Wall-mounted air conditioning
A wall-mounted split is the most common type of air conditioning in UK homes. An indoor unit fixed high on a wall delivers conditioned air into the room, linked by slim pipework to an outdoor unit (the condenser) mounted outside. Most are reverse-cycle, so the same system cools in summer and heats in winter.
How it works
A wall-mounted split uses a refrigerant cycle to move heat. The outdoor unit holds the compressor; the indoor unit holds the evaporator and the fan you see. In cooling mode it absorbs heat from the room and releases it outside; in heating mode it runs in reverse, drawing warmth from the outside air even when it’s cold — which is what makes it an air-to-air heat pump. The two units are joined by insulated refrigerant pipes and a condensate drain. Most use inverter compressors for efficient, steady running. For the full picture, see how air conditioning works.
Pros and cons
Pros: lowest-cost fixed system; quick to install; quiet; efficient with inverter control; heats as well as cools; a huge choice of models.
Cons: the indoor unit is visible on the wall; one unit generally serves one room (several rooms need multiple heads or a multi-split); an outdoor unit must be sited somewhere acceptable, which may need planning consideration (see planning permission).
Best for / not ideal for
Ideal when you want to cool and heat one or two rooms affordably and don’t mind a visible indoor unit. Less ideal if you want a concealed or whole-home solution (look at ducted) or have nowhere acceptable to put an outdoor unit.
Typical capacities and sizing
As a rough guide, a 2.5 kW (≈ 9,000 BTU) unit suits a typical bedroom, while a large lounge may want 3.5–5.0 kW. Room size is only the start — sun, glazing and occupancy all shift it. Use the sizing tool for an estimate.
What it costs
Wall-mounted splits are the most affordable fixed option, and a single-split for one room is the cheapest way in — around £1,500–£3,000 supplied and fitted as a 2026 guide price. A multi-split covering 2–4 rooms is more like £3,000–£6,000+. Cost rises with capacity, with multi-split arrangements, and with anything that makes installation harder (long pipe runs, awkward access). See the full home cost guide for current prices and what moves them.
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