Key takeaways
- Toronto’s coldest month averages around −4 °C to −6 °C — well inside a cold-climate heat pump’s comfort zone.
- Efficiency drops as it gets colder, but a good unit still delivers roughly 1.5–2× the heat of electric baseboards at −20 °C.
- Look for “cold-climate” (ccASHP) models and check their rated output at −15 °C and below, not just at mild temperatures.
- Plan backup heat for the few hours a year below your system’s balance point.
What a Toronto winter really asks of your system
Most heating hours in Toronto aren’t extreme. January typically averages around −4 °C to −6 °C, and nights below −20 °C are uncommon — a handful of hours in most winters. That matters because a heat pump works hardest (and least efficiently) only in those rare extremes.
Installers size heating equipment to a “design temperature” — a cold outdoor temperature your home should stay comfortable at. For Toronto it’s around −18 °C to −20 °C. Ask your installer which value they used.
Efficiency vs. outdoor temperature
The colder it is, the harder the heat pump has to work to pull heat from the air, so its COP falls. But even at its lowest, a cold-climate unit is still more efficient than electric resistance heat (COP 1) — and far above it on most days.
The curve above is illustrative. Every model has its own published performance data — ask for the capacity and COP at −15 °C and at your design temperature.
Reading cold-climate ratings
| Rating | What it tells you | What to look for |
|---|---|---|
| Cold-climate (ccASHP) listing | The model meets a cold-climate performance specification. | Listed as cold-climate; for rebates, on the NRCan qualified products list. |
| Capacity at −15 °C | How much heat (BTU/h) it can still deliver when it’s cold. | Close to its rated capacity at 8 °C — a small drop is a good sign. |
| COP at −15 °C | Efficiency when it’s cold. | About 1.75 or higher is a common cold-climate benchmark. |
| HSPF2 | Seasonal heating efficiency. | Higher is better; compare models using the same region rating. |
| SEER2 | Seasonal cooling efficiency. | Higher is better — matters for summer bills. |
Defrost cycles: the steam is normal
In cold, humid weather, frost forms on the outdoor coil. The unit periodically reverses for a few minutes to melt it. You might see steam and hear a “whoosh” — both are normal. Good installations make defrost a non-event:
- Raise the outdoor unit on a stand or wall bracket above typical snow depth
- Keep meltwater draining away — not onto walkways where it can freeze
- Avoid placing it under a roof drip line
- Keep 30–60 cm clear around the unit and brush off heavy snow
Staying comfortable on the coldest nights
- 1Size to your heat lossA room-by-room heat-loss calculation sets the target output at design temperature. See our sizing guide.
- 2Choose the backupElectric strips, your existing furnace (hybrid) or your current boiler. Decide before you buy.
- 3Set the switch-overYour installer programs when backup heat engages — usually an outdoor temperature or a “can’t keep up” signal.
- 4Leave the thermostat steadyDeep night setbacks make the system recover in the cold, which is when backup heat runs. Small setbacks work better.
Reducing drafts and adding attic insulation lowers your heat loss, which can mean a smaller heat pump, less backup heat and lower bills.
Common questions
Will my house feel as warm as with a furnace?
A furnace blows short bursts of very hot air. A heat pump delivers slightly cooler air more continuously. Rooms stay at a steady temperature, but air at the vent may feel less hot. Most people notice fewer temperature swings.
What if the power goes out?
Like a modern furnace, a heat pump needs electricity to run. If outages concern you, ask about a backup generator or keeping a non-electric backup.
Does snow damage the outdoor unit?
No — units are built for outdoor winters. The key is placement: raised above snow, clear of roof drips, with room to drain meltwater.