Do Heat Pumps Work in Winter? UK Performance Data

The Big Question: Can a Heat Pump Really Heat Your Home in a British Winter?

Yes — emphatically. Modern air source heat pumps are rated to operate down to at least -20C, and the UK Electrification of Heat Demonstration Project (monitoring over 700 real installations) found that no monitored installation dropped below a COP of 2.0 even during the coldest conditions. At the average UK winter temperature of approximately 7C, a well-installed heat pump achieves a COP of 3.5–4.0. For a three-bedroom semi-detached home, that means winter running costs are broadly similar to gas — and significantly lower on a smart electricity tariff (Energy Saving Trust).

Related reading: Heat pump running costs: what do you actually pay? | Is your home suitable for a heat pump?

How Heat Pumps Extract Heat in Cold Weather

An air source heat pump does not generate heat the way a gas boiler does. Instead, it uses a refrigerant cycle to absorb heat energy from outdoor air and concentrate it to a useful temperature inside your home. Even at -15C, the outdoor air contains significant thermal energy — the only temperature at which air has no extractable heat is absolute zero (-273C).

The refrigerant inside the heat pump has an extremely low boiling point (around -25C to -40C depending on the system). When outdoor air passes over the evaporator coil, the refrigerant absorbs heat from the air, evaporates into a gas, and is then compressed to raise its temperature to 45–55C — more than enough to heat your radiators and hot water.

Temperature vs COP: Real UK Performance Data

The Coefficient of Performance (COP) measures how efficiently a heat pump converts electricity into heat. A COP of 3.0 means you get 3 kWh of heat for every 1 kWh of electricity consumed.

COP varies with outdoor temperature. Here is real-world performance data from UK installations:

Key point: Even at -10C — which is exceptionally rare in London, Surrey, and the South East — a heat pump still produces roughly twice as much heat energy as the electricity it consumes. Compare that to a gas boiler, which can never exceed 100% efficiency (a modern condensing boiler achieves around 92%).

What the Electrification of Heat data tells us

The UK government’s Electrification of Heat Demonstration Project, which monitored over 700 real-world heat pump installations across the country between 2020 and 2024, found that:

• The average seasonal COP (SCOP) across all installations was 2.8, with well-installed systems regularly achieving 3.0–3.5
• Performance dropped in winter months but never fell below a COP of 2.0 in any monitored installation
• Properties with proper system design and good insulation consistently achieved SCOPs above 3.2 year-round
• The single biggest factor affecting performance was installation quality, not outdoor temperature

This data demonstrates that heat pumps work reliably in UK winters — and that choosing an experienced installer working under MCS certification is more important than worrying about the weather.

Defrost Cycles: What They Are and Why They Are Normal

When outdoor temperatures drop close to or below freezing, frost can form on the outdoor unit’s evaporator coil. This is perfectly normal and expected.

How defrost works

When the heat pump detects frost building up (typically through sensors measuring coil temperature and airflow), it temporarily reverses the refrigerant cycle to send warm refrigerant through the outdoor coil, melting the frost. This takes approximately 2 to 5 minutes and happens periodically — perhaps every 30 to 90 minutes in sustained freezing conditions.

Does defrost reduce efficiency?

Yes, slightly. During a defrost cycle, the heat pump uses energy to melt frost rather than heat your home. This is already factored into the seasonal COP figures in the table above. In practice, defrost cycles reduce overall winter efficiency by roughly 5–10%.

What you might notice

During a defrost cycle, you may see steam rising from the outdoor unit and hear the fan stop briefly. The indoor heating continues from the buffer in the system, so you will not feel any drop in room temperature. This is completely normal — it is not a fault.

Myths vs Reality

Myth 1: “Heat pumps stop working below 0C”

Reality: Modern air source heat pumps are rated to operate down to at least -20C. Leading brands like Mitsubishi Ecodan, Vaillant Arotherm Plus, and Samsung Gen7 are all tested and guaranteed to operate at -20C. The coldest temperature recorded in London in the past decade was approximately -7C.

Related reading: Best heat pump brands UK 2026

Myth 2: “You need a backup gas boiler for cold snaps”

Reality: A correctly sized heat pump does not need any backup heating system. During the design stage, your installer calculates the heat loss of your property at the coldest design temperature for your area (typically -3C to -5C for southern England) and sizes the heat pump to meet 100% of that demand.

Myth 3: “Heat pumps only work in well-insulated new-build homes”

Reality: Heat pumps work in all types of property, including Victorian terraces, 1930s semis, and older detached houses. Better insulation means the heat pump can be smaller and run more efficiently, but it is not a prerequisite.

Myth 4: “Electricity is so expensive that running a heat pump in winter costs more than gas”

Reality: At winter COP levels of 2.5–3.0, a heat pump is broadly cost-neutral with gas at 2026 prices. At a COP of 3.0 with electricity at 24.5p/kWh (Ofgem), your cost per kWh of heat is approximately 8.2p. Gas at 7.4p/kWh with a 92% efficient boiler gives approximately 8.0p per kWh of heat (Ofgem). They are essentially level on a standard tariff — but the heat pump gets cheaper as COP rises, while the gas boiler cannot improve. On a smart tariff, the heat pump is considerably cheaper.

Related reading: Air source heat pump vs gas boiler: running costs compared

Tips for Maximising Winter Efficiency

1. Let it run low and slow

Heat pumps are most efficient when running continuously at a low flow temperature (35–45C) rather than cycling on and off. Set your thermostat to a steady temperature and let the heat pump maintain it gently.

2. Use weather compensation

Most modern heat pumps have a weather compensation feature that automatically adjusts the flow temperature based on outdoor conditions. When it is mild, the system runs at a lower temperature. When it is cold, it increases the flow temperature. This is far more efficient than a fixed flow temperature.

3. Keep the outdoor unit clear

Ensure the outdoor unit has at least 300mm of clear space on all sides for airflow. Do not box it in, cover it, or allow leaves, snow, or debris to accumulate around it.

4. Optimise your heating schedule

Rather than heating the house from cold each morning, use a setback approach: let the temperature drop by 2–3C overnight rather than switching off completely. The heat pump can then gently raise the temperature in the morning without needing a burst of high-temperature output.

5. Consider a smart electricity tariff

Time-of-use tariffs like Octopus Agile or Intelligent Octopus Go offer electricity at 7–10p/kWh during off-peak hours (typically overnight). Running your heat pump to pre-heat your home and hot water cylinder during these periods can dramatically reduce your winter bills.

6. Combine with solar panels

Even in winter, solar panels generate electricity on bright days. A 4 kWp system in southern England will produce 100–200 kWh in December and January — not as much as summer, but still enough to offset a meaningful portion of your heat pump’s electricity consumption.

Related reading: Solar panels and heat pumps: the perfect combination

What About the Coldest Week of the Year?

During the coldest week of a typical UK winter (sustained temperatures around -2C to -5C for a week in January), here is what you can expect for an average three-bedroom semi-detached home with a properly sized 8 kW heat pump:

• Average COP during that week: 2.5–3.0
• Heat demand: approximately 60–80 kWh per day
• Electricity consumption: approximately 20–30 kWh per day
• Daily cost at standard rate (24.5p, Ofgem): £4.90–£7.35
• Daily cost on smart tariff (~10p off-peak): £2.00–£3.00

For comparison, a gas boiler heating the same property in the same conditions would use approximately 65–85 kWh of gas per day at 7.4p/kWh (Ofgem), costing £4.81–£6.29 per day.

The costs are remarkably similar — and the heat pump owner simultaneously reduces carbon emissions by over 60% and operates a system designed to last 20–25 years rather than 12–15.

How Electromatic Can Help

Electromatic M&E Ltd offers free home surveys across London and Surrey (TW, KT, SW postcodes). We handle BUS Grant applications (subject to eligibility), install ASHP and solar PV from a single contractor, and deliver within 2–4 weeks of survey confirmation. All work is carried out under MCS certification via our accredited umbrella partner. We carry out a detailed heat loss assessment of your property and design a system that keeps you comfortable throughout the coldest UK winters.

Book your free home survey →

Call us: 07718 059 284 | Email: admin@electromatic.uk

Frequently Asked Questions

Do heat pumps work when it snows?

Yes. Snow does not affect the heat pump’s ability to extract heat from the air. The only concern is ensuring the outdoor unit is not buried in drifted snow, which could restrict airflow. The unit is typically mounted on a stand 200–300mm off the ground, and the fan naturally disperses snow. In heavy snowfall, a quick brush-off is all that is needed.

What is the lowest temperature a heat pump can work at?

Most modern air source heat pumps are rated to operate down to -20C or -25C. In London and the South East, temperatures below -10C are virtually unheard of. Your heat pump will comfortably handle any conditions the British climate is likely to produce.

Do I need to change my radiators for a heat pump to work in winter?

Not necessarily. Many existing radiators are oversized for the rooms they serve (a legacy of poor insulation when the house was built). A heat loss calculation during your survey will identify whether any radiators need upgrading. Typically, only a few radiators need to be swapped for larger models — usually at a cost of £200–£500 each.

Will my heat pump cope during a Beast from the East-style cold snap?

Yes. The Beast from the East in 2018 saw temperatures drop to -5C to -10C across southern England for several days. Heat pumps that were installed at the time continued operating without issue. Modern units are even more capable. Your system is designed for a design temperature of -3C to -5C, meaning it can meet full heat demand at those temperatures.

Is underfloor heating essential for a heat pump to work in winter?

No. Underfloor heating is the ideal partner for a heat pump because it operates at low flow temperatures (30–35C), which maximises COP. But standard radiators work perfectly well with heat pumps — they run at slightly higher flow temperatures (40–50C), which reduces COP marginally. Most UK heat pump installations use existing radiators successfully throughout winter.

The information in this article is for general guidance only and does not constitute financial, legal, or technical advice. Performance data is based on the UK government’s Electrification of Heat Demonstration Project and Energy Saving Trust data. Actual performance depends on your property type, insulation levels, system design, and electricity tariff. Energy price figures use Ofgem’s April 2026 price cap (electricity 24.5p/kWh, gas 7.4p/kWh). The Boiler Upgrade Scheme (BUS) grant of £7,500 is subject to eligibility criteria set by Ofgem — not all properties qualify. Electromatic M&E Ltd operates under MCS certification via our accredited umbrella partner. All installations comply with Building Regulations Part L and MCS standards. E&OE.

Written by Electromatic M&E Ltd — ASHP & Solar installer, London & Surrey (electromatic.uk)

Last updated: April 2026 | Electromatic M&E Ltd, Company No. 13837345