Air-to-air heat pumps

Most UK homes use radiators to heat each room. Because they have water flowing through them, it’s called ‘wet’ central heating. One advantage of air-to-air heat pumps is that they don’t need a wet central heating system to warm your home.  

They usually have one unit outside and at least one unit inside. These use pipes carrying a refrigerant between the units. The indoor unit is usually high on a wall inside the room, as close to the external unit as possible. This ensures there’s less pipework inside your home.  

The one outdoor unit can connect to more inside units but will need more pipework installed. Typically, these pipes run in a slim plastic channel around the upper edges of the room. 

It’s the same setup as air conditioning, which is more common in hotter climates. You can configure these units for cooling as well as heating. 

All in one systems

This is also known as a monobloc system. It’s relatively new and an advantage is that it doesn’t need any outside unit at all – all components are in a single indoor unit. These systems connect to the outside air through two small ducts that pass through an external wall:  

• One duct draws in outside air to extract heat from it. 
• The other duct removes the cooled air. 

The ducts need only two holes about 15-20cm wide, making them much less visually intrusive than the outdoor unit of other types.  

Ducted systems 

Ducted systems are ventilation systems that you typically see in energy efficient houses such as ‘Passivhauses’. Some types of ducted systems are also known as exhaust air heat pumps, and can also supply hot water. 

Ducted systems may not be suitable for older or larger houses with high heating needs, though. 

The ducts move air around the house through pipes that are slim enough to be hidden inside the ceiling voids. The heat pump warms the air in an air handling unit, which is roughly the size of a boiler. These units normally go in a loft or utility room. 

Suitable for smaller homes 

Air-to-air heat pumps can be a good choice for smaller homes and flats, especially where an air-to-water heat pump wouldn’t suit. Their outdoor units are typically smaller than air-to-water heat pumps. This smaller size can make them a good choice for small flats and homes with less, or no, outdoor space. 

The monobloc system could be suitable for homes where external installation is challenging due to limited access or planning restrictions. 

Can be used for cooling 

They can provide cooling during warm weather. However, you should first consider passive cooling methods like window shades and improved ventilation to minimise energy use. If your home overheats in summer despite these measures, speak to your installer about setting your heat pump for cooling as well. This lets you to keep comfortable temperatures all year round while managing your energy costs.  

Improve your carbon footprint

Unlike gas and oil boilers, they’re a low carbon heating system that takes heat from the outside air. This will improve your home’s carbon footprint. 

• Indoor units can be noisier than other heat pumps. 
• They normally need new pipework installing when installing multiple indoor units. 
• They don’t blow fresh air into the room – instead they recirculate the existing air. You’ll still need to ventilate the house just as you would with other types of central heating. 

More often, air-to-air sytems are installed in smaller properties, such as flats and park homes. 

Elsewhere in Europe, they’re are more common. This is partly because of the warmer climate, where they’re useful for cooling as well as heating. 

There are a few questions you should ask yourself before you decide if an it’s right for you: 

Most types will need an area outside your home for a unit to fit to a wall or on the ground near the house. It needs space around it to get a good flow of air. 

Most air-to-air systems don’t provide hot water, so you’ll need another way of heating water for showering, bathing and hot taps. Consider the amount of hot water your household needs, as well as any space or budget considerations. Alternative options include: 

• A hot water cylinder with an electric immersion heater. 
• An electric shower or ‘point of use’ water heaters. 
• A type of air-to-air heat pump model that does provide hot water to heat a hot water cylinder. There’s at least one manufacturer producing these now. 
• Solar water heating, if you have enough space to install the solar hot water panels. You’ll need a suitable hot water cylinder, and you’ll need an electric immersion to provide enough hot water when there’s less sunshine. 

Our research shows that air-to-air heat pumps can cost around:

• £1,900 to heat a single room
• £3,700 to heat a three-bedroom semi-detached house

There may also be other costs to consider, such as redecoration.

Unlike air source and ground source heat pumps, there are no government grant schemes to install air-to-air systems. But they’re a much more affordable option if you live in a smaller home, or a flat.

There’s currently not much data on how air-to-air systems perform in the UK, so it’s difficult to know how much money you’d save. 

How much you could save depends on: 

• What heating system you’re replacing. 
• How the heat pump system is designed.
• How efficiently you’re using it.

Ask your installer for an indication of running costs based on their design of the system for your home.

We recommend getting quotes from at least three different installers who are certified with the Microgeneration Certification Scheme (MCS). You can use their tool to find installers near you.

Getting multiple quotes ensures you’re getting the best value for your money. 

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