A heat pump is a heating system that uses electricity to move heat from outside air, ground or water into a building.
Unlike a gas boiler, which creates heat by burning fuel inside the home, a heat pump transfers heat. This is why a well-designed heat pump system can deliver more heat energy than the electrical energy it uses.
How a heat pump works
A heat pump absorbs heat from outside and raises it to a useful temperature for heating and hot water. It can still work when the outside air feels cold because there is still heat energy available to extract.
The system uses electricity to run components such as the compressor, pumps and controls. The relationship between electricity used and heat delivered is often described using a coefficient of performance.
coefficient of performance =
heat output ÷ electricity input
For example, a heat pump delivering 3kWh of heat from 1kWh of electricity has a coefficient of performance of 3. Real-world performance changes with weather, system design and heating demand.
Common types of heat pump
The two most common domestic options are air source heat pumps and ground source heat pumps.
| Type | How it collects heat | Typical consideration |
|---|---|---|
| Air source heat pump | Takes heat from outside air. | Usually easier to install than ground source. |
| Ground source heat pump | Takes heat from the ground through buried pipework. | Can be efficient but needs suitable outdoor space and more installation work. |
| Water source heat pump | Takes heat from a suitable water source. | Less common and depends on site conditions. |
Heat pump vs boiler
A boiler and a heat pump both heat a home, but they work differently. A boiler converts fuel into heat. A heat pump transfers heat from outside into the home.
| Feature | Boiler | Heat pump |
|---|---|---|
| Energy source | Usually gas, oil, LPG or electricity. | Electricity. |
| How it heats | Creates heat directly. | Moves heat from outside. |
| Best system conditions | Can run at higher flow temperatures. | Usually works best at lower flow temperatures. |
| Key home factor | Boiler efficiency and controls. | Heat loss, radiators, flow temperature and design. |
Heat pump efficiency and COP
Heat pump efficiency is often explained using coefficient of performance, or COP. A COP of 3 means the system delivers three units of heat for each unit of electricity used.
Seasonal performance is usually more useful than a single best-case COP because the system must work across colder and warmer periods. Lower heating flow temperatures and good design usually help performance.
What affects heat pump running costs?
Heat pump running costs depend on the electricity unit rate, the system’s efficiency and the amount of heat the home needs.
Electricity price
A higher electricity unit rate increases running cost for each kWh used.
COP / seasonal performance
Better performance means more heat for each unit of electricity.
Insulation and heat loss
Loft insulation and other heat-loss improvements can reduce demand.
Radiators and flow temperature
Correct system design can help the heat pump run more efficiently.
What makes a home suitable for a heat pump?
Heat pumps can work in many types of homes, but the design matters. A good survey should look at heat loss, insulation, radiator sizes, hot-water needs, outdoor unit location and existing heating controls.
- Lower heat loss through insulation and draught reduction.
- Suitable radiator or underfloor heating capacity.
- Space for an outdoor unit or ground loop where relevant.
- Clear hot-water and household heating requirements.
- Accurate heat-loss calculation rather than a rough guess.
- Installer experience with low-temperature heating design.
Should you insulate before installing a heat pump?
Often, it is sensible to check insulation and draughts before replacing a heating system. Reducing heat loss can lower the heat demand the heat pump needs to meet.
This does not mean every home needs to become perfect before a heat pump is possible. It means heat-loss improvements can make sizing, comfort and running costs easier to manage.
Compare upgrade order
Use insulation and heating calculators to compare payback before choosing what to do first.
Heat pump grants and upfront cost
Heat pumps usually cost more upfront than a like-for-like boiler replacement. UK grant schemes may reduce the cost for eligible homes, but rules, eligibility and grant levels can change.
Before relying on a grant, check the current scheme rules, installer requirements and whether the quote separates equipment, labour, survey work and any radiator or hot-water-cylinder changes.
Heat pumps and EPC rating
A heat pump can affect a property’s EPC rating, but the result depends on the property, heating fuel, electricity assumptions, insulation and the certificate method used.
EPC impact should not be the only reason to install a heat pump. Comfort, running costs, carbon reduction, suitability and installation quality matter too.
Common heat pump mistakes
- Comparing only installation cost and ignoring running cost assumptions.
- Not checking heat loss before sizing the system.
- Assuming existing radiators are always suitable.
- Running the system like a high-temperature boiler.
- Ignoring hot-water cylinder and space requirements.
- Not comparing insulation, boiler replacement and heat pump options together.
- Focusing only on COP rather than whole-system design.
What to check before choosing a heat pump
- Full heat-loss calculation.
- Air source, ground source or other system type.
- Expected seasonal efficiency, not just best-case COP.
- Radiator, pipework and hot-water-cylinder requirements.
- Outdoor unit location, noise and access.
- Installation cost after any grant assumptions.
- Expected running cost using your electricity tariff.
- Installer credentials, warranty and aftercare.
FAQs
What is a heat pump?
A heat pump is a heating system that uses electricity to move heat from outside air, ground or water into a home.
Does a heat pump work in cold weather?
Yes, heat pumps can work in cold weather, but performance depends on system design, weather conditions and home heat demand.
Is a heat pump cheaper to run than a boiler?
It depends on electricity and gas prices, heat pump efficiency, home insulation, heating demand and system design.
Do I need insulation before a heat pump?
Not always, but reducing heat loss can improve comfort, sizing and running-cost performance.