Heat Pump COP Explained: What UK Homeowners Need to Know

When you start researching heat pumps, one number comes up more than any other: COP. It stands for Coefficient of Performance, and it is the single most important figure for understanding how much a heat pump will cost you to run. Yet it is also one of the most misunderstood.

This guide explains what COP actually means, how to interpret the numbers you see in manufacturer brochures, and why the real-world performance of your heat pump might differ from those headline figures.

What Is COP?

COP stands for Coefficient of Performance. It measures how much heat energy a heat pump produces for each unit of electrical energy it consumes.

A COP of 3.0 means the heat pump generates 3 kWh of heat for every 1 kWh of electricity it uses. A COP of 4.0 means 4 kWh of heat per 1 kWh of electricity.

To put that in context, a conventional electric heater has a COP of exactly 1.0. It converts 1 kWh of electricity into 1 kWh of heat. A gas boiler converts around 0.9 kWh of gas into 0.9 kWh of useful heat (roughly 90% efficiency). A heat pump with a COP of 3.0 is effectively 300% efficient, producing three times more heat energy than the electrical energy it consumes.

This seems too good to be true, but there is no magic involved. The heat pump is not creating energy from nothing. It is harvesting existing heat energy from the outdoor air or ground and using electricity to move that heat into your home, rather than generating heat directly.

What Is SCOP?

SCOP stands for Seasonal Coefficient of Performance. While COP measures efficiency at a single specific test condition (a snapshot), SCOP gives you the average efficiency across an entire heating season, accounting for varying outdoor temperatures.

This distinction matters enormously. A heat pump's COP changes throughout the year:

On a mild autumn day at 10C outside, the COP might reach 4.5
On a typical winter day at 5C outside, the COP might be 3.5
On a bitter cold night at -5C outside, the COP might drop to 2.5

SCOP rolls all of these varying conditions into a single representative number. For UK homeowners, SCOP is a far more useful figure than peak COP because it reflects what you will actually experience over a full year.

When comparing heat pump models, always look at SCOP rather than the headline COP figure. The SCOP is calculated using a standardised European climate profile, with specific profiles for warmer, average, and colder climates. The UK falls into the "average" climate zone for SCOP calculations.

Typical COP and SCOP Values

Here are the ranges you can expect from different types of heat pump in UK conditions:

Air Source Heat Pumps

Metric	Budget Models	Mid-Range Models	Premium Models
Peak COP (at 7C/35C)	3.5-4.0	4.0-4.8	4.5-5.5
SCOP (UK climate)	2.8-3.2	3.2-3.8	3.5-4.2
Typical annual COP	2.7-3.0	3.0-3.5	3.3-4.0

Ground Source Heat Pumps

Metric	Budget Models	Mid-Range Models	Premium Models
Peak COP (at 0C/35C)	4.0-4.5	4.5-5.0	5.0-5.5
SCOP (UK climate)	3.5-4.0	4.0-4.5	4.2-4.8
Typical annual COP	3.3-3.8	3.8-4.2	4.0-4.5

Ground source heat pumps consistently achieve higher COP values because the underground temperature remains stable at around 10-12C year-round, whereas air temperatures fluctuate between -5C and 25C across the seasons.

You can compare the cost implications of these different efficiency levels using our heat pump calculator.

How to Read Manufacturer Specifications

When you look at a heat pump datasheet, you will typically see COP quoted at specific test conditions, written in a format like "COP 4.5 at A7/W35". Here is what those numbers mean:

A7/W35 means:

A7 = Air temperature of 7C (the heat source)
W35 = Water flow temperature of 35C (the heat output)

The gap between these two numbers is called the "temperature lift". The smaller the lift, the higher the COP. This is why you will see manufacturers quoting their best COP at A7/W35 (a lift of 28C) rather than at A-7/W55 (a lift of 62C), where the COP would be much lower.

Common Test Conditions to Watch For

A7/W35 - The most commonly quoted condition. Represents a mild day with low-temperature heating (underfloor heating or oversized radiators). This gives the highest COP and is the number manufacturers like to put on the front page.

A7/W55 - Same mild day but with higher flow temperature (suitable for standard radiators without upgrades). COP will be noticeably lower.

A2/W35 - A colder day (2C) with low-temperature heating. More representative of average UK winter conditions.

A-7/W35 - A very cold day. Shows how the heat pump performs during cold snaps.

When comparing models, make sure you are comparing COP figures at the same test conditions. A COP of 4.5 at A7/W35 is not necessarily better than a COP of 4.0 at A2/W35. The second figure actually indicates a more efficient heat pump because it is achieving strong performance at a more challenging condition.

The ErP Energy Label

All heat pumps sold in the UK carry an ErP (Energy-related Products) energy label, similar to those on washing machines and fridges. Heat pumps typically achieve A++ or A+++ ratings. While this confirms they are efficient, the label alone does not tell you much about relative differences between models. Always dig into the SCOP figures for meaningful comparisons.

COP vs Real-World Performance

The COP figures in manufacturer brochures are measured under controlled laboratory conditions. Your actual in-home performance will vary based on several factors.

Factors That Reduce Real-World COP

Higher flow temperatures. If your radiators need water at 50-55C rather than 35C, your COP drops significantly. Every degree of additional flow temperature costs you efficiency. This is why upgrading radiators or adding underfloor heating can improve your heat pump's performance.

Defrost cycles. Air source heat pumps need to periodically defrost their outdoor coils in cold, damp weather. During defrost, the system temporarily reverses to melt ice, consuming energy without producing useful heat. This can reduce effective COP by 5-15% during the coldest months.

Domestic hot water. Heating your hot water cylinder to 50-55C (necessary for legionella safety) requires a higher flow temperature than space heating. The COP for hot water production is typically 2.0-2.8, which pulls down the overall seasonal average.

System design and installation quality. A poorly designed system with incorrect refrigerant charge, undersized pipework, or badly positioned outdoor unit will underperform. This is why choosing an experienced MCS-certified installer is critical.

Standby and circulation pump energy. The heat pump's circulation pumps, controls, and standby power consumption are not always included in laboratory COP figures but do contribute to your real electricity bill.

Factors That Can Improve Real-World COP

Weather compensation. Automatic adjustment of flow temperature based on outdoor conditions ensures the heat pump runs at the lowest effective flow temperature at all times.

Well-insulated home. Lower heat demand means the system can operate at lower flow temperatures more of the time, boosting average COP. Check if your home is suitable for optimal performance.

Low-temperature emitters. Underfloor heating or oversized radiators allow flow temperatures of 35C or below, where heat pumps are most efficient.

Smart controls. Modern systems that learn your heating patterns and pre-heat intelligently can improve overall seasonal performance.

Why COP Matters for Your Bills

The COP directly determines your running costs. Here is a worked example showing how COP affects your annual electricity bill for heating, assuming 18,000 kWh of annual heat demand and an electricity rate of 24.5p per kWh:

SCOP	Electricity Used	Annual Heating Cost	Cost per kWh of Heat
2.5	7,200 kWh	£1,764	9.8p
3.0	6,000 kWh	£1,470	8.2p
3.5	5,143 kWh	£1,260	7.0p
4.0	4,500 kWh	£1,103	6.1p
4.5	4,000 kWh	£980	5.4p

The difference between a SCOP of 3.0 and 4.0 is £367 per year. Over a 20-year heat pump lifespan, that is £7,340. This illustrates why it can be worth investing in a slightly more expensive heat pump with a higher SCOP, or spending money on insulation and low-temperature emitters to help a mid-range heat pump achieve better real-world efficiency.

For context on how these figures compare to gas heating, see our heat pump vs gas boiler guide.

How to Monitor Your Heat Pump's COP

Once your heat pump is installed, you can track its actual COP to ensure it is performing as expected.

Heat meter data. Under the BUS grant requirements, a heat meter is fitted during installation. This measures the total heat output. Combined with your electricity meter readings (or a dedicated sub-meter for the heat pump), you can calculate your actual COP: heat output divided by electricity input.

Manufacturer apps. Most modern heat pumps come with smartphone apps that display real-time and historical COP data. Brands like Vaillant, Mitsubishi, Daikin, and Samsung all offer monitoring platforms.

Heat Geek and community data. Websites like Heat Geek publish real-world performance data from thousands of UK heat pump installations, giving you benchmarks to compare against.

If your measured COP is consistently below 2.5 for an air source heat pump, something may be wrong with the system design, settings, or installation. Contact your installer for a review.

COP and the BUS Grant

The Boiler Upgrade Scheme does not set a minimum COP requirement directly, but it does require MCS-certified installation. MCS standards mandate proper system design including heat loss calculations and emitter sizing, which naturally leads to systems that achieve reasonable COP values.

Additionally, the requirement for a heat meter means your actual performance is measured, creating accountability for installation quality.

Frequently Asked Questions

What is a good COP for a heat pump in the UK?

For an air source heat pump in UK conditions, an SCOP of 3.0 or above is considered good, and 3.5 or above is excellent. For a ground source heat pump, aim for an SCOP of 3.8 or above. Remember that real-world COP depends heavily on your specific installation, particularly the flow temperature and how well your home is insulated.

Does COP change in winter?

Yes. For air source heat pumps, COP drops as outdoor temperatures fall because the heat pump has to work harder to extract heat from colder air. On a typical UK winter day at 2-5C, the COP might be 2.8-3.5. On a very cold day at -5C, it could drop to 2.0-2.8. Ground source heat pumps are less affected because underground temperatures remain relatively constant year-round.

Is a heat pump with a higher COP always the better choice?

Not necessarily. A higher COP generally means lower running costs, but you also need to consider the purchase price, noise levels, reliability, warranty terms, and suitability for your specific property. A heat pump with a SCOP of 3.8 that costs £3,000 more than one with a SCOP of 3.3 would take over 8 years to recoup that premium through energy savings alone. Your installer can help you find the right balance for your budget and situation.

Sources

Energy Saving Trust - Heat pump efficiency - guidance on COP and seasonal performance
MCS - Heat pump standards - installation standards including heat meter requirements
OFGEM - Energy pricing - current electricity tariff rates
GOV.UK - Boiler Upgrade Scheme - grant conditions and heat meter requirements
European Commission - ErP energy labelling - energy label standards for heat pumps

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