Heat Pump COP Explained: What It Means & Why It Matters
Check Your Eligibility for Boiler Upgrade Scheme (BUS)
Complete your details below to check your eligibility.
Thank you
We've received your details and will be in touch shortly.
Quick Answer: What Does Heat Pump COP Mean?
Heat pump COP, or Coefficient of Performance, is the ratio between useful heat output and electrical power input at a stated operating point. A COP of 3 means about 3 units of heat are supplied for every 1 unit of electricity used.
Higher is generally better, but COP must be compared at the same test conditions. For an air-to-water heat pump, A7/W35 means 7°C outdoor air and 35°C heating-water flow. The same unit may have a much lower COP in colder weather or when producing hotter water.
For yearly running-cost estimates, look at SCOP as well as COP.
What Is COP in an Air Source Heat Pump?
If you are comparing air source heat pumps, you will often see figures such as “COP 4.5” or “COP 5.0”. COP stands for Coefficient of Performance. It tells you how much useful heat a heat pump delivers compared with the electricity it uses at a specific operating condition.
A COP of 4 means the heat pump delivers 4 kW of heat for every 1 kW of electrical power it consumes at that moment. The extra energy is heat moved from the outdoor air.
COP is useful, but it is only a snapshot. Outdoor temperature, heating-water temperature, hot-water production and defrost cycles all affect performance. For annual running costs, SCOP or measured seasonal performance is more useful.
Considering an air source heat pump? Compare quotations based on a proper property survey and complete system design rather than choosing a unit from one headline efficiency figure.
What Is COP and How Is It Calculated?
The basic formula is:
COP = heat output ÷ electrical input
If a heat pump supplies 8 kW of heat while using 2 kW of electricity, its COP at that operating point is 4.
A heat pump is not creating all that heat from electricity. It uses electrical energy to run components such as the compressor, fan and pumps while transferring additional thermal energy from outside.
Energy Saving Trust and MCS best-practice guidance distinguishes instantaneous COP from seasonal measurements based on energy delivered and electricity consumed over time.
For the refrigeration-cycle mechanism, see Get Free Quote’s guide to how air source heat pumps work.
Why Can Heat Pump COP Be Higher Than 1?
A direct electric heater converts electricity into heat, so 1 kWh of electricity provides roughly 1 kWh of heat at the point of use. A heat pump works differently.
Its outdoor unit absorbs low-temperature heat from the air. Refrigerant carries that energy to a compressor, which raises its pressure and temperature. The heat then transfers into water for radiators, underfloor heating or a hot-water cylinder.
Because much of the delivered heat comes from the environment, heat output can be several times larger than electrical input.
Energy Saving Trust describes heat pumps as more than three times as efficient as gas or oil boilers in terms of energy use, although actual performance varies with the system and operating conditions.
What Do A7/W35, A2/W35 and A7/W55 Mean?
A COP number is incomplete unless you know the test conditions.
For air-to-water heat pumps, “A” refers to outdoor air temperature and “W” refers to heating-water temperature.
| Test condition | Meaning | Why it matters |
|---|---|---|
| A7/W35 | 7°C air, 35°C water | Mild-weather, low-temperature heating |
| A2/W35 | 2°C air, 35°C water | Colder weather at the same flow temperature |
| A7/W55 | 7°C air, 55°C water | Higher-temperature heating duty |
| A-7/W35 | -7°C air, 35°C water | Cold-weather performance |
Vaillant, for example, explains A7/W35 as an outdoor temperature of 7°C with the heat pump producing 35°C heating water. This illustrates why a COP figure needs its test condition attached.
When comparing two products, compare A7/W35 with A7/W35 rather than one manufacturer’s mild-weather figure with another product measured under more demanding conditions.
What Is a Good COP for an Air Source Heat Pump?
There is no single “good COP” for every situation.
A COP above 4 can be plausible for a modern air source heat pump operating in mild weather with a low flow temperature. A COP around 2.5–3 may also be reasonable when outdoor air is colder or the system must produce hotter water.
This is why a lower COP at a demanding test condition does not automatically indicate a poor heat pump.
A better buyer question is:
What COP does this heat pump achieve at the outdoor and flow temperatures relevant to my property?
Why Does Heat Pump COP Change?
Outdoor temperature
As outdoor air gets colder, the heat pump must work harder to raise the captured heat to a useful temperature.
The greater this temperature lift, the harder the compressor generally needs to work and the lower the COP becomes.
That does not mean a suitable air source heat pump stops working below zero. Modern systems can continue operating in freezing conditions, although efficiency changes.
Flow temperature
Flow temperature is one of the most important factors in heat-pump efficiency.
Heat pumps usually run more efficiently when radiators or underfloor heating can provide enough warmth using lower-temperature water.
Larger radiators, suitable underfloor heating and weather-compensating controls can therefore help reduce the required flow temperature.
For a deeper explanation, see Get Free Quote’s guide to air source heat pump temperatures.
Hot water and defrost cycles
Heating a domestic hot-water cylinder often requires hotter water than normal space heating. COP can therefore fall while the heat pump is heating the cylinder.
Cold, damp weather can also cause frost to form on the outdoor heat exchanger. The heat pump periodically runs a defrost cycle to remove it.
During defrost, some energy is used without delivering normal space heating. Defrosting is a normal part of air source heat pump operation in suitable winter conditions.
COP vs SCOP vs SPF: What Is the Difference?
These three terms are related but should not be treated as interchangeable.
COP — Coefficient of Performance: a test-point or instantaneous ratio between heat output and electrical input under specific conditions.
SCOP — Seasonal Coefficient of Performance: a standardised seasonal figure designed to represent efficiency across a range of temperatures and operating loads.
SPF — Seasonal Performance Factor: commonly used to describe measured seasonal performance from an installed system.
There is an important technical detail with SPF: the system boundary matters. One measurement may cover the heat pump alone, while another may include circulation pumps, supplementary heaters or other equipment.
Energy Saving Trust’s heat-pump best-practice guidance specifically notes that efficiency figures should identify both the operating conditions and what parts of the system are included.
For annual electricity estimates, SCOP is normally more informative than a headline COP. Once the system is installed and adequately metered, seasonal measured performance can give a clearer picture of how the actual property is performing.
How COP Affects Electricity Use
For a given amount of required heat, a higher seasonal performance figure means less electricity is needed.
Imagine a property requires 12,000 kWh of useful heat during a year.
At seasonal performance of 3:
12,000 ÷ 3 = approximately 4,000 kWh of electricity
At seasonal performance of 4:
12,000 ÷ 4 = approximately 3,000 kWh of electricity
That is a difference of about 1,000 kWh.
This simple example is why annual running-cost estimates should not be calculated from one favourable laboratory COP figure.
Get Free Quote’s air source heat pump running-cost guide covers the wider effect of heat demand, seasonal efficiency and electricity tariffs.
Does Better Insulation Increase COP?
Not directly at a fixed test condition.
A manufacturer’s A7/W35 COP does not increase simply because the heat pump is installed in a better-insulated house.
However, a lower-heat-loss property requires less heating energy and may be able to stay comfortable using lower radiator flow temperatures. That can improve seasonal system performance and reduce total electricity consumption.
This distinction matters.
MCS heat-load guidance focuses on calculating the building’s heating requirement so heating equipment can be correctly sized for the property and its design conditions.
How to Compare Heat Pump COP Figures on a Quote
When an installer or manufacturer gives you a COP figure, ask:
- At what outdoor temperature was the COP measured?
- At what flow temperature was it measured?
- What SCOP is expected for the proposed system?
- What flow temperature is the heating system designed to use in my home?
- What annual electricity consumption is predicted from my calculated heat demand?
Do not assume the heat pump with the highest headline COP will automatically have the lowest running cost.
A useful quotation should connect product performance with your heat loss, radiator sizes, hot-water requirement and controls.
A room-by-room assessment is the right starting point. Get Free Quote’s heat pump survey guide explains what should be assessed before the final design is agreed.
What Should UK Homeowners Focus on Beyond COP?
COP is useful, but it should not make the buying decision by itself.
Check whether the proposed heat pump can heat your property at a sensible flow temperature. Look at predicted seasonal performance, radiator outputs, room-by-room heat loss and hot-water requirements.
You should also make sure competing products are being compared under identical operating conditions.
A COP of 5 at A7/W35 cannot fairly be compared with a COP of 3 measured at a much more demanding operating point.
If you are still deciding whether the technology suits your property, read Get Free Quote’s guide to whether your home is suitable for a heat pump before comparing final quotations.
Get Your Free Air Source Heat Pump Quote
Find the right air source heat pump solution for your home. Tell us a few details and our team will help you explore suitable options at a competitive price.
Quick to complete. No obligation.
Get your quote
Enter your details below and one of our team will get back to you.
Frequently asked questions
Find clear answers to common questions about air source heat pump efficiency, including COP, SCOP, SPF, cold-weather performance, flow temperature, radiators, underfloor heating, insulation, defrost cycles, hot water and running costs.
A typical air source heat pump can deliver several units of heat for every unit of electricity consumed. Energy Saving Trust technical guidance gives a broad COP range of around 2.5–4, depending on operating conditions.
A COP around 3 means the heat pump is delivering three units of heat for each unit of electricity. However, one COP reading should not be used to predict annual performance because weather and flow temperatures continually change.
There is no single pass-or-fail number for every property. Energy Saving Trust currently refers to around 3.1 as typical seasonal performance, while the final Electrification of Heat field project measured a median whole-system SPFH4 of 2.78. Better-performing installations can exceed 4.
Yes, provided “300%” is understood as a COP of 3. Heat pumps can deliver more heat energy than the electricity they consume because they also collect environmental heat from outside.
In Energy Systems Catapult's final UK field data, the median whole-system COP at 0°C was about 2.57. Individual systems can perform above or below that figure.
The same study recorded a median whole-system COP of approximately 2.30 at -5°C. Cold weather reduces efficiency, but the monitored systems were still producing substantially more heat than the electricity they consumed.
Yes. Correctly selected heat pumps continue extracting heat below 0°C. Their efficiency and maximum output change with outdoor temperature, so cold-weather output must be considered during system sizing.
Higher flow temperatures require the heat pump to create a larger temperature difference between its heat source and the heating water. That makes the compressor work harder and generally reduces COP and seasonal efficiency.
Yes. Radiators work well when they can provide the room's required heat output at an efficient flow temperature. Some existing radiators may be suitable, while others may need increasing in size.
Underfloor heating can be an excellent match because its large surface area allows useful heat output at relatively low water temperatures. However, properly sized radiators can also achieve strong efficiency.
Insulation primarily reduces how much heat the property loses. It can also allow the heating system to operate at a lower flow temperature, which may improve heat-pump efficiency while reducing total energy consumption.
Defrost cycles temporarily reduce efficiency because the heat pump uses energy to remove frost from the outdoor coil. They are a normal part of cold, damp-weather operation rather than evidence of a fault.
Usually, yes. Domestic hot water generally requires higher temperatures than space heating, increasing the temperature lift the compressor must achieve.
Not automatically. Running costs also depend on electricity and gas prices, the home's heat demand and the seasonal efficiency achieved. Energy Saving Trust notes that high electricity-to-gas price differences can offset some of a heat pump's efficiency advantage.
The best method is to compare measured useful heat output with the electricity used over a meaningful period. If reliable heat metering is unavailable, monitor electricity consumption, temperatures and comfort, and ask your installer to investigate unexpectedly poor performance.
Conclusion
Heat pump COP tells you how much useful heat a heat pump delivers for each unit of electricity it uses at a specific operating point.
A higher COP usually means better efficiency, but only when figures are compared under the same conditions. Outdoor temperature and heating-water temperature can change the figure significantly.
For annual running costs, look beyond headline COP. Check the expected SCOP, proposed flow temperature, property heat loss and estimated electricity consumption.
If you are considering an air source heat pump, compare quotations based on a proper property survey and complete heating-system design rather than one specification-sheet number.
