Yes, and most modern units do
A modern split air conditioner can heat your home because it is a reversible heat pump. In summer it moves heat out of the room. In winter it reverses the refrigerant cycle and moves heat from the outside air into the room. The same indoor and outdoor units do both jobs, so there is nothing extra to buy.
This is why these systems are also called air-to-air heat pumps. The Energy Saving Trust describes them as a low carbon way to heat a home, with the limit that they don't provide hot water. An air-to-water heat pump, the kind that feeds radiators and a hot water cylinder, works on the same principle but delivers the heat into water.
How it works when it is cold outside
Outdoor air contains heat even when it feels cold. The outdoor unit's refrigerant is colder still, so it absorbs heat from the air. The compressor then raises the refrigerant's temperature, and the indoor unit releases that heat into the room through a fan.
As the outdoor temperature drops, there is less heat to collect and the unit has to work harder, so both output and efficiency fall. Every model has a stated operating range for heating on its data sheet. Check the lowest outdoor temperature it is rated for and its heating output at low temperatures, as well as at the standard test point.
When frost builds up on the outdoor coil, the unit runs a short defrost cycle. Heating pauses for a few minutes and you may see steam rising from the outdoor unit. That is normal. The unit also needs a drain route for the water from defrosting, which the installer should plan for.
How a Leeds winter compares
Leeds winters are cool and damp more often than severely cold. The Met Office long-term averages for the Leeds Weather Centre station, 1991 to 2020, give the monthly means for each season. Damp air near freezing is when the outdoor unit frosts most often, so expect defrost cycles on raw January mornings.
A unit sized only for summer cooling may not be the right size for winter heating, since a room's heat loss on a cold day can differ a lot from its heat gain on a hot one. Ask the installer to check the heating output at low outdoor temperatures against the room's heat loss, especially for a loft room or an extension with large windows.
Running cost in heating mode, with the sums
The efficiency of a heat pump in heating mode is given as SCOP, the seasonal coefficient of performance. A SCOP of 4.0 means that over a heating season, the unit produces an average of 4kWh of heat for each 1kWh of electricity it uses.
Ofgem's price cap for 1 October to 31 December 2026 sets average rates of 26.32p per kWh for electricity and 7.97p per kWh for gas, paid by Direct Debit.
Worked example: the cost of 1kWh of heat. From the air-to-air unit at SCOP 4.0: 26.32 / 4 = 6.6p. From a gas boiler at an assumed 90% efficiency: 7.97 / 0.9 = 8.9p. From a plug-in electric heater, which turns 1kWh of electricity into 1kWh of heat: 26.32p.
So to put 20kWh of heat into a home office over a cold week, the air-to-air unit would cost 20 x 6.6p = £1.32, the gas boiler 20 x 8.9p = £1.78, and an electric heater 20 x 26.32p = £5.26. The boiler figure also assumes you could heat only that room with it, which on a normal central heating system you can't. Running the whole system to warm one room costs more.
The SCOP of your model and your own tariff will change these figures, so do the sum with your own numbers. A unit with a SCOP of 3.5 would make heat at 26.32 / 3.5 = 7.5p per kWh, still below the gas figure.
Where it works well as heating
Air-to-air heating suits rooms that need heat at different times from the rest of the house.
- Home offices used during the day when the rest of the house is empty.
- Loft conversions and extensions that the central heating struggles to reach.
- Conservatories and garden rooms with no radiator.
- Spring and autumn, when one room is cold but the house doesn't need full heating.
- Homes on oil, LPG or electric storage heaters, where the saving per kWh is larger.
Leeds homes where it helps most
Leeds City Council's housing strategy counts about 19,500 pre-1919 back-to-back houses in the city. Many have solid walls and attic rooms that are cold in winter and hot in summer, so one unit that does both jobs is a good fit. Attic rooms and dormers in Victorian terraces across areas such as Headingley, Harehills and Armley are similar.
In villages on the edge of the district, such as Bramham or East Keswick, some homes are off the gas grid and heat with oil or LPG. Heating the most-used rooms with an air-to-air unit can mean the boiler runs less.
What the survey should check if heating matters to you
If you plan to use the unit mainly for heating, say so when you book the survey. The installer should work out the room's heat loss, which depends on the walls, windows, floor and roof. A solid stone wall in a Leeds terrace loses heat faster than an insulated cavity wall, and a loft room with little insulation loses more again. The unit's heating output at a low outdoor temperature should cover that heat loss.
The position of the outdoor unit matters more in winter. It needs space around it for air to flow, a raised stand or bracket so snow and standing water don't block it, and a drain route for the water from defrosting. A spot that drips onto a path can freeze, so plan where the water goes.
The outdoor unit still has to meet the 37 dB(A) noise limit at the nearest neighbour's habitable room window under permitted development, calculated with the MCS 020 a) method. Units can sound different in heating mode and during defrost, so ask the installer about the sound power figures in both modes.
The limits
An air-to-air unit heats the room it is in. Warm air doesn't travel well through doorways, so a unit in the lounge won't heat the bedrooms. A multi-split with an indoor unit in each room is the answer if you want several rooms heated.
It doesn't heat water. If you replace a gas boiler entirely, you still need another way to heat water, such as an electric immersion or an air-to-water heat pump with a cylinder.
Warm air heating feels different from radiators. The air near the ceiling warms first, and the fan moves it around. Some people prefer it, some don't. A floor-standing indoor unit can feel more like a radiator than a high-wall unit.
The Boiler Upgrade Scheme and air-to-air heat pumps
Since 28 April 2026, the Boiler Upgrade Scheme in England and Wales has offered a £2,500 grant towards eligible air-to-air heat pumps. The installer must be MCS certified and applies for the grant on your behalf. The home also needs a low carbon source of hot water, and the scheme is designed for replacing fossil fuel heating, so a single bedroom unit added alongside a gas boiler won't usually qualify.
Our partner installers are MCS certified. Ask at survey whether your plan meets the scheme's conditions.
The VAT rate helps separately. HMRC's VAT Notice 708/6 zero-rates the installation of air source heat pumps in homes until 31 March 2027, which includes air-to-air units. Our partner installers apply the 0% rate to domestic installations.
Getting the most heat for the least money
Set the heating to a steady temperature such as 20°C and leave it, instead of switching it off and on, since inverter units are most efficient running gently. Keep the indoor filters clean so air flows freely. Keep the outdoor unit clear of leaves, snow and anything stacked against it. Close the door of the room you are heating. Use the timer to warm the room before you need it instead of heating it from cold at full power.
Sources
Guidance is general and indicative. Always confirm details with a qualified F-Gas registered installer. Get a free quote.