How a heat pump can cool your home

Most UK homes are designed to keep the heat in rather than out, and very few have air conditioning. While many of us enjoy the warm weather when a heatwave hits, our homes can quickly become uncomfortably warm, stuffy and much too hot for sleeping.

It's an issue that's becoming more frequent. All the top 10 warmest years on record, according to mean temperature, have occurred since 2000. In July 2022, a new all-time temperature record of 40.3°C was set – the first time it has exceeded 40°C in the UK since records began.

Keeping our homes cool in summer as well as warm in winter – and using low-carbon methods to do so – is something more and more people are considering. 

So how can you keep cool in the heat of the summer? Despite its name, a heat pump could be the answer.

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Heat pumps that also provide air conditioning

The most obvious type of heat pump for cooling your home is called an air-to-air heat pump. These are different to the air-to-water heat pumps that are predominantly being installed into UK homes. 

They're popular in mainland Europe, where the climate is warmer, and they can be used for cooling as well as heating.

In theory, there is little difference between an air conditioning system and an air-to-air heat pump. If they are reversible, they can provide heating or cooling from the same unit – but not all do this.

Units that only have a cooling function are known as air conditioners, while those that both heat and cool the air are more commonly known as air-to-air heat pumps.

In winter, they take heat energy from the outside air and use it to heat up air that is then circulated around your home; in summer, the process is reversed to take heat from inside your home and expel it outside, thus reducing the indoor temperature – similar to the process that happens inside your fridge.

This is a different setup to a typical UK 'wet' central heating system. Heat is moved in the form of hot (or cold) air around your home using ducts, rather than as hot water in pipes that feed into radiators. 

Air is delivered into each room via wall-mounted, floor-standing or concealed units. One outdoor air-to-air heat pump unit can be connected to up to five indoor units. 

For concealed units – for example, in the ceiling – you’ll need to install ducts to circulate the air around your home. Otherwise, you might choose to have a separate outdoor unit for specific rooms (similar to the way separate air conditioning units are often installed for each room in hotter countries).

That means you're more likely to consider this type of heating and cooling system if you have a small home or flat with relatively few rooms. It might be particularly worth considering if your home often overheats in warm weather. If you're already using electric heating methods rather than a wet piped system, the switch would be more straightforward. You'll also see lower running costs than with other types of electric heating. 

Read more: how heat pumps work and air source heat pumps explained

Why choose an air-to-air heat pump?

Air-to-air heat pumps are cheaper to buy and install than air-to-water heat pumps. According to the Energy Saving Trust, it costs around £1,900 to install a system to heat a single room, or around £3,700 to heat a three-bedroom semi-detached house.

Unlike hydronic heat pumps, they are not yet eligible for a grant through the Boiler Upgrade Scheme; however, the government is currently consulting on changes to the scheme and is considering their future inclusion.

An air-to-air system is a good alternative to other types of electric heating (storage heaters or electric panels) and could be a good choice for flats where an air-to-water system isn't feasible. If you don’t already have a ‘wet’ system (pipework and radiators) installed, an air-to-air heat pump can be installed with minimal disruption.

They are much more efficient to run than a direct electric heating system (such as electric panel radiators or storage heaters). They have a similar Seasonal Coefficient of Performance (SCOP) to hydronic heat pumps – around 3 to 4. That means you should see lower running costs in the winter months than with other electric heating options. 

You only need one external heat pump unit for up to five internal units (ie five rooms), so if you need to heat (and cool) a relatively small space, an air-to-air system could fit the bill.

Some air-to-air systems can be connected to a domestic hot water tank to provide your hot water, although not all do this. If your hot water is already provided by separate means such as an electric immersion heater or point-of-use water heaters, you don’t need to replace this. If you don't, you'll need to factor in the installation of a new water heating system.

Case study: Hear from a Which? member who installed an air-to-air heat pump in a top-floor London flat.

Can all heat pumps cool your home?

The most popular type of heat pump in the UK is a hydronic air-to-water heat pump. These usually heat your home by circulating hot water through radiators and/or underfloor heating.

Although commonly used as a home heating system, to replace gas and oil boilers, hydronic heat pumps can also sometimes provide cooling by reversing the process of transferring heat from one place to another.

Not all hydronic heat pumps can do this, so if you are interested in a system that also provides cooling, discuss this with your heat pump installer when you are getting quotes, and check the specifications carefully before choosing a heat pump system. 

You’ll also need the right sort of emitters to make the most of cooling via an air-to-water heat pump system:

• Heat pump convectors: Replacing standard radiators, heat pump convectors look similar to electric panel radiators and can be floorstanding or wall-mounted. They have a built-in fan that draws air from the room across a heat exchanger, cooling (or heating) the room as required. 
• Underfloor heating: A heat pump can pass chilled water through underfloor piping to cool the floor. This absorbs heat from the air, thus reducing the temperature of the room. However, careful design is needed to prevent the formation of condensation on the floor, and this may not be the ideal choice for you if you dislike having a cold floor in your home. 

If you're considering a heat pump for your home, head to our guide to heat pumps vs. boilers for the full lowdown. Plus, find out how to reduce the upfront costs and maximise your energy bill savings in our guide to air source heat pump costs and savings.

If you're looking for a quick fix and aren't ready for a new heating system, read our guide to electric fans and portable air cons: Should you buy an air conditioner or an electric fan this summer?