Quick answer
A cold-climate heat pump keeps producing heat through any normal Burlington winter. Most cold-climate models are rated to operate down to about -25°C to -30°C and still deliver most of their rated capacity at -15°C; below the rated minimum some units lock out and others lose output. A standard (non-cold-climate) heat pump fades below about -5°C to -10°C and needs backup heat long before it stops running.
A cold-climate unit keeps working to about -25°C to -30°C and a standard unit needs backup below about -5°C to -10°C, so at what temperature a heat pump stops working depends first on which class you own. Homeowners picture an older unit giving up at the freezing mark; that was roughly true of heat pumps sold 20 years ago. The other two variables are how the unit was sized and where your house sits between Lake Ontario and the escarpment.
Cold-climate heat pumps keep running to about -25°C to -30°C
A cold-climate air-source heat pump is designed and tested for exactly this question. Manufacturers such as Mitsubishi and Daikin publish a minimum operating temperature, typically somewhere between -25°C and -30°C, below which they no longer guarantee operation — some units lock the compressor out for protection at that point, others keep running with reduced output. Either way it is colder than the lakeshore sees in a normal winter; only a rare polar-vortex night comes close.
Capacity is a more useful number than the shutdown point. A cold-climate unit is rated to deliver most of its heating output at -15°C, and the manufacturer's capacity table shows the exact figure. That -15°C line is also what rebate programs look at when they list eligible models; the Ontario rebate guide explains which listings the current program accepts.
Standard heat pumps fade below about -5°C to -10°C
A standard-efficiency heat pump — the kind sold as an air conditioner with a heating mode — still runs below freezing, but its output drops steeply and its efficiency falls with it. Somewhere around -5°C to -10°C it can no longer cover a typical house on its own, so the thermostat brings on backup heat. The compressor has not failed; it cannot pull enough heat out of the air at that point to keep up.
How to read a spec sheet for cold weather
- Minimum operating temperature: the coldest point at which the manufacturer guarantees the unit will run. Anything at -25°C or below is comfortably beyond a normal Halton winter.
- Rated heating capacity at 8.3°C, -8.3°C and -15°C: the three standard rating points. Compare the -15°C number to your house's heat loss, not the headline capacity at 8.3°C.
- Coefficient of performance (COP) at -15°C: how many units of heat you get per unit of electricity on a cold day. The widely used NEEP cold-climate specification requires at least 1.75 at that temperature, against exactly 1.0 for electric baseboards or backup strips.
- Backup heat type and lockout: whether the unit is paired with electric strips or a gas furnace, and the temperature at which the thermostat hands over.
Your balance point matters more than the shutdown temperature
The balance point is the outdoor temperature at which the heat pump's output exactly equals the heat your house loses. Above it the heat pump carries everything; below it, backup heat makes up the difference. As an illustration only, a tight 2000s build in Alton Village might have a balance point near -12°C, while a 1950s Aldershot bungalow with original single-pane windows could sit near -3°C with identical equipment.
Sizing sets the balance point, and sizing is where disappointing heat pump installs usually went wrong. Settle what size heat pump you need before worrying about the coldest night of the year.
What Burlington winters actually throw at a heat pump
- Lakeshore neighbourhoods such as Roseland, Aldershot and Bronte are moderated by Lake Ontario and only occasionally dip past -20°C.
- Above the escarpment — Waterdown, the Hamilton Mountain, Binbrook — nights run a few degrees colder and windier; wind raises heat loss, which raises the balance point and adds hours below it.
- The Ontario Building Code's January design temperature for Burlington, Oakville and Hamilton sits in the high minus teens. That figure, not the record low, is what a heat-loss calculation sizes to.
- Damp air off the lake between about -7°C and 5°C frosts the outdoor coil faster than dry cold does, so a heat pump spends more time in defrost on a grey January day than on a clear -15°C morning.
- The handful of nights each winter near -20°C are where backup heat earns its keep, whether that backup is a gas furnace or electric strips.
What to expect on the coldest nights
Expect the outdoor unit to run almost continuously, expect the supply air to feel cooler than a furnace's, and expect the backup stage to come on for part of the night. All three are normal behaviour for a cold-climate system. What is not normal is a house losing temperature while the outdoor unit runs; that points to a charge, defrost or thermostat problem, and why does my heat pump run constantly walks through the difference.
Whether to switch the heat pump off entirely during a cold snap is a separate question with a different answer — see should I turn off my heat pump in extreme cold. The short version: leave it running and let the thermostat manage the handoff.
ZK Mechanical sizes and installs cold-climate heat pumps from our shop on North Service Road, and we can tell you your house's balance point before you commit to equipment. See heat pump installation in Burlington or ask for a free in-home assessment.