Heat Pumps
Do Heat Pumps Work in BC Cold Snaps? Cold-Climate Performance Explained
Yes — with the right equipment and design. What actually happens inside a heat pump at -20°C, and the questions that separate a cold-ready install from a cold-weather complaint.
Published 2026-07-15 · Updated 2026-07-15 · Retrofit Network
What happens inside a heat pump when it gets cold
A heat pump moves heat from outdoor air into your home. There is still plenty of heat energy in air at -20°C, but extracting it takes more compressor work, so two things happen as temperature falls: efficiency (COP) drops, and maximum heating output (capacity) drops. Older single-speed units lost capacity quickly below freezing; modern cold-climate inverter units use variable-speed compressors, enhanced vapour injection, and better refrigerant management to hold far more of their capacity at low temperatures.
Manufacturers publish this as a capacity table: for example, a unit might deliver 100% of rated capacity at 8°C, around 70–80% at -15°C, and 50–60% at -25°C. Those numbers vary by model — asking for the table is one of the fastest ways to tell serious equipment from marketing.
BC's actual cold: coast vs Interior vs North
Coastal BC (Metro Vancouver, Victoria, the Sunshine Coast) has design temperatures around -5°C to -9°C — mild by Canadian standards. Even the coast's occasional Arctic outflow events, which can drive temperatures to -10°C to -15°C with wind, sit comfortably inside modern cold-climate ratings. The Southern Interior (Kelowna, Kamloops) designs around -15°C to -20°C, and Prince George and the North around -30°C or below.
The design implication: on the coast, most quality inverter heat pumps handle winter without drama. In the Interior, cold-climate-rated equipment should be considered the default. In the North, cold-climate equipment plus a robust backup source is standard practice.
Sizing and the 'design temperature' conversation
A proper install starts with a heat-loss calculation for your home and your region's outdoor design temperature — the temperature your location stays above roughly 99% of heating hours. The installer then checks the equipment's published capacity at that temperature, not its nameplate rating at 8°C. A system sized only by square footage or by nameplate tonnage is the root cause of most 'my heat pump can't keep up' stories.
Slight oversizing for cold snaps is a design choice with trade-offs (cost, cycling, summer comfort), which is why the standard answer is right-sizing plus backup rather than a huge unit.
Backup heat: what it is and when it runs
Most BC systems include one of three backup strategies. Electric resistance strips inside the air handler: simple and cheap to install, expensive per hour to run, and only active during the coldest hours. Dual-fuel: keeping a gas furnace as the below-threshold heat source — common in Interior retrofits. Existing baseboards: in homes converting from electric baseboard, the baseboards simply stay as zone backup.
A well-designed system might run backup heat a few dozen hours a year in the Interior and almost never on the coast. If backup is running weekly in mild weather, something is wrong with sizing, refrigerant charge, or controls — that's a service call, not a technology failure.
Defrost cycles and other cold-weather behaviours to expect
In cold, humid weather the outdoor coil frosts up, and the unit periodically runs a defrost cycle — you may see steam rising from the outdoor unit and hear a whooshing sound as the system briefly reverses. This is normal. Also normal in deep cold: longer continuous run times (inverter systems are designed to run steadily rather than cycle) and slightly cooler supply air than a gas furnace blast — the house stays at temperature, the air from the vents just feels less hot.
What's not normal: ice completely encasing the outdoor unit, backup heat running constantly, or indoor temperatures sagging for hours. Those warrant a call to your installer.
FAQ
Do heat pumps stop working below freezing?
No. Modern cold-climate units produce useful heat down to roughly -25°C to -30°C. Output and efficiency decline as temperature drops, which is why sizing against your region's design temperature matters.
What happened to heat pumps in BC's January 2024 cold snap?
Properly sized cold-climate systems kept homes warm through the -15°C to -30°C Arctic outflow, often with some backup-heat hours. Underperforming cases traced overwhelmingly to undersized or non-cold-climate equipment — a design issue, not a technology limit.
Do I need backup heat on the BC coast?
Many coastal installs run without meaningful backup, but most designers still include a modest backup source (electric strips or retained baseboards) for resilience during rare extreme events. It's cheap insurance that runs a handful of hours a year.
Is steam coming off my outdoor unit a problem?
No — that's a normal defrost cycle melting frost off the outdoor coil in cold, humid weather. It typically lasts a few minutes and the system returns to heating automatically.
What should I ask an installer about cold-weather performance?
Ask for the equipment's published capacity at your region's design temperature, the heat-loss number they calculated for your home, and what the backup heat strategy is. Confident, specific answers to those three questions are the mark of a cold-ready design.
Are cold-climate models worth the extra cost in Metro Vancouver?
They're not strictly necessary on the coast, but the premium buys better cold-snap output and often better part-load efficiency. In the Interior and North, cold-climate rating should be treated as a requirement, not an upgrade.
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