MMBtu = (price $/Mcf ÷ 1.036) ÷ AFUE
Break-even COP = (price $/kWh × 293.1) ÷ gas $ per MMBtu

293.1 = kWh per million Btu (1,000,000 ÷ 3,412)
1.036 = MMBtu per 1,000 cubic feet (Mcf) of gas
Bill in therms? 1 therm = 100,000 Btu, so $ per therm × 10 = $ per MMBtu of gas
AFUE = furnace efficiency as a decimal (0.95 for a 95% furnace)

Illustrative example with January 2026 national averages. EIA's Electric Power Monthly (release of October 23, 2026, preliminary) puts residential electricity at 17.45 cents per kWh in January 2026. EIA's residential natural gas price (release of October 30, 2026) was $13.96 per Mcf. The table assumes the house needs 50 MMBtu of heat over the season, a round figure chosen for the example, not a typical home.

At these prices the heat pump has to reach a COP of about 3.6 to match a 95% gas furnace; against an 80% furnace the break-even falls to about 3.0. A heat pump at COP 3.0 therefore cost about 20% more per unit of heat than the 95% furnace ($17.05 against $14.18), while at COP 2.0 it still cost half of what resistance heat did. The comparison swings with the local price ratio, and the national average hides large differences between states. To try your own rates, use the running cost calculator.

Two cautions. The national gas price was $26.45 per Mcf in July 2026, nearly double January's, so use winter-month prices. For your own home, take the per-kWh and per-therm charges from a winter bill and leave out fixed monthly fees, which stay the same unless you close the gas account altogether (if you would, count the gas fee you save). And the table uses one COP for the whole season, while a real home's average blends milder days at higher COP with cold days near 1.5 to 2, as in the balance-point example.

Incentives as of November 2026

The federal 25C home improvement credit, worth up to $2,000 a year for a qualifying heat pump, ended for property placed in service after December 31, 2025, according to an IRS FAQ on Public Law 119-21. The IRS's own 25C page (last reviewed April 28, 2026) is worded less precisely, saying the credit covers improvements made "through December 31, 2025"; both point to the same cutoff. A unit installed in 2026 does not qualify even if it was paid for in 2025.

DOE's Home Energy Rebates page says the rebates are "now available in select states", names none, and sends readers to their state energy office for status and eligibility. Utility and local rebates also vary. Before you sign a quote, confirm in writing which programs are open, what they pay and what they require.

Frequently asked questions

How cold is too cold for a heat pump?

It depends on the model. NRCan says newer units can have a minimum operating temperature of -15°C to -25°C (5°F to -13°F), and in the Minnesota study one ductless unit kept running at -19°F, with a COP above 1.0. Many installations also set a lockout so that only the backup runs below a chosen temperature; the Minnesota ducted systems used 10°F. Compare the unit's lowest published temperature with your area's design temperature.

Do I need a backup furnace or electric strips?

It depends on the unit and your design temperature, and even strong units used some. The DOE challenge prototypes had to keep 100% of their capacity at 5°F, yet in the PNNL field data auxiliary heat still supplied a median of about 11% of heating energy at 5°F, and many units ran the first backup stage during defrost. For units that lose more capacity in the cold, backup covers the shortfall below the balance point. Ask the installer to show the load calculation, the temperature at which the proposed unit stops meeting it, and how often backup is expected to run at your design temperature.

Is a ground-source heat pump better in extreme cold?

Ground-source systems draw on ground heat, which stays warmer than winter air. NRCan estimates savings of about 10% to 20% more than a top cold-climate air-source unit sized for most of the load. Check the cost: the IRS FAQ says the separate 25D credit, which covered geothermal heat pumps, is not allowed for expenditures made after December 31, 2025, and an expenditure counts as made when the installation is finished.

Should I turn the heat pump down at night?

Only slightly. NRCan advises setbacks of no more than 2°C (about 3.6°F), or a smart thermostat that starts recovery early, because heat pumps respond more slowly than furnaces. In the PNNL field study, some auxiliary heat use was triggered by night setbacks or manual setpoint changes rather than by the cold itself.

Is the efficiency number on older brochures comparable?

Not directly. The NEEP specification lists 8.5 HSPF2 as equivalent to 10 HSPF and 7.7 HSPF2 as equivalent to 9 HSPF, so ratings under the older and newer test procedures should not be compared as raw numbers. Compare models on the same metric, and at 5°F where the data is published.

Questions to ask before you buy

1. What are your design temperature and the house's heat loss at that temperature, from a written load calculation?
2. What are the unit's capacity and COP at 5°F and at its lowest published temperature, and is it on the ENERGY STAR Cold Climate or NEEP list?
3. What backup is included, at what outdoor temperature can it start, and does it run during defrost?
4. What do your winter-month electricity and gas rates give for the break-even COP in the formula above?
5. Which state, utility or local rebates are open this month, and what do they require?

Sources

• PNNL-37127: Performance Results from DOE Cold Climate Heat Pump Challenge Field Validation (January 2025)
• Center for Energy and Environment: Cold Climate Air Source Heat Pump final report (Minnesota, 2017)
• Natural Resources Canada: Heating and cooling with a heat pump
• ENERGY STAR: Heat pump specification 6.2, revised February 2026
• NEEP: Cold Climate Air Source Heat Pump specification, version 4.0
• NEEP: ccASHP specification and product list
• Lennox: Emergency heat versus auxiliary heat
• EIA: British thermal units (Btu) conversion factors
• EIA: Electric Power Monthly, Table 5.3
• EIA: U.S. price of natural gas delivered to residential consumers
• IRS: FAQs on modification of 25C, 25D and other credits under Public Law 119-21
• IRS: Energy efficient home improvement credit (25C)
• U.S. Department of Energy: Home Energy Rebates Program