Air source heat pumps: how do they work and are they effective in the UK?

Air source heat pumps. They’ve been a hot topic in the UK for several years, frequently making the news as coverage of our collective push towards net zero intensifies. But – much like trigonometry and wine tasting – there are plenty of people out there nodding along to the conversation without actually knowing how it all works – and there’s no shame in that! We’re here to simplify air source heat pumps (ASHPs) for you and give you all the information you need to decide whether they’re worthwhile (spoiler: we think they are).

How do air source heat pumps work?

Air source heat pumps take heat energy from outside and increase it to a higher temperature, sending it into your wet central heating system (air to water heat pumps) or feeding it into the home through fans (air to air heat pumps). They use the same kind of technology as an air conditioner, but in the opposite direction. Essentially, heat from outside is blown over a ‘heat exchange surface’ (on the external part of the heat pump), which causes the refrigerant liquid inside to evaporate (i.e. turn into a gas). This is then moved through a compressor, increasing its temperature. This heat is transferred into the heating system, providing heating and hot water. Once the gas has transferred its heat, it cools down and becomes liquid again, returning to the beginning of the cycle.

What are the benefits of air source heat pumps?

Air source heat pumps have an important role to play in the transition to net zero. According to the National Audit Office, heating homes across the UK accounted for 18% of our greenhouse gas emissions in 2021 (the most recent year for which data are available). While some households have gone electric, many still use gas to heat their homes, which is less eco-friendly and inferior when it comes to energy-efficiency – for every unit of gas it takes to heat a home with a boiler, heat pumps use three to four times less energy! Analysis by Nesta suggests that each installation of a heat pump cuts home gas use by at least 70%, saving households money and making them less reliant on fluctuating wholesale gas costs.

Are air source heat pumps effective in cold climates?

A survey carried out by Electrify Research demonstrated the misconception that heat pumps are unable to warm homes during the winter months, with 40% of Brits surveyed saying they believed this. But in Europe, the main countries leading the way then it comes to air source heat pump adoption are Finland, Norway and Sweden, which are notoriously cold! Air Source Heat Pumps can still secure heat from the air even when the temperature is as low as -15°C! During periods when the temperature dips to -6°C, running costs may rise to just above those of a gas boiler, but only during these periods. Otherwise, they are more attractive from both a financial and efficiency standpoint.

Are air source heat pumps suitable for property types?

There is a common belief that ASHPs are only suitable for new builds, but this is not necessarily the case. The Energy Systems Catapult (ESC), an independent research and technology organisation, ran a project to test the feasibility of installing heat pumps in existing British homes. It found that properties including Victorian terraces and 1960s flats could have a heat pump successfully installed. In a report published in 2022, ESC said: “The suggestion that there are particular home archetypes in Britain that are unsuitable for heat pumps is not supported by project experience and data.” Ultimately, air source heat pumps are most effective in buildings that are well-insulated – and it pays to have an energy-efficient home, shaving hundreds of pounds off household energy bills.

There are some considerations to take into account when it comes to space, as some equipment will be placed both inside and outside of the home, with the main unit sitting outside, but your installer should cover these considerations with you when assessing your home’s suitability and specific requirements. Air source heat pumps can be mounted to the ground or installed on a wall or flat roof, and permission is not usually required unless you live in a conservation area or area of outstanding national beauty. Most installations can be carried out in just a couple of days.

Is there any support to help me install an air source heat pump?

While the UK has been slow to adopt ASHP technology than other nations, the MSC Foundation, which oversees the MCS standards scheme, reported that, in 2023, there was a nearly 20% jump in certified heat pump installations compared to the previous year. Some of this growth is down to the availability of government schemes, including the Boiler Upgrade Scheme grant (BUS) which offers grants of up to £7,500 towards the cost and installation of air source or ground source heat pumps. The scheme is open to homeowners (or small business property owners) in England and Wales if they have a fossil fuel heating system or an electric system without a heat pump. The Social Housing Decarbonisation Fund (SHDF), which helps local authorities and social housing landlords to deliver home energy efficiency upgrades, also funds the installation of heat pumps – at no cost to tenants.

The benefits of air source heat pumps are clear – from reduced carbon emissions and improved EPC ratings to lower energy bills (with potential savings of up to £1,090 per year) – but the UK’s uptake of this technology has been slower than other countries, even those with much lower average temperatures. Thankfully, this trend is starting to show signs of change, with a notable increase in the number of installations in recent years. At Thrift, our expert Air Source Heat Pump installers can talk you through the process, going over any concerns you might have and even helping you find funding opportunities. You can read more about air source heat pumps here or get in touch with our team today by calling 0800 689 3415.

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