Most people think of a split system as air conditioning, and in July that is what it is. For the other nine months it is a heat pump: the same outdoor unit pulls warmth out of the outside air and the indoor unit blows it into the room. Because it is moving heat rather than making it, a good unit delivers three to five units of heat for every unit of electricity it uses.
That makes it a very cheap way to heat a single room, and a much cheaper project than replacing a boiler. There are no radiators to change, no hot water cylinder and no pipework through the house — just a small hole through one wall to the outdoor unit.
Where it makes the most sense
- Loft conversions and extensions the central heating doesn't reach, or reaches badly. Top-floor rooms are also the ones that overheat in summer, so you get both.
- Garden offices and studios where running a gas supply is impossible and electric heaters are expensive.
- Conservatories and orangeries that are freezing in winter and unusable in a heatwave.
- The rooms you actually use. Heating the living room with a heat pump and turning the boiler down can cut what you spend on gas.
What it won't do
An air-to-air heat pump heats air in the rooms it's fitted in. It doesn't heat water, so it won't replace a boiler on its own, and it isn't covered by the government's Boiler Upgrade Scheme grant. If you want to take the boiler out entirely you need an air-to-water heat pump from an MCS certified installer — that's not something we fit, and we'd rather tell you here than at quote stage.
Still deciding between heating first or cooling first? It's the same unit. Our air conditioning pages cover the summer side.
Questions
Common questions
What is an air-to-air heat pump?
It's a split system — an indoor unit on the wall and an outdoor unit outside — that moves heat from the outside air into the room in winter, and out of the room in summer. Most people know it as air conditioning. Every modern split system we fit is a heat pump, which is why one unit does both jobs.
Is an air-to-air heat pump the same as air conditioning?
Yes, in practice. The same unit cools in summer and heats in winter. People call it air conditioning when they're thinking about summer and a heat pump when they're thinking about heating bills.
Can an air-to-air heat pump replace my gas boiler?
Usually not on its own, because it heats rooms but doesn't make hot water or feed radiators. It works best alongside your existing heating — taking over the rooms you use most, or heating a loft, extension or garden office that the central heating doesn't reach. We don't install air-to-water heat pumps, the type that replaces a boiler.
Is there a government grant for air-to-air heat pumps?
No. The Boiler Upgrade Scheme only covers air-to-water heat pumps that replace a fossil-fuel heating system, and it has to be claimed through an MCS certified installer. Air-to-air systems are not eligible, whoever fits them. The upside is that they cost a fraction of an air-to-water system to install.
Do they work when it's cold?
Yes. Modern units keep heating well below freezing outside, and the better models are rated down to around −15°C to −20°C. They become less efficient as it gets colder, which is why sizing the unit to the room properly matters more than the brand.