Cold-Climate Heat Pumps: How They Handle Ontario Winters

The most common question we hear about heat pumps in Ontario is simple: will it keep my house warm in January? For a properly chosen cold-climate model, sized and installed for your home, the answer is yes. But a heat pump behaves differently from a furnace in the cold, and knowing how helps you buy the right equipment and set realistic expectations.

What makes a heat pump "cold-climate"

Older heat pumps lost most of their output below about −5 °C to −10 °C. Today's cold-climate air-source heat pumps (ccASHP) use variable-speed (inverter) compressors, enhanced vapour injection or similar technology, and larger coils to keep working down to roughly −25 °C to −30 °C.

There is no single legal definition used on every product, so check the details yourself:

Capacity at low temperature. The manufacturer should publish heating output at −15 °C (5 °F) and ideally at −25 °C. A good cold-climate unit keeps most of its rated capacity at −15 °C.
Low-temperature COP. Coefficient of performance (COP) is heat out divided by electricity in. Above 1.0 means the heat pump is still beating electric resistance heat.
HSPF2 for Region V. The HSPF2 rating used since 2023 is based on a moderate climate (Region IV). Region V figures better reflect Ontario conditions and are lower.
Qualified-product listing. To get a Home Renovation Savings rebate, the model must be on the program's qualified-products list. Confirm on https://saveonenergy.ca (opens in a new tab).

How performance changes with temperature

The table below shows typical behaviour for a good ducted cold-climate unit. These are illustrative estimates, not figures for any specific model.

Outdoor temperature	Typical COP (estimate)	Share of rated capacity (estimate)	What it feels like indoors
+8 °C	3.5–4.5	100%+	Runs at low speed, very quiet
−8 °C	2.5–3.0	85–100%	Runs longer, steady comfort
−15 °C	2.0–2.5	70–90%	Long run times, defrost cycles more frequent
−25 °C	1.5–2.0	50–75%	Backup heat may run to keep up
Below −30 °C	~1.0 or shut off	Low or none	Backup heat carries the load

Because most of the heating season is milder than −10 °C, the average seasonal COP in Southern Ontario is typically around 2.5–3.0. In Ottawa and the north it is lower, because more hours fall in the colder bands.

How cold does it actually get?

Climate matters more than the brand. Heating degree days (HDD) measure how much heating a location needs over a year.

Region	Approx. heating degree days	Design temperature range (approx.)	Practical approach
Toronto, Hamilton, Niagara, Windsor, London	3,500–4,000 (Toronto ~3,500–3,600)	about −18 °C to −22 °C	ccASHP can usually carry the full load with modest backup
Ottawa, Kingston, Eastern Ontario	~4,500	about −25 °C	Size closer to design load; reliable backup recommended
Sudbury, North Bay, Thunder Bay	~5,000–5,700	about −28 °C to −33 °C	Hybrid with gas or propane, or generous electric backup

Design temperatures are approximate; your contractor should use the Ontario Building Code climatic values for your municipality.

Backup heat: what it is and when it runs

Almost every Ontario heat pump install has some form of backup or supplementary heat. The two main options:

Electric resistance strips inside the air handler. Simple and low cost to install, but they run at COP 1.0, so they are expensive to operate. They also need a large electrical circuit.
An existing or new furnace (gas, propane or oil) in a hybrid or dual-fuel setup. The thermostat switches to the furnace below a set outdoor temperature. See our hybrid heating guide.

Caution: A heat pump sized too small, or a thermostat programmed with deep night setbacks, can cause electric backup strips to run far more than needed. That is the most common reason for an unexpectedly high winter hydro bill.

Good practice for controls:

Set an outdoor lockout temperature for electric strips so they only run below, say, −15 °C to −20 °C or during defrost.
Keep setbacks small (1–2 °C) or turn them off. Heat pumps recover slowly, and a large morning recovery can trigger backup heat. Our smart thermostat guide explains the settings.
Use a thermostat designed for variable-speed heat pumps, ideally the manufacturer's communicating control.

Defrost, snow and ice

When the outdoor coil is below freezing in humid weather, frost builds up. The unit periodically reverses for a few minutes to melt it. You may see steam rising from the outdoor unit and hear a whoosh; that is normal. Defrost water has to go somewhere, and in Ontario it can freeze into a block of ice if drainage is poor.

Outdoor unit checklist:

Mounted on a stand or wall bracket that keeps the base at least 30–45 cm (12–18 in.) above typical snow depth; more in snowbelt areas east of Lake Huron and Georgian Bay.
Not under a roof edge without eavestroughs, where dripping water and ice can fall onto the unit.
Clear space for airflow on all sides per the manual.
Defrost water drains away from walkways and driveways, where ice would be a slip hazard.
Not facing directly into prevailing winter wind if avoidable.
Accessible for clearing snow after storms.

The house matters as much as the heat pump

A leaky, poorly insulated house needs more heat on the coldest night, which means a bigger heat pump, more backup and higher running costs. Before or alongside a heat pump, consider:

Attic insulation up to R-50 to R-60; many older Ontario homes have only R-12 to R-20. See the attic insulation guide.
Air sealing. Older homes often test at 7–15 ACH50 on a blower door test. Bringing that down shrinks the design load. See the air sealing guide.
Ducts. Heat pumps deliver warm air at lower temperatures (often 30–40 °C) than a gas furnace. Leaky ducts in unheated spaces or undersized returns can make rooms feel drafty.

A pre-retrofit energy assessment through the Home Renovation Savings assessment stream can identify these issues and may unlock extra rebates. See our home energy assessment guide.

Comfort: what to expect

Heat pumps feel different from a furnace. Instead of short blasts of very hot air, a variable-speed heat pump runs for long periods at lower output. Many people find this more even and quieter. Others, used to hot air from a furnace register, find the cooler air feels less cosy at first. Air at 35 °C is still warmer than your skin, but on a cold night it can feel cool coming out of a register near a seating area.

Practical tips:

Keep the thermostat at a steady setting.
Make sure supply registers are not blowing directly at sitting areas.
Adjust fan settings with your installer so airflow is not excessive at low output.

Frequently asked questions

Will my heat pump stop working at −30 °C?

Many cold-climate models keep running near −30 °C at reduced output; some shut off at a set low temperature to protect the compressor. That is why a backup heat source is part of almost every Ontario design. Check the low-temperature cut-out in the product specifications.

Is a cold-climate heat pump worth it in Ottawa or Northern Ontario?

Often yes, especially if you heat with oil, propane or electric baseboards, but the design changes. In colder regions a hybrid system or a heat pump sized closer to the full design load makes sense, and running costs depend heavily on how many hours backup heat runs.

Why is steam coming out of my outdoor unit?

It is the defrost cycle melting frost off the coil. It normally lasts a few minutes. If the unit is covered in solid ice or defrosts constantly, call your installer.

Should I cover my outdoor unit in winter?

No. A heat pump runs all winter and needs open airflow. A small top shield to stop falling ice is fine if the manufacturer allows it, but never wrap the unit.