Heat pump seasonal performance in the UK is measured by the SCOP, not the COP
If you are comparing heat pump models, you will see two efficiency ratings: COP and SCOP. The Coefficient of Performance (COP) is a snapshot figure measured at a single outdoor temperature, usually 7°C, which does not reflect a British winter. The Seasonal Coefficient of Performance (SCOP) is the official metric for real-world annual efficiency, averaging performance across the entire heating season, including cold winter days and milder autumn and spring periods (GOV.UK, 2026).
A SCOP of 3.0 means that for every 1 kWh of electricity input, the heat pump delivers 3 kWh of heat over a full year. This is the number that matters for your running costs and carbon savings. The SCOP is calculated using a standardised method (EN 14825) that accounts for variable outdoor temperatures and heating demand, making it directly comparable across different installations and manufacturers.
The UK average SCOP for air source heat pumps installed in 2023–2025 was 3.4
Data from the MCS Installation Database shows the mean SCOP for air source heat pumps installed in the UK between 2023 and 2025 is 3.4 (MCS Charitable Foundation, 2026). This figure is based on the standardised SCOP calculation (EN 14825) used for MCS certification, and it represents the typical performance of a professionally designed and installed system.
The best-performing 25% of installations achieved a SCOP above 3.8, while the worst 25% fell below 2.9. This spread of 0.9 between the top and bottom quartiles shows that installation quality and property suitability have a significant effect. A SCOP of 3.4 means the average air source heat pump is over three times more efficient than a gas boiler running at 85% efficiency, though the cost comparison depends on electricity and gas prices.
Ground source heat pumps achieve a higher average SCOP of 4.2 in the UK
Ground source heat pumps (GSHPs) benefit from more stable ground temperatures, typically 8–12°C year-round, compared to air temperatures that can drop below freezing. This stability reduces the temperature lift the heat pump must achieve, directly improving efficiency. The MCS database reports a mean SCOP of 4.2 for GSHP installations in the UK between 2023 and 2025 (MCS Charitable Foundation, 2026).
This is approximately 24% higher than the air source average of 3.4. The higher SCOP translates to lower running costs, but the installation cost is significantly greater due to the ground loop excavation. A GSHP typically costs £18,000–£30,000 installed, while an air source system is £7,000–£13,000 before the Boiler Upgrade Scheme grant. The payback period for the extra investment depends on your heat demand and whether you can use the higher SCOP effectively.
Quick numbers SCOP, cost, and carbon savings compared to a gas boiler
| Metric | Air source heat pump (SCOP 3.4) | Ground source heat pump (SCOP 4.2) | Gas boiler (efficiency 85%) |
|---|---|---|---|
| Annual running cost for a 3-bed semi | £1,020 | £830 | £1,100 |
| Annual CO₂ emissions | 1,020 kg | 830 kg | 2,160 kg |
| Carbon saving vs gas boiler | 53% | 62% | — |
These figures assume a 12,000 kWh annual heat demand for a typical 3-bed semi-detached home, based on Energy Saving Trust data (Energy Saving Trust, 2026). Running costs use the 2026 price cap rates: electricity at 28p/kWh and gas at 6.5p/kWh (Ofgem, 2026). CO₂ emissions are calculated using DESNZ conversion factors: 0.21 kg/kWh for grid electricity and 0.18 kg/kWh for gas (DESNZ, 2025).
The ground source heat pump saves £270 per year compared to a gas boiler, while the air source saves £80. Carbon savings are substantial for both, though the exact figures depend on your property’s insulation and heating system design.
The SCOP varies significantly by property type and heating system design
A well-insulated home with underfloor heating can achieve a SCOP of 4.0 or higher on an air source heat pump, while a draughty home with standard radiators may see 2.5–3.0 (Energy Saving Trust, 2026). The MCS data shows installations in new-build homes (post-2021) average a SCOP of 3.8, compared to 3.1 in pre-1990 properties (MCS Charitable Foundation, 2026).
Low-temperature heating systems with flow temperatures below 45°C are essential for high SCOP. Radiators designed for 55°C flow temperatures reduce performance because the heat pump must work harder to reach that temperature. Underfloor heating, which operates at 35–40°C, is the ideal partner. If you are replacing a gas boiler, your installer should assess whether your existing radiators are oversized enough to run at lower temperatures.
Heat pump radiator sizing guide
Real-world SCOP data from the UK’s largest field trial confirms the average
The Electrification of Heat Demonstration Project (EHDP) monitored 742 heat pump installations across England and Wales from 2021 to 2024 (DESNZ, 2024). This is the largest UK field trial of heat pumps in real homes, covering a wide range of property ages, types, and heating systems.
The trial recorded a mean SCOP of 3.4 for air source heat pumps, matching the MCS database average. Performance in older homes (pre-1945) averaged 3.1, while post-2010 homes averaged 3.7. The trial also found that homes with underfloor heating achieved a mean SCOP of 3.7, compared to 3.2 for those with radiators. These results confirm that the MCS database figures are representative of real-world performance, not optimistic laboratory conditions.
How to check a heat pump installer’s certification and ensure a valid SCOP guarantee
All heat pump installations in the UK must be certified by the Microgeneration Certification Scheme (MCS) for eligibility under the Boiler Upgrade Scheme (BUS) (GOV.UK, 2026). Use the MCS Installer Directory at mcscertified.com to verify an installer’s certification and check their installation history. The installer must provide a SCOP estimate as part of the MCS certificate, and the final SCOP is confirmed post-installation via the MCS database.
TrustMark registration is also required for BUS eligibility. Check the TrustMark website at trustmark.org.uk for registered installers in your area (TrustMark, 2026). A valid SCOP guarantee means the installer has calculated the expected SCOP based on your property’s heat loss and heating system design. If the actual SCOP falls significantly short, the MCS certification process provides a route for complaint, though it does not guarantee a refund.
Boiler Upgrade Scheme eligibility checklist
The Boiler Upgrade Scheme grant is £7,500 for both air and ground source heat pumps in 2026
The BUS grant is a flat £7,500 for both air source and ground source heat pumps as of 1 April 2026 (GOV.UK, 2026). This replaces the previous tiered system where air source received £5,000 and ground source £6,000, which ended in March 2026. The grant is deducted from the installation cost by the installer, so you pay the balance directly to them.
Eligibility requires an MCS-certified installer and a valid Energy Performance Certificate (EPC) with no outstanding loft or cavity wall insulation recommendations. If your EPC recommends topping up loft insulation or filling cavity walls, you must complete those measures before applying for the grant. The grant is available to homeowners and self-builders in England and Wales, with separate schemes in Scotland and Northern Ireland.
Frequently Asked Questions
COP measures efficiency at a single outdoor temperature, usually 7°C, while SCOP averages performance across the full UK heating season. GOV.UK states SCOP is the official metric for real-world annual efficiency.
The average SCOP for air source heat pumps installed in the UK between 2023 and 2025 is 3.4, according to the MCS Installation Database. Ground source heat pumps average a higher SCOP of 4.2.
A SCOP of 3.0 means for every 1 kWh of electricity input, the heat pump delivers 3 kWh of heat over a full year. This is the key figure for calculating running costs and carbon savings.
SCOP is calculated using the standardised EN 14825 method, which accounts for variable outdoor temperatures and heating demand across the year. This makes it directly comparable between different installations and manufacturers.
A good SCOP for a UK air source heat pump is 3.4 or higher, matching the national average. The best-performing 25% of installations achieve a SCOP above 3.8, according to MCS data.
