Do Heat Pumps Work in Cold Weather?

One of the most common concerns about heat pumps is whether they'll keep your home warm when temperatures drop. It's a fair question—after all, air source heat pumps extract heat from the outside air. But the reality is far more reassuring than many people expect.

How Heat Pumps Work in Cold Weather

Even cold air contains heat energy. At 0°C, air still contains about 80% of the heat energy it has at 20°C. Heat pumps use a refrigerant cycle (similar to a fridge in reverse) to extract this heat and concentrate it for your home.

Modern heat pumps use advanced technology to maintain performance in cold conditions:

• Enhanced vapour injection (EVI): Boosts efficiency at low temperatures
• Variable speed compressors: Adjust output to match demand
• Intelligent defrost cycles: Prevent ice buildup efficiently
• Low-temperature optimised refrigerants: R32 and R290 perform well in cold

Heat Pump Efficiency by Temperature

Outside Temp	Typical COP	Performance
10°C	4.0 - 4.5	Excellent
5°C	3.5 - 4.0	Very Good
0°C	3.0 - 3.5	Good
-5°C	2.5 - 3.0	Good
-10°C	2.0 - 2.5	Adequate
-15°C	1.8 - 2.2	Reduced

Key insight: Even at -10°C, a COP of 2.0-2.5 means you're getting 2-2.5 kWh of heat for every 1 kWh of electricity—still much better than direct electric heating (COP of 1.0).

UK Winter Temperatures

The UK has a mild maritime climate. Average winter temperatures across regions:

• Southern England: Average 4-7°C in winter
• Northern England: Average 3-5°C in winter
• Scotland: Average 1-4°C in winter
• Wales: Average 3-6°C in winter

Temperatures below -5°C are relatively rare in most of the UK, occurring just a few days per year in most areas. Below -10°C is exceptional.

Nordic Countries Prove Heat Pumps Work

If you're still sceptical, consider that countries with far harsher winters have embraced heat pumps:

• Norway: 60% of homes have heat pumps (average winter temps: -3°C to -7°C)
• Sweden: Over 1.5 million heat pumps installed (winters regularly below -10°C)
• Finland: Fastest-growing heat pump market (winters down to -20°C)

If heat pumps work in Scandinavia, they'll certainly work in Birmingham, Manchester, or Edinburgh.

What About Defrost Cycles?

When temperatures drop near freezing with high humidity, ice can form on the outdoor unit. Heat pumps handle this automatically:

• Built-in sensors detect ice formation
• The system briefly reverses to melt ice (typically 1-10 minutes)
• Modern systems minimise defrost frequency and duration
• You won't notice any comfort impact inside

Defrost cycles do use some energy, but this is already factored into seasonal efficiency ratings (SCOP).

Tips for Best Cold Weather Performance

1. Choose a quality brand: Mitsubishi, Daikin, Vaillant, and Samsung have excellent cold-weather performance
2. Ensure proper sizing: An undersized heat pump will struggle; proper sizing is crucial
3. Insulate your home: Better insulation means less heat demand in cold snaps
4. Use weather compensation: Smart controls adjust for outside temperature
5. Keep the outdoor unit clear: Ensure good airflow, remove snow/debris
6. Run continuously: Heat pumps work best maintaining steady temperatures rather than on/off operation

Frequently Asked Questions

Do heat pumps work when it's freezing outside?

Yes! Modern air source heat pumps work efficiently down to -15°C to -25°C. UK winters rarely drop below -5°C. Even at -10°C, a good heat pump achieves a COP of 2.0-2.5.

At what temperature does a heat pump stop working?

Modern heat pumps continue working down to -15°C to -25°C. They don't 'stop' but gradually become less efficient. UK installations rarely experience such extremes.

Are heat pumps suitable for the UK climate?

Absolutely. The UK's mild maritime climate (average winter 2-7°C) is ideal for heat pumps. Countries far colder have widespread adoption.