How a Cold-Climate Heat Pump Actually Performs Below −15°C in Canada
The question is rarely whether a cold-climate heat pump works at −15°C. It does. The useful questions are narrower: how much heat can it still deliver at that temperature, at what efficiency, and at what outdoor temperature does your backup heat genuinely need to start helping? Those three answers are printed — or pointedly not printed — on every quote you will ever be handed. This guide shows how to read them before signing anything.
What changes below −15°C: capacity and COP fall together
A heat pump moves heat rather than making it, and its efficiency is expressed as a coefficient of performance (COP): a COP of 3 means three units of heat delivered for every unit of electricity consumed. Electric resistance heat — baseboards or an auxiliary strip — has a COP of exactly 1.0. That is the floor every comparison in this article is measured against.
Two things happen as the outdoor temperature drops. The home loses heat faster, so it needs more. At the same time the heat pump can extract less heat from colder air, so it delivers less, and works harder for each unit it does deliver. Published vendor bands for a high-performance cold-climate system illustrate the shape of the curve: a COP of roughly 3 to 4 or more between +5°C and −5°C, typically 2 to 3 between −5°C and −15°C, and about 1.5 to 2 between −15°C and −25°C, with supplemental heat needed below the balance point. Treat those bands as a map of the terrain, not a promise about a specific model — the model-specific numbers come from the verification step below.
One warning about language. Any claim that a heat pump holds “100% efficiency” down to some temperature is mixing up two different ideas: capacity maintenance (how much of its rated output it still delivers) and COP (how efficiently it delivers it). A unit can hold most of its capacity while its COP quietly falls. Ask which number is being quoted.
The three numbers that define “cold-climate” in Canada
Canada has an actual definition to lean on. The criteria Natural Resources Canada applied for the Canada Greener Homes cold-climate air-source heat pump list were three testable thresholds, plus a seasonal efficiency floor:
| Check | Cold-climate threshold | Why it matters |
|---|---|---|
| COP at −15°C, maximum capacity | At least 1.8 | At the temperature this article is about, the unit still delivers 1.8 units of heat per unit of electricity — 80% more heat than resistance backup for the same electricity. |
| Capacity maintenance | At least 70% (output at −15°C ÷ rated output at 8.3°C) | A unit that keeps only half its rated capacity needs its backup far more often than the headline size suggests. |
| Compressor | Variable capacity: 3+ speeds or continuously variable | Modulation is what lets the unit match a falling load instead of cycling on and off. |
| Seasonal efficiency | HSPF2 (Region V) at least 6.6 and SEER2 at least 15.2 | The whole-season picture, so a unit cannot pass on one cold-day number alone. |
That table is the spec-verification step: take any quote, find those three cold numbers in the manufacturer's published data or the eligible-product listing, and confirm each one. If a salesperson cannot point to the COP at −15°C and the capacity maintenance figure, the phrase “cold-climate” on the brochure is doing marketing work, not engineering work. Cold-climate equipment also carries a published heating capacity rating at −15°C or below; standard heat pumps are typically rated only to −8°C or 0°C, which means their output at −15°C is simply untested — not necessarily bad, but unknown, and unknown is a poor basis for a Canadian January decision.
A timing note: the Canada Greener Homes Grant has closed (December 31, 2025 was the last day to submit documents), so these criteria are used here purely as a performance benchmark. Check the site's rebates guide for what programs are current before counting on any incentive.
Rated versus measured: what field monitoring found
Ratings are laboratory numbers. Monitored homes tell a reassuringly similar story. A review of field studies recorded in-field testing in a well-insulated Ontario house where COP was about 1.8 at the lowest outside temperature reached, −19°C, rose to about 5.0 at 9°C, and averaged about 2.75 across the −10°C to 0°C range. In other words, at a temperature four degrees below the −15°C line, the measured machine was still delivering roughly 1.8 times the heat of resistance heating for the same electricity — right at the Canadian cold-climate threshold, in a real house, not a lab. Field testing in Connecticut found COP above 2.5 below freezing and about 2.3 at a daily average of −15°C, and across the reviewed datasets the median COP on the coldest monitored day was 2.4.
The honest reading cuts both ways. Efficiency at deep cold is real but modest: nobody's heat pump is a COP-4 machine at −20°C. And the Ontario result came from a well-insulated house — envelope first still applies, because a leaky house raises the load line the heat pump has to meet (see where your home loses heat).
Thermal balance point versus economic balance point
The balance point is the outdoor temperature at which the heat pump's output exactly matches the home's heat loss; below it, supplemental heat is required to hold the setpoint. That is the thermal balance point, and it is a property of the house-and-machine pairing, not of the machine alone.
Natural Resources Canada's sizing and selection guide lays out four sizing strategies, from an emphasis on cooling through to sizing the heat pump as the principal heating source, and the design balance point moves dramatically with the choice — from above freezing for cooling-emphasis sizing down to at or below the design temperature when the heat pump is sized to carry the heating load. A Manitoba utility summary of the same framework notes that a heating-emphasis sizing can carry the full load down to about −8°C, after which electric resistance heat is also required even though the heat pump itself can keep running. Sizing starts with a real heat-loss calculation — CSA F280 is the standard method, and an EnerGuide report can supply the loads.
The economic balance point is a different dial, and it only exists on dual-fuel systems paired with a gas furnace. It asks: below what temperature is the furnace the cheaper heat source per unit of heat, given local gas and electricity prices? With electric resistance backup there is no economic case for switching early — resistance heat at COP 1.0 never beats a heat pump still running at COP 1.8 — so the heat pump should be allowed to run as long as it can hold the house, with the strips topping up only the shortfall. With gas, the crossover is a prices question that changes when rates change, and it should be set deliberately, not left at whatever default the installer used.
Setting auxiliary heat so it helps instead of taking over
Most disappointment with cold-climate systems is a controls problem, not a machine problem. Three habits do most of the damage: a large overnight setback that triggers full auxiliary heat on morning recovery (the site's auxiliary heat guide covers this in depth), an auxiliary lockout temperature set far too warm “to be safe,” which hands ordinary cold days to the most expensive heat source in the house, and judging the system by its worst hour instead of its season. Use small setbacks or smart recovery, set the aux lockout at or near the thermal balance point from the sizing calculation, and let the heat pump run long and steady — variable-capacity machines are built to modulate, with enhanced vapour injection specifically boosting capacity and COP at −10°C and below.
A pre-winter decision checklist
- Verify the quote: COP at −15°C at least 1.8, capacity maintenance at least 70%, variable capacity — all three, in published data.
- Confirm the sizing basis: a CSA F280 or EnerGuide heat-loss calculation, and which NRCan sizing strategy (cooling emphasis through principal heating) the quote follows.
- Ask for the balance point: the calculated thermal balance point for your house, in writing, and the auxiliary lockout set to match it.
- For dual-fuel: ask how the economic switchover temperature was chosen and what prices it assumes.
- Plan the envelope: insulation and air-sealing lower the load line and the balance point with it — the cheapest capacity is heat the house never loses.
What success looks like: on a −18°C night, the heat pump runs long, steady cycles, the auxiliary indicator comes on only briefly or not at all, and the indoor temperature holds at the setpoint. That is the system working exactly as the numbers said it would.
FAQ
Does a heat pump stop working at −15°C? A cold-climate unit does not. By the Canadian listing definition it is still delivering at least 70% of its rated capacity and a COP of at least 1.8 at −15°C, and monitored Ontario equipment measured a COP of about 1.8 at −19°C.
Is it cheaper to switch to backup below −15°C? With electric resistance backup, no: at COP 1.8 the heat pump is still the cheaper source, and the backup should only top up. With a gas furnace, the answer depends on local prices — that is the economic balance point, and it is a setting to revisit when rates change.
Why does the backup come on during morning warm-up? Recovery from a deep setback demands heat faster than the heat pump alone can supply it, so the controls call the auxiliary. Smaller setbacks or smart recovery avoid most of it.
General information only, not equipment advice for a specific home. Sizing, refrigerant and electrical work belong to licensed contractors, and program rules change — verify incentives against current official sources before buying.