Why Is My Heat Pump Not Working?

By Mario Vaghei, General Manager, Aire One Peel Heating & Cooling · Published November 24, 2023 · Facts verified September 3, 2026

Heat pumps in cold weather are the most argued-about topic in Ontario home heating, and most of the argument runs on brochure numbers. This page runs on two others: the outdoor temperature Peel Region homes are actually designed for, and the efficiency a cold climate heat pump actually delivered when Natural Resources Canada measured one through an Ottawa winter. Put those side by side and the question mostly answers itself. If you are weighing the dollars rather than the physics, our heat pump versus furnace running cost page does that arithmetic; this one stays on what the cold does.

What happens to heat pumps in cold weather as the temperature drops?

A heat pump loses efficiency and capacity gradually as the outdoor air gets colder, and the two numbers that describe that slide are the coefficient of performance and the minimum operating temperature. The COP is how many units of heat the unit delivers per unit of electricity it uses. Electric baseboards score exactly 1.0. Anything above 1.0 is heat pulled from outdoor air for free, and a cold climate unit stays well above 1.0 in weather that would shut a conventional one down.

The best public Canadian measurement comes from Natural Resources Canada, which ran a cold climate air source heat pump through a heating season at its Canadian Centre for Housing Technology in Ottawa, with a 10 kW electric resistance backup. Heating COP ranged from an average of 3.0 at plus 4.9 degrees down to 1.5 at minus 21.1 degrees, and the system held comfort in the house at the coldest temperatures it saw, below minus 21, without leaning only on the resistance heater. Table 1 puts those measured points on the same ladder as the two temperatures that matter in Peel Region.

Table 1. The two COP figures are from a single NRCan field study on one cold climate unit in Ottawa, published September 2013, and NRCan did not publish readings at the intermediate temperatures, so none are invented here. Design temperature read from SB-1 for the Toronto area, applied to Mississauga and Brampton. Verified September 3, 2026.

How cold does it actually get in Peel Region?

Heating systems in the Toronto area are sized to an outdoor design temperature of minus 18 degrees Celsius, not to the coldest night anyone remembers. The Ontario Building Code, at Sentence 9.33.3.2, sends designers to MMAH Supplementary Standard SB-1, Climatic and Seismic Data, and tells them to use the 2.5 per cent design temperature criteria. That 2.5 per cent means the outdoor temperature is colder than the design value for roughly two and a half per cent of January hours, a handful of nights in a typical year.

That single number reframes the whole question about heat pumps in cold weather. A cold climate heat pump with a rated minimum of minus 25 is rated seven degrees past the line Mississauga and Brampton furnaces are already sized to. The nights that drop below minus 18 are the same nights a gas furnace is also running flat out; the difference is that the heat pump may need its backup for a few hours while the furnace simply burns more gas. Neither system is oversized for the average January day, and neither should be.

What takes over when the heat pump cannot keep up?

A backup heat source is part of every Ontario design for heat pumps in cold weather, and the choice between electric resistance and a gas furnace is the biggest decision on the quote. Electric resistance is a heating coil in the air handler; it is simple, it is always there, and it costs the same per unit of heat as a baseboard. A dual fuel system keeps or adds a gas furnace and lets the thermostat hand over to it below a set outdoor temperature. Table 2 sets out the mechanics, not the running cost, which lives on the running cost page.

Table 2. As of September 3, 2026. The balance point on a dual fuel system is set at commissioning and can be moved; ask for it in writing.

What should the spec sheet say for an Ontario winter?

Four lines on a specification sheet decide how heat pumps in cold weather actually behave through a Peel Region winter, and none of them is the SEER rating the summer advertising leads with. Table 3 lists them with the floor Canada sets and what to look for beyond it. Bring this to the quote; a contractor who cannot point to each line on the manufacturer’s sheet for the exact model number is quoting from memory.

Table 3. Canadian floors from the NRCan heat pump guide; rebate condition from the Home Renovation Savings Program page. Verified September 3, 2026. Equipment figures for any specific model come only from that model’s own manufacturer sheet.

Why does it blow steam and ice up in January?

Frost on the outdoor coil and a cloud of steam every hour or so are normal behaviour for heat pumps in cold weather, not faults. Pulling heat from air near freezing chills the coil below the dew point, moisture freezes onto it, and the unit periodically reverses for a few minutes to melt it off. During that defrost the indoor fan may pause or the backup strips may run, which is the brief cool draft some homeowners notice. It is designed in.

What is not normal is a coil encased in solid ice for hours, an outdoor unit sitting in a snowdrift with no airflow, or a system that never comes out of defrost. Those are service calls, and the free checks before you make one are on our heat pump not working page. Keeping the outdoor unit clear of snow and off the ground on a stand is the one cold-weather task that is genuinely yours.

Does Ontario pay for a cold climate heat pump?

Yes: the Home Renovation Savings Program, delivered by Save on Energy and Enbridge Gas, currently offers up to $7,500 CAD for a cold climate air source heat pump, on condition that the model is on Natural Resources Canada’s qualified products list. Table 4 gives the heat pump lines only; the full programme, the after-rebate arithmetic and typical install prices are on our cost to install a heat pump in Ontario page.

Table 4. Home Renovation Savings Program, amounts read from the programme page on September 3, 2026. Amounts and eligibility change; confirm on the programme site before you commit. The Canada Greener Homes Grant closed in February 2024 and is not available; its separate loan and the Oil to Heat Pump Affordability stream are different programmes.

Which electricity utility do you call in your city?

Once a heat pump is your main heat, your electricity price plan matters far more than it did with a gas furnace, and the plan is changed through your local distributor, not through the Ontario Energy Board. The rates themselves are provincial and reset every November 1, so they are kept on the running cost page rather than repeated here. The distributor is city-specific, and Table 5 is the list.

Table 5. Distributor by municipality as of September 3, 2026. A few streets on municipal boundaries are served by a neighbouring distributor; your bill names the right one.

Which setup fits your house?

Two questions, and it points at the backup arrangement that suits your home, using the same logic as Table 2.

Rebate eligibility is decided by the programme, not by us. The right size for your house comes from a heat loss calculation, not from this finder.

Frequently asked questions

Do heat pumps work in cold weather?

Yes, if the unit is a cold climate model. Natural Resources Canada measured a cold climate air source heat pump in Ottawa delivering heat at a COP of 1.5 at minus 21.1 degrees Celsius, meaning it still produced one and a half units of heat per unit of electricity. Conventional heat pumps built for milder climates lose capacity much earlier, which is where the old reputation comes from.

At what temperature does a heat pump stop working?

Each model has a rated minimum operating temperature, and NRCan puts that between minus 15 and minus 25 degrees Celsius for newer units. Below its rated minimum the unit shuts down or its output falls short, and the backup carries the house. It is a design line on the spec sheet, not a surprise, so ask for it for the exact model number before you sign.

Do heat pumps work at minus 20 in Ontario?

A cold climate heat pump does. The Toronto area, including Mississauga and Brampton, is designed to minus 18 under MMAH Supplementary Standard SB-1, and a unit rated to minus 25 has margin past that. NRCan’s Ottawa field data at minus 21.1 showed the house holding comfort with the heat pump still doing most of the work. Below the rated minimum, backup heat takes over as intended.

Is a heat pump worth it in Ontario winters?

Physically, yes: cold climate heat pumps in cold weather cover a Peel Region winter with a backup for the few nights below its rated minimum. Financially, the answer depends on whether your backup is gas or electric and which electricity plan you are on, which is a separate calculation. The Home Renovation Savings Program currently offers up to $7,500 CAD toward a qualifying cold climate unit, which changes that calculation for most homes.

Why is my heat pump blowing steam or icing up in winter?

Frost on the outdoor coil and periodic clouds of steam are normal defrost cycles. The coil runs colder than the outdoor air, moisture freezes onto it, and the unit reverses for a few minutes to melt it off. A coil sealed in solid ice for hours, a unit buried in snow, or a system that never leaves defrost is different, and those are the cases worth a service call.

Do I still need a furnace with a heat pump in Ontario?

You need a backup heat source, and a furnace is one of the two common choices. In a dual fuel system the existing gas furnace stays and takes over below a set outdoor temperature. In an all-electric system, resistance strips in the air handler do the same job. Either way the backup is part of the design, and a quote that has no backup at all is incomplete for a Peel Region home.

Final verdict

Heat pumps in cold weather are a settled question for the cold climate type: the Toronto area is designed to minus 18, NRCan measured a unit still delivering a COP of 1.5 at minus 21, and the units on the market are rated to minus 25. The remaining decision is the backup, gas or electric, and that is a question about your house and your bill, not about whether the technology works.

Where we are not the best answer: if your home is on a thin-insulation, draughty envelope, the assessment rebate and the insulation lines on the same programme will do more for January than any equipment change, and an insulation contractor is who you need first. We would rather tell you that than size a heat pump to a house that leaks.

Sources and references

• Cooling and Heating Season Performance Assessment of a Cold Climate Air Source Heat Pump at the Canadian Centre for Housing Technology, Natural Resources Canada, September 2013. COP figures in Table 1.
• Heating and Cooling With a Heat Pump, Natural Resources Canada. Minimum operating temperature range and Canadian HSPF floor, read September 3, 2026.
• Ontario Building Code, O. Reg. 332/12, Sentence 9.33.3.2, outdoor design temperatures, referencing MMAH Supplementary Standard SB-1, Climatic and Seismic Data.
• Home Renovation Savings Program, Save on Energy and Enbridge Gas. Table 4 amounts read September 3, 2026.
• O. Reg. 463/10, Ozone Depleting Substances and Other Halocarbons, Government of Ontario. Refrigerant handling requirements.
• Technical Standards and Safety Authority, the Ontario authority for fuels safety and gas technician certification.

Mario Vaghei

General Manager, Aire One Peel Heating & Cooling

Mario pulled the two COP figures on this page from the NRCan field study itself rather than from any summary of it, and chose to publish no brand performance percentage because none could be tied to a public capacity table. He is General Manager, not a licensed trade, so the refrigerant, electrical and gas guidance here stops where a certified technician’s work begins.