What is an air source heat pump and how do they work?

An air source heat pump

Air source heat pumps are just one form of energy efficient heating options that have attracted a lot of attention recently. They promise both to lower your energy bills and deliver environmental benefits to boot.

While the government has now softened its stance slightly on phasing out the installation of all gas boilers by 2035 – there is a new exemption to help those who would struggle to switch to alternatives – it’s still very committed to the rollout of heat pumps. To help, it’s increased grants to install heat pumps or biomass boilers by 50% to at least £7,500 under the Boiler Upgrade Scheme.

We take a look below at how air source heat pumps work and whether they could help you save money on your energy bills – also see what is a ground source heat pump? for how they differ.

And if you’re thinking about switching supplier for a better tariff, we’ve rounded up all you need to know about finding the best gas and electricity deals and looked at what will happen to energy prices in the coming year

What is an air source heat pump?

Air source heat pumps are an energy efficient replacement for existing gas boilers. They could help you save money on your energy bills, while also making use of natural heat and therefore protecting the environment.

Air source heat pumps may also be referred to as air-to-water source heat pumps. As the name suggests, they make use of the heat in the air to heat your home and your water.

How do air source heat pumps work?

Air source heat pumps convert heat from the air outside into heat within your property.

A pump is installed outside your home, and it absorbs the heat from outside into a thermal fluid. This fluid is compressed, which increases the temperature further, and is used to heat the radiators within your home or your hot water tank.

It doesn’t need to be noticeably warm for an air source heat pump to work. It can extract heat from outside temperatures as low as -15 degrees according to the Energy Saving Trust.

Find out the ideal room temperature for inside your home.

How much do air source heat pumps cost?

Air source heat pumps will involve a significant initial outlay.

According to the Energy Saving Trust, having an air source heat pump installed will tend to cost around £14,000, so it’s not something that should be taken on without careful consideration.

Given that cost it’s important to approach a range of different installers in order to get quotes, so you can make a more informed decision.

There is also some financial support available from the government which can help you cover the cost of installation.

The Boiler Upgrade Scheme offers grants for households who are willing to upgrade their traditional boiler to a new energy efficient option with grants of up to £7,500 now available. 

A boiler upgraded to use with an air source heat pump

Find out other ways you can get help with your energy bills including ways of making your property more energy efficient, and any hardship funds which may be available.

Also find out if you qualify for the Warm Home Discount, Cold Weather Payments and Winter Fuel Payments.

Plus to reduce your usage, check out our energy saving tips.

Can an air source heat pump save me money?

Air source heat pumps can be an efficient way of heating your home, which can mean lower energy bills than if you stick with a gas boiler. Essentially they produce more units of energy than they use.

The amount of money they could save you will vary depending on your household and your typical energy use, however.

Here’s what the potential savings available look like, according to the Energy Saving Trust, based on how you currently heat your home.

Existing heating system

Potential annual saving through using an air source heat pump

Old (G Rated) gas boiler


New (A Rated) gas boiler


Old electric storage heaters


New electric storage heaters


Old (G rated) oil boiler


New (A Rated) oil boiler


Old (G Rated) LPG boiler


New (A Rated) LPG boiler




Source: Energy Saving Trust

As well as the financial savings, having an air source heat pump will also mean tangible reductions to your carbon dioxide emissions. Depending on your existing heating system you could cut your emissions by up to 7,500 kg per year.

How much space do I need for an air source heat pump?

You’ll need some space outside your property to install the air source heat pump. The pump will need to have space around it too, so that air can flow freely.

Air source heat pumps come in two main forms, and the version you go for will influence how much space is required. A monobloc system has all of the components in a single outdoor unit. These tend to be cheaper and won’t take up as much space within your home as it’s all outside.

By contrast a split system divides components between indoor and outdoor units. A split system will rely on you having space both inside and outside the home, whereas with a monobloc you only need room for the pump outside.

Generally installing an air source heat pump is classed as a permitted development, and so you don’t need to get planning permission for it.

Is an air source heat pump suitable for my property?

You’ll need adequate space outside your home ‒ and potentially inside too ‒ in order for an air source heat pump to work for you.

It’s not just a question of space though, but your heating needs too. Heat pumps tend to produce heat at a lower temperature than conventional central heating systems. This means that in order to truly get the benefit you will need to have better insulation and distribute heat over a great area, perhaps through underfloor heating, rather than relying on smaller radiators.

Heat pumps are best for homes where there are gradual temperature demands rather than sudden ones, according to the Centre for Sustainable Energy.

How long will an air source heat pump last?

If you’re spending thousands of pounds on having an air source heat pump installed, then you’ll want to feel confident that it will last for a lengthy period.

The Energy Saving Trust reckons that with regular scheduled maintenance heat pumps should last for around 15 years. Typical checks during maintenance tend to include a visual inspection of the pump, the fittings and electronics. 

The installer should be able to provide details of what checks are necessary, including what is required under the terms of your warranty.

How is an air source heat pump different from a ground source heat pump?

An alternative to an air source heat pump is a ground source heat pump, which can also help you keep your home warm more efficiently.

Ground source heat pumps involve installing pipes into the land outside your property, either through the digging of trenches or inserted into a borehole. These pipes again use a thermal fluid, but this time it takes the heat from under the ground outside your home, with that liquid then run through the heat pump and used to heat your home.

An important difference here is the cost. Ground source heat pumps tend to be far more expensive to install, since they involve the underground pipes ‒ you are looking at an outlay of between £28,000 and £49,000 depending on the method of installation you opt for. There is also the need to have access to that land outside the property, and the potential disruption that comes from having the pipes installed.

However, ground source heat pumps may be more efficient. The Energy Savings Trust notes that the temperature below the ground never drops below freezing, unlike air temperatures. As a result ground source heat pumps don’t have to work quite so hard.

Keep your house warm for less