A Complete Guide To Air Source Heat Pumps

Thinking about installing an air-source heat pump? Find out all you need to know about this low-carbon heating alternative.

Already decided on an air source heat pump?

How does an air source heat pump work?

An air-source heat pump works much like a fridge operating in reverse to heat your home. Here's how it works:

Outside air is blown over a network of tubes filled with a refrigerant. This warms up the refrigerant, and it turns from a liquid into a gas.

This gas passes through a compressor, which increases the pressure. Compression also adds more heat – similar to how the air hose warms up when you top up the air pressure in your tires.

The compressed, hot gases pass into a heat exchanger, surrounded by cool air or water. The refrigerant transfers its heat to this cool air or water, making it warm. And this is circulated around your home to provide heating and hot water. Meanwhile, the refrigerant condenses back into a cool liquid and starts the cycle all over again!

Heat pumps can also be a great source of hot water – but the water will be cooler than from a boiler. Practically this means that If you’re running a bath, you’ll need more hot water and less from the cold tap. So you’ll likely need a bigger hot water tank to cover your needs too.

Using an air source heat pump at home

Air source heat pumps can be used to heat up your home and water. Here are some things to consider.

Using an air source heat pump for heating

Heat pumps work best when there’s less of a difference between the inside and outside temperatures. In much the same way that your fridge has to work harder in hot weather. This makes them a good match for underfloor heating systems. Floors cover a much bigger area than radiators so they don’t need to get as hot to provide the same amount of heat. Air source heat pumps also have a lower output than gas or oil-fired boiler. This means they can’t deliver heat as quickly. Instead, they’re best used to heat your home up slowly over a longer period.

Air source heat pump and radiators

If you have radiators in your home, and you’re switching from a gas-fired heating system to an air source heat pump, you’ll probably need to buy some bigger radiators to keep your house toasty.

Using an air source heat pump for hot water

Heat pumps can also be a great source of hot water – but the water will be cooler than from a boiler. Practically this means that If you’re running a bath, you’ll need more hot water and less from the cold tap. So you’ll likely need a bigger hot water tank to cover your needs too.

Are there different types of air source heat pumps?

Yes! There are two main types of air-source heat pumps, 'air-to-air' and 'air-to-water'. Most air source heat pump installations in the UK are what’s known as ‘air-to-water’ types.

'Air-to-water' air source heat pumps

Most air source heat pump installations in the UK are what’s known as ‘air-to-water’ types. In these systems, the heat is transferred into a conventional ‘wet’ heating system. And this set-up gives you hot water and central heating.

'Air-to-air air' source heat pumps

A minority of UK air source heat pumps are ‘air to air. And, as their name suggests, these transfer the heat into the air, which is distributed around the home. They don’t provide hot water, though.

There is also a hybrid air source heat pump which can often be combined with an existing central heating system and boiler. In these hybrid air-source heat pump systems, the heat pump provides a ‘base load’ for the day-to-day heating and hot water. With the boiler only firing up to provide hotter water. Or a quick heat boost during a particularly cold snap.