Do heat pumps work in cold weather?
Short answer
Yes. Air-source heat pumps are designed to keep operating below freezing, and many models are rated for outdoor temperatures around -15°C to -20°C. Their efficiency falls as the temperature drops, so correct sizing matters. A system that struggles in ordinary UK winter weather is more likely to have a design, installation or control problem.
Last checked 24 September 2026 · 2 sources
How can a heat pump work when the air is freezing?
Freezing air still contains heat energy.
The refrigerant in the outdoor unit is colder than the outside air, so it can still absorb heat. The compressor then raises the refrigerant’s pressure and temperature so that heat can be transferred into the home.
The colder it gets outside, the harder the heat pump has to work. That is why performance at low temperatures is part of the design process.
What happens to efficiency in very cold weather?
Efficiency normally drops as outdoor temperature falls and the required heating-water temperature rises.
That does not mean the unit stops working. It means the coefficient of performance can be lower on the coldest days than in mild weather.
A good design accounts for this when sizing the heat pump and radiators.
What about frost on the outdoor unit?
Frost is normal in cold, damp conditions.
The heat pump periodically runs a defrost cycle to warm the outdoor coil and melt the ice. You may see steam or a sudden flow of water beneath the unit during this process.
Persistent heavy ice, repeated faults or a unit buried in ice should be checked.
Are heat pumps used in colder countries?
Yes. The source interview points to widespread use in Scandinavia as practical evidence that the technology itself is not limited to mild climates.
The exact performance still depends on the model and system design, so check the manufacturer’s operating range rather than relying on a general claim.
What should I do next?
Ask your installer what outdoor design temperature they have used, what heat output the chosen model provides at that temperature, and whether backup heating is expected to operate.
Sources
- Source interview with Heat Geek installer, cold-weather discussion.
- Manufacturer operating ranges should be checked for the specific model before publication or quotation.
Last checked: 24 September 2026