The short answer
COP (Coefficient of Performance) and SCOP (Seasonal Coefficient of Performance) both measure how efficient a heat pump is — how many units of heat output it delivers per unit of electricity input. A COP of 4 means the pump produces 4 kWh of heat for every 1 kWh of electricity. COP is a single snapshot measured at fixed test conditions, so it changes with outside temperature and flow temperature. SCOP is the more useful real-world figure: it is the average efficiency across a whole heating season, accounting for the range of weather a UK winter brings. A typical well-designed UK heat pump achieves a SCOP of around 3.0 to 4.0. The lower the flow temperature you run your system at, the higher both figures climb — which is why radiator sizing and insulation matter so much to running costs.
When comparing heat pumps or judging a quote, SCOP is the number to focus on. Knowing what it means — and how a single COP figure can be quoted at a flattering condition — helps you read the specifications honestly.
SCOP and COP at a glance
- COPEfficiency at one fixed test condition
- SCOPAverage efficiency across a heating season
- COP / SCOP of 4 means4 kWh heat per 1 kWh electricity
- Typical UK SCOPAround 3.0 to 4.0
- Biggest factorFlow temperature (lower = higher SCOP)
Why these numbers matter to your bills
Efficiency figures are not an abstract specification — they translate almost directly into running cost. A heat pump runs on electricity, which in the UK costs more per kWh than gas. The efficiency multiplier is what closes that gap: if a pump delivers 3.5 units of heat per unit of electricity, you are effectively buying heat at a fraction of the raw electricity price.
Put simply, the heat your home actually needs across a year is roughly fixed by its insulation and the weather. The SCOP decides how much electricity you have to buy to supply that heat. A system running at a SCOP of 4.0 uses noticeably less electricity than the same home on a SCOP of 2.8 — and that difference shows up on every bill, every month, for the life of the system. This is why it is worth understanding the figures before you sign off a design, rather than treating them as installer jargon.
COP: a single-condition snapshot
COP is the ratio of heat produced to electricity consumed at a specific set of conditions — for example, a stated outside air temperature and a stated flow temperature. A pump quoted as "COP 4.5" might achieve that only when it is mild outside and the flow temperature is low.
Because conditions in the real world vary constantly, a single COP figure can be misleading if quoted at flattering test points. It is genuinely useful for comparing two pumps at the same stated conditions, but on its own it does not tell you how the pump will perform across a whole British winter.
An analogy helps. COP is like a car's fuel economy measured at a steady 50 mph on a flat road — a real number, useful for comparison, but not what you will see in mixed driving. A pump's COP is highest on a mild day with a low flow temperature, and falls as the outside air gets colder or the flow temperature is pushed up to satisfy small radiators. Two pumps can share the same headline COP yet behave quite differently once the weather turns, because the test point chosen for the quote was kind to one and not the other. That is exactly why a seasonal figure is needed to judge real-world cost.
SCOP: the seasonal average that actually matters
SCOP solves the snapshot problem by averaging efficiency across the range of temperatures a heating season throws at the pump. It is calculated to a European standard using a defined climate profile, so it reflects performance across mild and cold days combined.
This makes SCOP the figure to compare when choosing a heat pump and the one used to estimate running costs. A SCOP of 3.5, for example, means that over a typical year the pump delivers 3.5 units of heat per unit of electricity. The higher the SCOP, the less electricity the pump uses to keep the home warm.
One important caveat is that the SCOP printed on a manufacturer's data sheet is tied to a particular flow temperature — often a low one that produces an impressive headline figure. The SCOP your installation actually achieves depends on the flow temperature your home needs, which is set by your radiators and insulation. A pump rated at SCOP 4.5 at a 35 °C flow may deliver closer to 3.0 if your emitters force it to run at 55 °C. This is why the design SCOP, calculated for your specific system, is far more meaningful than the best-case laboratory number, and why a good installer will quote the figure expected for your home rather than the brochure maximum.
| Term | What it measures | Best used for |
|---|---|---|
| COP | Efficiency at one fixed condition | Comparing pumps at identical test points |
| SCOP | Average efficiency over a heating season | Estimating real running costs |
How COP and SCOP differ. Sources: Energy Saving Trust; MCS.
Why flow temperature drives the numbers
The single biggest lever on heat pump efficiency is the flow temperature — the temperature of the water the pump sends to your radiators or underfloor heating. The smaller the gap the pump has to bridge between the heat source and the flow temperature, the less work the compressor does, and the higher the COP and SCOP.
Running a system at 35 °C flow (typical of underfloor heating) yields a much higher SCOP than running it at 55 °C. That is why heat pump installations focus on larger radiators or underfloor heating and good insulation: they allow a comfortable home at a low flow temperature, which keeps the SCOP — and therefore running costs — favourable. A well-designed low-temperature system is the difference between a heat pump that is cheap to run and one that disappoints.
As a rough rule of thumb, every few degrees you can shave off the flow temperature lifts the SCOP by a meaningful margin, so the radiator and insulation work that lets a home run cooler pays back through lower bills for as long as the system lasts. This is why two identical pumps in two similar houses can post very different seasonal efficiencies: the one feeding generous radiators in a well-insulated home runs cool and efficient, while the one forced to push hot water through small radiators in a draughty home never reaches its potential. The number on the data sheet is only ever realised by the system design around it.
Frequently asked questions
Is a higher SCOP always better?
For running costs, yes — a higher SCOP means more heat per unit of electricity and lower bills. But SCOP depends heavily on the design flow temperature, so a high quoted figure only helps if your system is actually designed to run at that low temperature. The real-world SCOP your installation achieves matters more than a headline manufacturer number.
What's a good SCOP for a UK heat pump?
A well-designed UK air source installation commonly achieves a SCOP of around 3.0 to 4.0, and ground source can be a little higher. Figures around 3.5 and above generally indicate a system designed to run at a sensibly low flow temperature with correctly sized emitters. Much lower figures often point to undersized radiators forcing a high flow temperature.
Does COP change with the weather?
Yes. COP falls as the outside temperature drops, because the pump has to work harder to extract and upgrade heat from colder air. That is exactly why SCOP exists — it averages performance across the whole range of seasonal conditions rather than reporting a single favourable moment.
Sources & further reading
Figures on this page are typical UK ranges drawn from published sources and depend on your specific home. They are guidance, not a quotation or guaranteed saving.