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Cold Climate Heat Pumps

What makes a heat pump cold-climate?

Standard heat pumps lose output fast as outdoor temperatures drop, because the refrigerant has less heat to pull from colder air. Cold-climate designs use variable-speed (inverter) compressors that can speed up in the cold, enhanced vapour injection or similar refrigerant circuits, larger outdoor coils and better defrost controls. The result is that output at 5°F can be close to the rating at 47°F. Some programs publish lists of products that meet cold-climate performance criteria, such as a minimum COP and capacity ratio at 5°F. Check whether your utility or incentive program uses such a list.

Reading capacity at low temperatures

Look at the extended performance table. It lists maximum, rated and minimum output and power draw at several outdoor temperatures. Divide output at 5°F by output at 47°F to get a capacity retention ratio; units marketed for cold climates often hold 70 to 100 percent. Then compare the 5°F output with your home's heat loss at your design temperature. If your design low is −10°F, look for data at that point too.

COP in cold weather

Efficiency falls as it gets colder. A cold-climate unit might have a COP around 3 to 4 at 47°F and around 1.8 to 2.5 at 5°F. Even at a COP of 1.8 it still delivers 1.8 units of heat per unit of electricity, better than resistance heat at 1.0. Read COP explained for how this affects bills.

Sizing strategy

In cold regions contractors usually size to cover the heat loss at or near the design temperature, so backup heat runs only during rare extremes. Some homeowners choose a slightly larger variable-speed unit to reduce backup use; because inverters modulate down, mild oversizing is less of a problem than with single-stage units. Others keep an existing furnace as backup in a dual-fuel system. Start with the heat pump size calculator and discuss options with your contractor.

Installation details that matter in the cold

• Mount the outdoor unit on a stand or wall bracket above typical snow depth.
• Keep it out from under roof drip lines; ice can block the coil.
• Allow clear drainage for defrost meltwater so ice does not build up beneath.
• Choose a location that limits wind-driven snow into the coil.
• Insulate line sets and seal wall penetrations to prevent drafts.

Backup heat options

Options include electric resistance strips in the air handler, an existing gas or oil furnace, baseboard heaters or a wood stove. Electric strips are simple but costly to run and add electrical load. See backup heat strips and heat pump vs furnace.

Defrost in cold climates

In humid cold weather between about 20 and 40°F, frost builds quickly and defrost runs more often. Brief interruptions are normal. See heat pump defrost mode.

Worked example

Figures below are illustrative examples (2026-10-29), not quotes or guarantees.

A house with a design heat loss of 32,000 BTU/h at −5°F considers two 3-ton units. Unit A delivers 34,000 BTU/h at 5°F and 28,000 at −5°F. Unit B delivers 24,000 at 5°F and 17,000 at −5°F. On a design day Unit A needs about 4,000 BTU/h of backup and Unit B about 15,000 BTU/h, or roughly 4.4 kW of resistance heat. At $0.15/kWh, an hour of that backup costs about $0.66 with Unit B versus about $0.18 with Unit A.

Common myths

"Heat pumps do not work below freezing." Modern cold-climate units do. "You must keep a furnace." Many homes in cold regions heat entirely with heat pumps plus small electric backup. "Higher tonnage is safer." Oversized single-stage units can short-cycle; size from a load calculation.

Reading the low-temperature table

Cold-climate units publish extended performance tables showing capacity and COP at several outdoor temperatures. Look for the maximum output at 5°F and, if listed, at −5°F or −13°F. A unit that keeps 80 to 100 percent of its rated capacity at 5°F will usually need less backup than one that falls to 60 percent. Use the maximum column for sizing, not the rated or nominal column, because the rated point is often set at a mild temperature.

Design temperature and your location

Your local heating design temperature is the outdoor temperature that is colder than about 99 percent of winter hours. Contractors take it from published tables for your city. Matching the heat pump's output at that temperature to the house's heat loss at that temperature is the core of cold-climate sizing. If the unit falls short at the design point, the difference is covered by backup heat or a second system, and that shortfall should be stated on the quote.

Installation details that matter in the cold

Outdoor units in snowy regions need a stand or wall bracket that lifts them above typical snow depth, clear airflow on all sides, and a defrost drain path that will not freeze into an ice dam under the coil. Avoid placing the unit under a roof edge that drips. Line sets should be insulated and sealed where they pass through the wall. These items rarely appear in brochures but have a large effect on winter reliability.

Living with a cold-climate system

Expect longer run times and lower supply-air temperatures than a furnace. Air from the registers may feel lukewarm even though the house is holding temperature. That is normal for a variable-speed heat pump running steadily. Keep setpoints steady, keep the outdoor unit clear of snow and ice, and check filters monthly during the first winter.

FAQ

What is a good capacity ratio at 5°F?

Many cold-climate units hold 70 percent or more; compare with your load.

Will my bills go up in a cold snap?

Yes, because efficiency falls and backup may run, but snaps are short.

Do cold-climate units cool well too?

Yes, they are full heat pumps; check SEER2.

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