Wall-mounted air conditioning

How a wall-mounted split works

A wall-mounted split system has two parts. The indoor unit sits high on a wall, takes in the room’s air, passes it over a coil and blows it back out cooler or warmer. The outdoor unit holds the compressor and a second coil, and either gives the room’s heat to the outside air or, in heating mode, takes heat from it. The two are joined by a pair of insulated refrigerant pipes, a power and control cable and a condensate drain, usually through one neat hole in the wall.

Because they run as heat pumps, most modern wall-mounted units heat as efficiently as they cool. Many people who fit one for summer end up using it on cold mornings in spring and autumn too.

Where wall-mounted units suit

• Bedrooms that are too hot to sleep in, especially under the roof.
• Living rooms and kitchen-diners with large windows or glazed extensions.
• Home offices and garden rooms where computers and sun add heat all day.
• Small offices, shops, salons and treatment rooms where one unit can serve the whole space.
• Loft conversions that overheat in summer.

If you want several rooms done, a multi-split system can run them from one outdoor unit. If you want no visible unit in the room, look at ducted or, in suspended ceilings, cassette units.

Choosing the position

Where the indoor unit goes makes a big difference to comfort. It needs space above and around it for air to circulate, a clear throw across the room, and a route for the pipework and drain. In a bedroom, we avoid blowing air straight at the bed. In a living room, we aim the air along the room rather than at the sofa. We also think about how the unit looks, and most brands offer slim, quiet or designer models for rooms where appearance matters.

The outdoor unit needs airflow, a firm base or wall bracket and a position that keeps noise away from bedrooms, yours and the neighbours’. Our guide to where to put the outdoor unit goes into the detail. Where the drain can’t fall naturally to the outside, we fit a condensate pump.

Sizing and efficiency

Wall-mounted units come in a range of outputs. The right one depends on the room’s size, the glazing and which way it faces, the insulation and how the room is used. A unit that is too small struggles on the hottest days. One that is too big cycles on and off and is less comfortable. We size each unit on the survey and explain the output we have chosen.

Look at the seasonal efficiency figures, SEER for cooling and SCOP for heating, on the manufacturer’s data. Higher figures mean less electricity for the same result. Our article on SCOP, SEER and energy labels explains how to read them.

Noise and the neighbours

Indoor units are designed to be quiet, and manufacturers publish sound levels for each model and fan speed, so it is worth comparing them for a bedroom or study. The outdoor unit is usually the bigger question. It makes some noise when the compressor and fan are running, so we place it away from bedroom windows where we can, on anti-vibration mounts, and where it has room to breathe. If the property is in a flat, a terrace or close to neighbours, we talk the position through with you on the survey, along with any consent you may need from a landlord or managing agent.

Refrigerant and the rules

From 2025, new single split systems containing less than 3 kg of refrigerant can’t use F gases with a global warming potential above 750 (GOV.UK: F-gas bans). That is why new wall-mounted units use refrigerants such as R32, which has a global warming potential of 675. Fitting any split system means working on a refrigerant circuit, which must be done by a certified company with qualified engineers. AirCon Doctor is an F-Gas certified company.

Installation day

A single wall-mounted system is usually fitted in a day. The engineer fixes the indoor unit bracket, drills the hole for the pipework, mounts the outdoor unit, runs and insulates the pipes, connects the drain and the cable and finishes the pipework neatly, in trunking where it runs on the outside wall. The refrigerant circuit is pressure tested and evacuated before the refrigerant is released, then the system is commissioned in cooling and heating. Most systems need their own electrical supply, and as NICEIC approved contractors we can install and certify the circuit. Our guide to installation day explains each step.

Price, VAT and warranty

A single-room wall-mounted system is typically £1,200–£2,200 + VAT, including supply, installation, commissioning and F-Gas documentation. Pipe length, access to the outdoor unit position, a condensate pump, a new circuit and premium indoor units all affect the price. HMRC zero-rates energy-saving materials installed in homes until 31 March 2027, and says most air conditioning units are air source heat pumps, but each case depends on the facts, so we confirm the VAT on your quote (HMRC Notice 708/6). Warranty is the manufacturer’s, on its terms. Daikin’s standard warranty on split air conditioning, for example, is 2 years (Daikin UK warranty).