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Cold-Climate Air-Source Heat Pumps in Ontario: What Works at Minus 25, What Does Not
Heating and efficiency Heat pumps From a builder
Cold-Climate Air-Source Heat Pumps in Ontario: What Works at Minus 25, What Does Not
Ten years ago an air-source heat pump in Simcoe County was a summer appliance with a gas furnace doing the real work. The cold-climate units changed that. Here is what they do at the temperatures we actually get, and what has to be true for one to carry a house.
Short version: A cold-climate air-source heat pump (cc-ASHP) keeps heating down to about minus 25 to minus 30 degrees C, with its output and efficiency dropping as it gets colder. It carries a well-insulated house on its own for most of an Ontario winter and needs backup heat (electric strips, a gas furnace or a boiler) for the coldest nights unless it is oversized for them. Size it from a CSA F280 heat loss of the actual house, not the square footage. In an ICF house the heat loss is small enough that a modest unit does the job; in a leaky house the heat pump just runs the backup.
What makes a heat pump cold-climate
A standard air-source heat pump loses most of its capacity below freezing and shuts off around minus 10 to minus 15. A cold-climate unit uses a variable-speed inverter compressor and a different refrigerant circuit to keep pulling heat from outdoor air down to minus 25 or lower, and it is rated for it: look for the capacity at minus 15 and minus 25, not just the nameplate at plus 8. NRCan’s heat pump guidance explains the ratings, and the rebate programs publish lists of qualifying models.
The physics still apply. At minus 25 the unit delivers maybe half to two thirds of its capacity at plus 8, and its efficiency (coefficient of performance) drops from around 3 to somewhere near 1.5 to 2. It is still making more heat than an electric baseboard would from the same electricity; it is just making less of it than on a mild day.
Can it carry the house?
That depends entirely on the heat loss. A house that loses 60,000 BTU per hour at the design temperature needs a lot of heat pump and a lot of backup; a house that loses 25,000 needs a small unit and barely touches the backup. The heat loss comes from the envelope, which is why the heat pump conversation is really an insulation conversation. Do I need a heat loss calculation explains the CSA F280 number every heating design should start from, and the heat loss calculator gives a first estimate.
In our ICF houses, with triple-pane windows and an HRV, a cold-climate heat pump sized to the design heat loss carries the house through all but a handful of nights a year, and the backup is a small electric element or a boiler that was going to be there for the radiant floors anyway. In a 1980s house with R-12 walls, the same unit runs the backup from December to March and the owner wonders what the fuss was about.
Backup heat: three ways
| Backup | How it works | When it makes sense |
|---|---|---|
| Electric resistance | Strip heaters in the air handler or baseboards; cheap to install, expensive to run | Tight, well-insulated houses where backup runs a few days a year |
| Dual fuel with gas | A gas furnace takes over below a switchover temperature | Houses with gas already, leaky houses, anyone nervous about hydro bills on the coldest nights |
| Hydronic boiler | An air-to-water heat pump feeds radiant floors with a boiler as backup | Radiant houses; our usual design on ICF homes |
Whatever the backup, the controls decide the bill: a switchover temperature set too high runs the backup when the heat pump could still do the job cheaper. Ask the installer to show you the balance point calculation. Gas vs heat pump operating cost puts numbers on the switchover.
Ducted, ductless, or air-to-water
- Ducted (central): a single outdoor unit and an indoor air handler on the duct system. The normal choice for a new house with forced air; one thermostat, filtered air, cooling included.
- Ductless (mini-split): one or more wall or floor heads. Excellent for additions, cottages and open plans; awkward in a house with many small rooms. Each head is a visible box on a wall.
- Air-to-water: the outdoor unit heats water for radiant floors or fan coils. Pairs with ICF and radiant the way we build; cooling needs fan coils or a separate system. Radiant heat vs forced air covers the comfort side.
Installation details that decide whether it works
- Sizing from the F280 heat loss at the design temperature for your location, not from square footage or from the old furnace.
- Outdoor unit placement: off the ground on a stand above the snow line, out of the roof drip line, with room for the defrost water to drain and not become an ice rink on the walkway.
- A sound check: inverter units are quiet, but not silent, and the bedroom window above the unit will tell you.
- Electrical: a 200 amp service is usually needed; see 100 vs 200 amp service.
- Controls commissioned and the balance point set, with the owner shown how it works.
- An HRV, because a tight house with a heat pump needs the fresh air designed, not leaked.
Rebates and cost
The Home Renovation Savings Program and utility programs have offered meaningful rebates on qualifying cold-climate heat pumps for existing homes; new construction programs change often, so check the current program and our guide to it before you count on anything. Installed cost depends on the type and the backup; the geothermal and radiant cost pages on this site give the comparison points. On operating cost, a cold-climate heat pump in a tight house beats electric resistance by a wide margin and competes with natural gas depending on the rates and the winter; the next page runs the numbers.
Related guides on this site
Sources and further reading
Questions people ask
Does an air-source heat pump work at minus 30 in Ontario?
A cold-climate model keeps producing heat down to about minus 25 to minus 30, at reduced capacity and efficiency. Most houses need some backup heat for the coldest nights unless the unit is oversized for them, which costs efficiency the rest of the year.
Do I need a furnace as backup for a heat pump?
You need some backup unless the house is very tight and the unit is sized for the design temperature. Backup can be electric strips, a gas furnace in a dual-fuel setup, or a boiler in a radiant system. The heat loss calculation decides how much.
How do I size a heat pump for my house?
From a CSA F280 heat loss of the actual house at your location's design temperature. Square-footage rules of thumb oversize leaky houses and undersize nothing; they just miss.
Is a heat pump cheaper than gas to run in Ontario?
In a well-insulated house, often comparable or cheaper for most of the winter, with the coldest weeks depending on the rates. In a leaky house the heat pump runs its backup and the savings disappear. The envelope decides.
Size it from a heat loss, not a guess
Every heating choice starts with the heat loss of your actual house. OntarioHeatLoss.ca produces the CSA F280 calculation and the mechanical design your permit needs, anywhere in Ontario.
Reviewed and updated October 2026. Costs are Ontario ranges, not quotes; code references are to the Ontario Building Code in force at that date.
