What are air source heat pumps?

What is an air source heat pump?

An air source heat pump is a low-carbon way to heat your home. It sits outside your property and absorbs natural heat from the air, which it then uses to warm your rooms and your hot water cylinder. They look a bit like standard air conditioning units and come in different sizes based on how much heat your household needs.

A common misunderstanding is that heat pumps generate their own electricity. They do not. Instead, they use a small amount of electricity from your supplier to extract and move heat from the outside air into your home. Using solar panels can reduce the emissions associated with its electricity use. A renewable electricity tariff can support renewable generation, but it does not make the system completely carbon-free. Unlike burning gas, oil, or wood, an air source heat pump produces no carbon emissions on site.

Because they run on electricity, which currently costs more per unit than gas, a heat pump will not automatically slash your energy bills. However, because they are so efficient, they use far less energy overall. Switching to one can reduce your exposure to volatile fossil fuel prices and, if you no longer need a gas supply, allow you to avoid the gas standing charge while helping to future-proof your home.^[1]

How does an air source heat pump work?

The technology inside a heat pump is very similar to the system used in your kitchen fridge, just working in reverse. Instead of pushing heat out to keep the inside cold, it pulls heat in from the outside to keep your house warm.

The process happens in a continuous cycle. First, the unit draws in outside air and passes it over a network of tubes filled with a special refrigerant fluid. This fluid has a very low boiling point, meaning it turns into a gas even when the outside air is cold. A compressor then squeezes this gas. When you compress a gas, its temperature rises significantly. This concentrated heat is then passed through a heat exchanger into your home's central heating system and hot water cylinder. Finally, the gas cools back down into a liquid, and the cycle starts again.

One of the biggest worries people have is whether a heat pump works in the middle of winter. The reality is that modern air source heat pumps can extract useful heat from the air even when temperatures drop to -15°C or lower. While they have to work slightly harder in freezing weather, they are designed to cope with harsh winters.

The main reason heat pumps are so popular is their efficiency. A brand-new gas boiler is usually around 90% to 95% efficient, meaning it turns most of the gas into heat but loses a little bit in the process. An air source heat pump operates at roughly 300% to 400% efficiency. This means that for every 1 unit of electricity it uses to run the compressor, it gathers 3 to 4 units of heat from the outside air. You get much more energy out than you put in.

Types of air source heat pumps

There are two main types of air source heat pump available in the UK. They both extract heat from the outside air in exactly the same way, but they distribute that heat around your home differently. The right choice depends on your current heating setup and what you want the system to do.

Air-to-water heat pumps

Air-to-water systems are the most common models used in the UK. They take heat from the outside air and feed it into a wet central heating system. This means the hot water travels through pipes to your radiators or underfloor heating, just like a traditional gas boiler system. They also connect to a hot water cylinder to provide the hot water for your taps, baths, and showers.

Air-to-air heat pumps

Air-to-air systems take heat from the outside and blow it directly into your rooms through wall-mounted fans, rather than using water and radiators. As well as heating your home in winter, many of these systems can operate in reverse during the summer, acting as air conditioning to cool your house down. The main drawback is that an air-to-air heat pump cannot heat water, so you will need a separate system, such as an electric immersion heater, for your hot water.

Is your home suitable for an air source heat pump?

Not every home is immediately ready for a heat pump. Because they work differently from gas or oil boilers, you need to check a few practical details before going ahead with an installation.

The flow temperature is the biggest practical difference. A standard gas boiler sends water to your radiators at around 65°C to 70°C, which makes the radiators hot to the touch and heats a room quickly. A heat pump works best when it sends water at around 35°C to 45°C. To get the same amount of heat into the room at a lower temperature, the heat needs a larger surface area to escape from. This is why underfloor heating works so well with heat pumps, and why installers often recommend swapping your existing radiators for larger ones.

Planning permission rules have also changed to make installations easier. In most cases, installing a heat pump falls under Permitted Development, meaning you do not need to apply for full planning permission. In England, the strict rule that required the pump to be at least one metre from your property boundary was scrapped on 29 May 2025. To qualify for Permitted Development, your installation must pass a strict noise assessment known as MCS 020a. For installations under England's Permitted Development right, MCS 020a is the required sound calculation and noise limit. If you live in a listed building or a conservation area, stricter rules still apply, and you will usually need specific consent from your local authority.^[1]

Installation costs and government grants

Installing an air source heat pump is a major investment. In 2026, the average cost of a full installation in the UK is roughly £12,000 to £12,500. Depending on the size of your property, the complexity of the plumbing, and whether you need to upgrade your radiators or hot water cylinder, quotes typically range from around £7,000 to £15,000 before any grants are applied. Ground source heat pumps cost significantly more because they require extensive digging or boreholes in your garden.

To help with these upfront costs, the government offers financial support. The old Renewable Heat Incentive scheme closed in 2022, and the current support system in England and Wales is the Boiler Upgrade Scheme (BUS), which is administered by Ofgem and has government funding allocated through March 2030. This scheme provides a one-off grant that is deducted directly from your installer's quote, meaning you do not have to pay the full amount upfront and wait for a refund.

Once the system is installed, your annual running costs will depend entirely on how well-insulated your home is and how much heating you use. Typical running costs range from £855 to £1,700 a year. Because electricity is more expensive per unit than gas, a heat pump must run efficiently to save you money on your bills. If your home is draughty, the pump will have to work harder, and your electricity bills will rise. However, a well-designed and well-controlled system can cost less to run than a typical gas boiler, particularly on a heat-pump time-of-use tariff. Savings compared with oil or direct electric heating also depend on your tariff, system design and how you use it.

The advantages and disadvantages

Switching your heating system is a big decision. It helps to weigh up the practical benefits against the drawbacks before you commit.

What happens during the installation?

Fitting an air source heat pump is more complex than simply swapping a gas boiler for a new one. It usually takes a few days, and you will experience some disruption to your heating and hot water while the work takes place. Use a qualified installer. To claim a Boiler Upgrade Scheme grant, your installer must be MCS-certified for the technology being installed.

Maintenance and lifespan

Once installed, air source heat pumps require very little day-to-day maintenance. They do not burn fuel, so there is no soot or ash to clean out, and they are generally very reliable. Most units come with a warranty lasting between five and ten years, and a well-maintained heat pump has a typical lifespan of around 15 years.

To keep the system running efficiently, you just need to keep the outdoor unit clear. Check it occasionally to make sure leaves, dust, or garden debris are not blocking the airflow around the fans. If the fan blades look dirty, you can turn the unit off and wipe them down. The manufacturer will also recommend an annual service by a qualified engineer. They will check the electrical connections, clean the internal filters and coils, and ensure the refrigerant fluid is at the correct pressure before winter sets in.