What COP should a heat pump have?

COP stands for coefficient of performance, and it is the standard measure of heat pump efficiency. There is no set limit for COP ratings: the higher the score, the greater the efficiency of the heat pump³. What counts as "good" depends on the type of heat pump, the test conditions, the state of the house and the season, which is why the seasonal figure, SCOP, matters more than any single COP reading.

COP explained: how much heat you get for each unit of electricity

The coefficient of performance is the amount of heat produced for every unit of electricity used⁶. It is calculated as heat output divided by power input, a formula set out in the official methodology behind heat pump assessments⁷. A heat pump with a COP of 3.0 delivers three units of heat for every unit of electricity it uses⁸.

Because a heat pump moves heat rather than burning fuel to create it, the ratio can exceed 1, which is what separates it from any resistive electric heater. The figure is always tied to specific test conditions: the outdoor temperature and the flow temperature at which the measurement was taken. A COP quoted without those conditions tells you little about how the system will behave in January.

The ideal COP for a heat pump

The official floor is low: for heat pumps providing space heating, the minimum COP is set at 1⁷. Building regulations go further for other types of heat pump, with a minimum COP of 3.0 for space heating and 2.0 for domestic hot water heating under the current Part L 2021 standard⁹.

Maker guidance sets higher reference points at specific test conditions: air-to-water heat pumps should have a COP of at least 4 at A2W35, brine-to-water heat pumps at least 4.5 at B0W35, and water-to-water heat pumps at least 5.5 at W10W35¹⁰. These are test-condition figures, not year-round averages, and they describe what a well-matched system can achieve at low flow temperature with a favourable heat source.

In practice, a household should treat COP 3 as the working benchmark and SCOP 2.8 as the regulatory minimum for grant eligibility. Anything below that in real operation points to a problem with the installation, the insulation or the flow temperature rather than the technology.

Comparing COP across air, ground and water source heat pumps

Air source heat pumps draw heat from the outside air, while ground source heat pumps extract it from the ground¹¹. That difference in heat source drives the difference in COP, because the ground stays at a more stable temperature than the air through a British winter.

A typical ground source heat pump can generate 3.5 to 4.5 units of heat for each unit of electricity it uses⁴. Ground-to-water systems are reported with a COP of up to 4.5¹². Against that, ground source heat pumps are a lot more expensive to install than air source systems¹³, and the heat they produce is at a lower temperature than other forms of heating, working best with underfloor heating, which requires lower flow temperatures than radiators⁴.

Water source systems sit at the top of the range because water carries a steady, relatively warm heat source, but they are only an option where a pond, lake, river or aquifer is accessible.

SCOP: why the seasonal measure counts more than one COP reading

The SCOP, or seasonal coefficient of performance, is the average COP across the whole year¹⁴. You will also see it called the Seasonal Performance Factor (SPF), which shows the heat pump's efficiency averaged across the whole year⁶. It is a way to rate a heat pump's performance in a given climate¹⁵, which makes it far more useful than a single COP reading taken on one day at one flow temperature.

SCOP is also the figure the rules use. Under the Boiler Upgrade Scheme, heat pumps must have a seasonal coefficient of performance (SCOP) of at least 2.8⁵, and the current installer guidance states that air-to-water and ground source systems must achieve an in situ SCOP of at least 2.8¹⁶. The scheme also requires that the heat pump meets the property's heating and hot-water demands and has a capacity of no more than 45 kWth¹⁷. The SCOP 2.8 requirement applies only to air-to-water systems, not to all heat pump types¹⁸.

When comparing quotes, ask for the SCOP rather than the headline COP, and check that the calculation reflects your home and climate rather than a generic assumption.

Factors that influence COP: outside temperature and flow temperature

Two variables dominate real-world COP: the temperature of the heat source and the flow temperature the system is asked to deliver. A warmer heat source, such as mild outdoor air or a stable ground loop, gives a higher COP, while a colder heat source combined with a higher required flow temperature gives a lower COP¹⁹.

The maker's own worked example shows the effect of flow temperature: a heat pump running at 45°C when the outside temperature is 2°C achieves a particular performance level³, and a heat pump running at a fixed 55°C flow temperature on a 10°C day achieves a lower COP than the same system would at a lower flow temperature²⁰. Running at 35°C instead of 55°C on a mild day can increase COP by 30 to 50%, depending on the system and heat pump type²⁰.

Winter pulls COP down from both directions. An air source heat pump is less efficient in winter when the air temperature is colder²¹, and overnight air temperature can drop by 5°C or more in winter, reducing efficiency further when the system is heating water to a high temperature²². A maximum flow temperature of 55°C is the typical recommendation for efficiency²³, and keeping flow temperatures as low as the emitters allow is the single biggest lever on COP a household controls after installation²⁴.

How a better COP cuts your running costs

COP feeds directly into running costs because it sets how much electricity each unit of heat consumes. The stakes are real: a heat pump operating at a low COP can end up costing more to run than a gas boiler, particularly in a poorly insulated home and without pricing reform¹.

At the other end, a household could save more than 50% on running costs with a heat pump compared with a gas boiler, but this requires high quality installation, high efficiency and a heat pump tariff²⁵. The same figure, of as much as 50% and more, is reported with the same conditions attached¹⁴. So a higher COP alone does not guarantee lower bills: the installation quality, the tariff and the fabric of the house all have to line up.

Insulation is the precondition. Topping up wall, floor and loft insulation before installing a heat pump helps reduce its running costs²⁶, and the COP figures above already assume it: 3 to 4 in a well-insulated home, around 2 or lower in a poorly insulated one¹. The government's Check if a heat pump could be suitable for you service compares the cost and carbon emission savings available and what is needed to install a heat pump²⁷, which is the natural next step for a household weighing the numbers.

For energy independence, COP is the measure of how far each unit of grid electricity is stretched into heat. A COP of 4 turns one imported unit into four units of warmth; a COP of 2 turns it into two. The dependence that remains is on electricity itself, its price relative to gas, and the tariff the household is on, which is why the largest reported savings pair high efficiency with a heat pump tariff rather than efficiency alone.