Air Source Heat Pump Efficiency: UK Guide 2026
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: how efficient is an air source heat pump?
A good air source heat pump can provide roughly 2.5–4 units of heat for each unit of electricity it uses, depending on conditions. This is expressed as a Coefficient of Performance, or COP. A COP of 3 means 1 kWh of electricity produces 3 kWh of useful heat.
Seasonal figures are more useful for annual performance. The final Energy Systems Catapult Electrification of Heat trial measured a median whole-system Seasonal Performance Factor of 2.78 across 428 air source heat pumps. Meanwhile, Energy Saving Trust’s current heat-pump guidance uses an SPF of around 3.1 as a typical figure. Efficient installations can exceed this, but results vary by home and system.
Air Source Heat Pump Efficiency: How Efficient Are Heat Pumps in the UK?
Air source heat pumps can be remarkably efficient. In normal operation, they can deliver around three units of heat for every unit of electricity they use, and well-designed systems can do better. However, that does not mean every installation runs at “300% efficiency” all year. Performance changes with outdoor temperature, heating-water temperature, hot-water demand, system design and controls.
For UK homeowners, the most useful question is not the maximum efficiency on a brochure. It is: how efficiently will the whole system heat this particular home across a full year?
This guide explains air source heat pump efficiency in practical terms, including COP, SCOP, real-world UK performance, winter operation and the factors that make the biggest difference.
Considering a heat pump? Compare free quotes for your property and ask for the expected seasonal performance before choosing a system.
Air source heat pump efficiency at a glance
| 2-bedroom property | Typical cost before BUS | £7,500 BUS grant | Potential homeowner cost |
|---|---|---|---|
| Straightforward small terrace or heat-pump-ready home | £7,500–£9,500 | -£7,500 | £0–£2,000 |
| Typical 2-bed terrace or semi | £9,000–£11,500 | -£7,500 | £1,500–£4,000 |
| More complex retrofit | £11,500–£12,500+ | -£7,500 | £4,000–£5,000+ |
SCOP is formally based on performance across a defined heating season, while measured SPF can use broader system boundaries that include additional electrical consumption.
Why can a heat pump be more than 100% efficient?
A heat pump uses electricity mainly to move heat rather than create it.
In an air-to-water system, refrigerant absorbs heat from outdoor air. A compressor raises its pressure and temperature, then a heat exchanger transfers that energy into water for radiators, underfloor heating and a hot-water cylinder. The refrigerant cools and repeats the cycle.
This is why a heat pump with a COP of 3 can deliver 3 kWh of heat while using about 1 kWh of electricity. The extra energy comes from the outside air.
For the deeper explanation of the evaporator, compressor, condenser and expansion valve, read how air source heat pumps work.
COP, SCOP and SPF: which figure matters most?
COP is a snapshot. It shows the ratio of heat output to electricity input at a specific operating point. COP can be high in mild weather with low-temperature heating water, then fall on a freezing day.
SCOP, or Seasonal Coefficient of Performance, estimates performance across a heating season under standardised test conditions. It is therefore more useful than peak COP when comparing models.
SPF, or Seasonal Performance Factor, is commonly used for measured in-home performance. Depending on the measurement boundary, it can include electricity used by pumps, immersion heaters and other system components. The Electrification of Heat project, for example, reported both narrower SPFH2 and wider SPFH4 measurements.
Therefore, do not compare a laboratory COP of 5 with a monitored whole-system SPF of 2.8 as though they are the same measure.
What efficiency do air source heat pumps achieve in real UK homes?
The Department for Energy Security and Net Zero-funded Electrification of Heat Demonstration Project provides one of the largest UK datasets. Its final 2024 analysis included 428 air source heat pumps and reported a median SPFH4 of 2.78, with a mean of 2.81.
The SPFH4 boundary includes electricity used by the heat pump and relevant heating-system components, so it is more demanding than a compressor-only COP. The project also found considerable variation between installations.
You can explore the final Electrification of Heat reports and datasets.
That is the key buying lesson: air source heat pump efficiency is a property-and-system outcome, not simply a product specification.
Are air source heat pumps efficient in winter?
Yes, but efficiency usually falls as the outside temperature drops.
Energy Systems Catapult’s final data found a median whole-system COP of 2.57 at 0°C, falling to around 2.30 at -5°C across the monitored air source heat pumps.
On the coldest monitored day for each property, the mean outdoor temperature was -4.15°C and the median whole-system COP was 2.27. The systems were therefore still delivering more than twice as much heat as the electrical energy they consumed.
The more important design question is whether the selected model can meet the home’s calculated heat loss at the local winter design temperature.
Why flow temperature has such a big effect
Flow temperature is the temperature of the water leaving the heat pump for the heating system. Lower flow temperatures generally improve efficiency because the compressor has less work to do.
The Electrification of Heat study found a statistically significant relationship between higher mean flow temperature and lower seasonal efficiency.
MCS heat-pump guidance makes the underlying principle clear too: efficiency improves when the heat source is warmer and the required heating-water temperature is lower.
Larger radiators or underfloor heating can help because they provide more surface area. That allows rooms to receive enough heat without very hot water.
Not every property needs new radiators, though. A room-by-room heat-loss calculation should show which existing emitters are suitable. See the air source heat pump temperature guide for more detail.
How do hot water and defrost cycles affect efficiency?
Domestic hot water usually needs a higher temperature than space heating, so the heat pump may run less efficiently while heating the cylinder. Some systems also use an immersion heater periodically, which can increase electrical consumption.
Defrosting is normal too. In cold, damp weather, moisture can freeze on the outdoor coil. The heat pump temporarily uses energy to clear the frost so efficient heat transfer can resume. Existing Getfreequote guidance also explains that visible water or vapour during defrost can be completely normal.
A defrost cycle does not mean the unit is faulty. However, frequent defrosting, unnecessary immersion-heater use or very high hot-water settings can reduce seasonal performance.
What affects real-world efficiency most?
The main factors are flow temperature, outdoor temperature, correct system sizing, radiator or underfloor-heating capacity, controls, hot-water settings, auxiliary-heater use and the home’s heat demand.
Insulation needs a careful explanation. It does not directly change the heat pump’s thermodynamic COP. However, reducing heat loss can make it easier to heat the home at a lower flow temperature and reduces the total amount of heat the system must provide.
MCS guidance stresses that heat-pump sizing should start with a room-by-room heat-loss assessment that considers building fabric, room dimensions, ventilation and local winter conditions.
Does higher efficiency always mean lower running costs?
Higher efficiency reduces the electricity needed for a given amount of heat, but it does not guarantee the lowest bill.
Running cost depends on the home’s heat demand, the heat pump’s seasonal efficiency and the electricity tariff. For example, a home needing 12,000 kWh of useful heat with an SPF of 3 would require roughly 4,000 kWh of electricity for that heating demand, before allowing for differences in measurement boundaries.
Energy Saving Trust notes that electricity costs considerably more per unit than gas. That is why a heat pump can be several times more energy-efficient than a gas boiler without automatically being several times cheaper to run. A strong installation achieving a higher SPF improves the economics significantly.
For the financial side, see the air source heat pump running-cost guide and the air source heat pump versus gas boiler comparison.
How to improve air source heat pump efficiency
- Use the lowest practical flow temperature. Weather compensation can automatically adjust it as outdoor conditions change.
- Keep indoor temperatures reasonably steady. Heat pumps often work best maintaining comfort rather than repeatedly reheating a cold house.
- Use suitable radiators or underfloor heating. Adequate emitter size supports lower flow temperatures.
- Avoid unnecessarily high hot-water settings. Follow manufacturer and installer guidance for comfort and hygiene.
- Limit avoidable immersion-heater use. Direct electric backup is useful when required but is less efficient than normal heat-pump operation.
- Reduce heat loss where practical. Fabric improvements reduce the amount of heat the system must provide.
- Monitor performance. Investigate unexpected increases in electricity use or falling efficiency.
Energy Saving Trust similarly recommends steady operation, appropriate heating curves and lower flow temperatures where the heating system allows them.
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: how efficient are air source heat pumps?
Air source heat pumps are highly efficient because they move heat rather than producing all of it from electricity. In UK homes, a sensible expectation is several units of heat for each unit of electricity, but the exact figure depends on the measurement method and installation.
Real-world UK evidence shows that whole-system seasonal performance can be lower than brochure COP figures, especially once hot water, pumps and winter operation are included. Good results come from low practical flow temperatures, correct sizing, suitable emitters and well-configured controls.
When comparing quotes, ask for the proposed design flow temperature, room-by-room heat loss and expected seasonal performance. Those figures tell you more than a single headline COP.
Ready to compare options? Get a free, no-obligation quote based on your property and heating needs.
