Wall-mounted air conditioners

A wall-mounted split is the default choice for cooling a single room, and the most popular home air conditioning system in the UK. One slim indoor unit fixes high on the wall; one outdoor condenser sits outside; a pair of insulated refrigerant pipes runs between them through a small core hole. An inverter compressor varies its speed to hold your set temperature efficiently, rather than switching on and off. Choose a reverse-cycle model and the same unit heats the room in winter, often more cheaply than a gas boiler.

Modern units run on R32 refrigerant, reach A+++ efficiency and are genuinely quiet indoors, from 16 to 19dB(A) on low. They need professional installation and an outdoor unit, which is the main practical difference from a portable. If an outdoor unit is not an option, jump to the no-outdoor-unit section below.

Sizing. Start at about 1kW of cooling per 10m² (our BTU calculator does the sums for your room), then insist on a heat-load calculation. An oversized unit short-cycles and dehumidifies poorly; an undersized one runs flat out. Common single-room sizes are 2.0, 2.5, 3.5, 4.2 and 5.0kW.

Efficiency and running cost. Compare SEER (cooling) and SCOP (heating) and aim for A+++. In cooling, a 2.5kW-class unit typically draws 0.3 to 0.6kW in use, about 8 to 16p an hour at the October 2026 cap rate of 26.32p/kWh. The winter upside is bigger: at SCOP 4.6, heat costs about 5.7p per kWh delivered, below the roughly 9p per kWh from a gas boiler, so a reverse-cycle split can heat a room for less than gas.

The £2,500 grant. The Boiler Upgrade Scheme air-to-air grant (England and Wales) is worth £2,500, but only for a reverse-cycle unit fitted by an MCS installer that replaces a fossil-fuel or electric heating system, not for comfort cooling alongside a gas boiler or for portables. It is now live, but the terms are detailed, so check GOV.UK for the current position before you count on it.

Prices and grant rules correct as of July 2026; running costs updated for the October to December 2026 price cap. The energy price cap changes quarterly, so check current rates before budgeting.

Every major brand sells an R32 wall-mounted split, and the differences are mostly design, quietness and top-end efficiency rather than whether they work. Designer favourites include the Daikin Stylish and Emura, Mitsubishi Electric MSZ-AY and MSZ-LN, Panasonic Etherea, Toshiba Haori with its fabric front, LG Artcool and the Samsung WindFree, which cools without a direct draught. Installed prices track the brand tier: Samsung and LG from around £1,400, Panasonic and Toshiba from around £1,600, Daikin and Mitsubishi Electric from around £1,800, all supplied and fitted for a 2.5 to 3.5kW unit.

If an outdoor condenser is not allowed, a monobloc (through-the-wall) unit keeps the compressor and coils inside the indoor box and vents through two discreet grilles in the external wall. Olimpia Splendid Unico and Powrmatic Vision are the best-known UK ranges, at roughly 1.8 to 3.6kW. They are ideal for flats, leasehold properties, listed buildings and conservation areas, and because they are sealed and pre-charged they can be fitted without an F-Gas engineer. The trade-offs are lower capacity (one medium room at most), more audible noise because the compressor is indoors, and slightly lower efficiency. This is different from a portable, which is not fixed and vents through a hose.