What SCOP can I expect from an air source heat pump?

SCOP stands for Seasonal Coefficient of Performance. It is the average COP across the whole year⁴, a way of rating a heat pump's performance in a given climate⁵. Because it averages performance across the seasons rather than measuring a single moment, it is the number that matters most for running costs, and it is the number grant schemes and building rules are written around.

The meaning of SCOP and the way it is calculated

SCOP is the average COP across the whole year⁴. Where COP (Coefficient of Performance) tells you how much heat a heat pump delivers for one unit of electricity at a given moment, SCOP takes in the whole heating season: cold days when the unit works hardest, mild days when it barely runs, and the standby electricity it draws in between. Air source heat pumps generally have a COP between 2.0 and 5.0⁹, but that single-point figure moves constantly with the weather, which is why the seasonal average is the more honest measure.

In Europe, SCOP is calculated according to EN 14825, which defines how seasonal efficiency must be determined under standardised conditions¹⁰. The British standard behind it, BS EN 14825:2013, covers "Air conditioners, liquid chilling packages and heat pumps with electrically driven compressors for space heating and cooling. Testing and rating at part load conditions and calculation of seasonal performance"¹¹. SCOP includes performance at multiple outdoor temperatures, part-load operation, standby and auxiliary electricity consumption, and, for air-source systems, defrost cycles¹⁰. In UK methodology, the EN 14825 test data is used in combination with calculations from BS EN 15316-4-2:2017 to calculate the performance of the installed system¹², so the figure reflects the set-up, not just the unit. More detail on the three efficiency measures is on our page on heat pump efficiency: COP, SCOP and SPF.

What SCOP to expect in a UK home: 3.0 to 4.0

The headline answer is around 3.0 in typical UK conditions¹, with 4.0 or more achievable where the installation suits it². The spread between those figures comes down to design. A household on standard electricity rates with typical medium usage, replacing a gas boiler, would need a heat pump with a SCOP of at least 2.9 before it started to make annual savings¹, so the typical figure sits just above the break-even point against gas on those assumptions.

Official consultations point the same way. Northern Ireland's building regulations discussion document proposes, for existing dwellings, a minimum SCOP of 3.0 for heating and 2.0 for domestic hot water for all systems other than direct expansion units¹³. A UK Government options assessment on raising minimum standards for heat pumps records that high-temperature air source heat pumps have SCOPs ranging from 2.55 to 3.25⁶, while low-temperature designs reach the higher end of the range. In practice, a household should treat 3.0 as the floor of expectation and 4.0 as a realistic target for a well-designed system, with anything above that dependent on emitters and insulation.

Flow temperature: the single biggest factor in your SCOP

Lower heating water temperatures improve efficiency significantly, and floor heating systems typically enable higher SCOP than high-temperature radiator systems¹⁰. This is why the same heat pump can return very different seasonal figures in different homes. Air source heat pumps usually run at lower flow temperatures of around 45 degrees centigrade⁸, and Edinburgh's local heat and energy efficiency strategy cites an optimal supply, or flow, temperature of 45°C with a return temperature of 40°C¹⁴. Ground source systems similarly benefit from operating at flow temperatures below 55°C¹⁵.

The trade-off is speed. Lowering the heat pump's flow temperature reduces the reaction time of the heating system, meaning it takes longer to warm the home¹⁶. High-temperature units, which exist to work with existing radiators, pay for that convenience in efficiency: their SCOPs range from 2.55 to 3.25⁶. Our page on what flow temperature heat pumps use for space heating covers the practical side, and radiators, underfloor heating and emitters explains how emitter choice sets the temperature the system can run at.

Boiler Upgrade Scheme eligibility and the 2.8 minimum SCOP requirement

The Boiler Upgrade Scheme requires that an air-to-water heat pump must achieve an in-situ seasonal coefficient of performance (SCOP) of at least 2.8⁷. Ofgem's scheme rules state the same minimum SCOP rating of 2.8 for eligible air-to-water and ground source heat pumps¹⁷, and the heat pump must meet the property's heating and hot-water demands with a capacity of no more than 45 kWth¹⁸. The scheme provides £7,500 towards the cost of an air source or ground source installation¹¹; earlier guidance recorded grants of £5,000 for air source heat pumps and £6,000 for ground source, before the increase¹⁹.

Two points of scope matter. The 2.8 requirement applies only to air-to-water systems, not to all heat pumps²⁰, which is why air-to-air heat pumps do not qualify for the grant. And 2.8 is a floor for funding, not a target for a good installation: the Heat Pump Association's statistics use a SCOP of 2.8 for hydronic heat as a conservative planning assumption²¹, well below what a low-temperature system should deliver. Older scheme rules elsewhere set a minimum Seasonal Performance Factor of 2.5²², showing how the official floor has tightened over time. The full funding picture is on our page on heat pump grants and funding across the UK.

How weather compensation affects seasonal efficiency across the year

Most modern heat pumps feature a weather compensation function that automatically adjusts indoor temperature based on outdoor conditions²³. Weather compensation is the control method where the system varies the flow temperature according to the season²⁴, and it is the main reason a heat pump's efficiency is not one number but a curve through the year. On a mild autumn day the unit runs at a low flow temperature and high efficiency; in a cold snap it raises the flow temperature and works harder for each unit of heat.

This is also why the SCOP quoted before installation is an estimate rather than a promise. Until recently, the MCS 031 performance estimation method used the Seasonal Coefficient of Performance, based on a presumed flow temperature, to estimate the Seasonal Performance Factor and calculate the electricity required to deliver the annual heat demand²⁵. The seasonal measures you may see quoted, SCOP or Seasonal Performance Factor (SPF), show efficiency averaged across the whole year²⁴, and the two are not always used interchangeably by installers and manufacturers. Air source heat pumps can extract heat from the air even at temperatures as low as -15°C²⁶, but efficiency at that point is far below the seasonal average. How the controls are set up is covered in more depth on our page on heat pump controls, weather compensation and smart operation.

Heat pumps with the best SCOP ratings

The highest figures belong to units designed for low flow temperatures. One UK-listed model, the Vaillant aroTHERM split air source heat pump, is quoted with a SCOP of up to 4.88¹², and air source heat pumps are described as up to 400% efficient in independent consumer guidance¹⁶, consistent with a SCOP of 4.0. A maker's guidance states that an average air-to-water heat pump reaches a SCOP between 3.5 and 4.5, while top models go above 6³, though the top-end figures assume conditions such as underfloor heating and a well-insulated building that many homes cannot match.

At the other end, high-temperature air source heat pumps range from 2.55 to 3.25⁶. The pattern across the market is consistent: the model matters less than the temperature it is asked to run at. A mid-range unit on underfloor heating will usually out-perform a premium unit on old radiators. Comparisons of specific ranges, including high-temperature heat pumps, are covered elsewhere on the site.

What SCOP means for a household's energy independence

A SCOP of 3.0 to 4.0 means that for every unit of electricity a household buys, three to four units of heat arrive in the home, with the balance drawn from the outside air. That is the core of the independence case for a heat pump: the fuel is partly ambient and free, and the bought portion can come from any electricity source, including a rooftop and a battery, which is the direction of travel described in our guide to heat pumps and household energy independence.

The dependence that remains is real. The household still needs electricity from the grid or a supplier on the coldest days, when SCOP is at its weakest and demand is at its highest, and the quoted figure depends on the manufacturer's test data and the installer's design assumptions. A higher SCOP narrows that dependence: less electricity bought per unit of heat means lower bills and less exposure to price rises. That is why the flow temperature, the emitters and the controls, which together set the SCOP a home actually achieves, matter more to long-run independence than the badge on the outdoor unit. The starting point for the whole subject is our full guide to heat pumps.