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Wall mounted air conditioning
Wall mounted air conditioning is a split system: a slim unit high on the wall inside, linked by two small pipes to a quiet unit outside. It cools in summer and heats in winter. Apex fits wall units for bedrooms, living rooms, home offices and small businesses across Dartford, Kent and south-east London, usually in a day per room.
How it works
A wall unit does not make cold air. It moves heat. In summer it takes heat out of the room and releases it outside. In winter it runs in reverse and brings heat in.
Refrigerant carries the heat between the indoor unit and the outdoor unit. An inverter compressor speeds up to reach your set temperature, then slows right down to hold it, which is why modern units are quiet and cheap to run once the room is comfortable.
Because it heats as well as cools, a wall split is really an air-to-air heat pump. Used for heating, it can take the chill off a cold room in minutes, without waiting for the boiler.
Usually by gravity, through the same hole as the pipes, to a gully or downpipe outside. Where the drain cannot fall, for example on an inside wall, we fit a small, quiet condensate pump. A blocked drain is the most common reason a wall unit drips, so we check it at every service.
Is it right for you?
Sizing
Wall units are sold by output in kilowatts (kW). The right size depends on the room's heat gain, not just its floor area: which way it faces, how much glass it has, the insulation, the people and the equipment in it.
As a rough guide from our own jobs, small and medium bedrooms and home offices often need 2.0kW to 2.5kW. Larger bedrooms, garden rooms and lounges often need 3.5kW. Big living rooms and kitchen-diners often need 5kW or more. In one Bexley home we fitted a 2.5kW unit in the bedroom and a 5kW unit in the living room.
The building regulations say comfort cooling should be sized from a heat-gain calculation and should not be more than 120% of the cooling the room needs (Approved Document L). An oversized unit switches on and off, wastes energy and does a poor job of drying the air. An undersized one runs flat out and never quite gets there.
Noise
Indoors, quieter than most people expect. On low fan, many current wall units are rated at around 19 to 21 dB(A), about the level of a whisper. On high fan, during a heatwave, you will hear a soft rush of air.
Outside, the noise that matters is at your neighbour's window. For permitted development on a house, the outdoor unit must pass the MCS 020(a) calculation: 37 dB(A) at 1m from a neighbour's nearest door or window to a habitable room. We run that check before we fit, choose the quietest workable spot and use anti-vibration mounts.
If your bedroom is small, ask about a unit with a "quiet" or "night" mode, which caps the fan and the compressor speed.
Your options
People often search for a wall mounted air conditioner without an outdoor unit. They exist, but they are a compromise. Here is how the three types compare.
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| Type | Outside | Noise in the room | Heating | Best for |
|---|---|---|---|---|
| Wall split (indoor + outdoor unit) | Outdoor unit on the ground or a bracket, one small hole | Very low: the compressor is outside | Yes, efficiently | Almost every home and small business |
| All-in-one (through-wall) | Two grilles on the outside wall, no outdoor unit | Higher: the compressor is in the room | Yes, on most models | Places where an outdoor unit is not allowed |
| Portable | A hose out of a window | High | Rarely | A stopgap, not a fitted system |
We have fitted an all‑in‑one unit where an outdoor condenser was not an option. For most rooms, though, a split system is quieter, more efficient and better at heating. Living in a flat? See air conditioning in a flat for the consent your lease may need.
Cost
Which? (July 2026) put a typical one-room air-to-air system at about £1,900 fitted. Prices across London and the south-east tend to sit higher than the national average. We give you a fixed written quote after a free survey. These are the things that move the price:
Once a room is at temperature, an inverter wall unit often draws roughly 0.5kW to 1kW. At the Ofgem price cap for October to December 2026 (26.32p per kWh), that is roughly 13p to 26p an hour. Heating in deep winter uses more.
Our guides explain both sides in full: what air conditioning costs to buy and fit and what it costs to run. Ready to go ahead? Read how our air conditioning installation works, from survey to handover.
A photo is often enough for a first idea of what will work.
Ranges we fit
Ranges we fit include these. Makers update their models often, so we recommend the current one that suits your room and budget at the survey.
Wall-mounted · Premium wall unit · Daikin
Heating and cooling plus humidifying, dehumidifying, fresh-air ventilation and air purification in one unit.
Wall-mounted · Design wall unit · Daikin
A slim, curved unit designed to look good on a living-room wall.
Wall-mounted · Compact design unit · Daikin
Function and looks balanced in a compact unit, available in several finishes including a dark wood effect.
Wall-mounted · Commercial wall unit · Daikin
A lightweight, flat-fronted wall unit often used with Daikin's commercial outdoor units.
Wall-mounted · Design wall unit · Mitsubishi Electric
A slim, stylish unit in white, silver or black with very low noise levels.
Wall-mounted · Mid-range wall unit · Mitsubishi Electric
A compact white unit with Wi-Fi as standard and lower-impact R32 refrigerant.
Wall-mounted · Entry wall unit · Mitsubishi Electric
A slim, compact unit for bedrooms and small rooms.
Wall-mounted · Commercial wall unit · Mitsubishi Electric
A flat-panel Mr Slim wall unit for offices and shops, with flexible controls.
Wall-mounted · Premium wall unit · Panasonic
Panasonic's flagship wall unit with nanoe X air cleaning, built-in Wi-Fi and a choice of white, silver or graphite.
Wall-mounted · Compact wall unit · Panasonic
A compact unit for smaller rooms, with built-in Wi-Fi and R32 refrigerant.
Wall-mounted · Standard wall unit · Panasonic
A quiet, compact standard-range unit that still packs a punch, ideal for garden rooms and bedrooms.
Real Apex jobs
Reviews
Olly and his colleague have installed an air conditioner in my bedroom last month. They have been very polite and professional. Olly has answered all of my questions and provided multiple quotes. I was worried that the outside unit of the AC system would be loud, however it turned out to be surprisingly quiet. I'm very pleased with that. The AC system works well and cools the room very quickly, I have had no issues with it.
Olly and Lee worked very tidily and were extremely careful about dust capture while drilling in the house. External work was hampered by plants and water butts but was all taken in their stride. Very pleased with end result. Nice neat job. Would highly recommend.
Compare
Low on the wall, ideal for lofts and replacing radiators.
Find out moreEven airflow for offices, shops and open-plan rooms.
Find out moreHidden in the ceiling, only the grilles show.
Find out moreRoom-by-room temperature control for ducted systems.
Find out moreDaikin, Mitsubishi Electric and Panasonic.
Find out moreQuestions
Yes, for most rooms they are the simplest and most efficient choice. A modern inverter wall unit cools a bedroom in minutes, heats it in winter as an air-to-air heat pump, and runs quietly. The main downside is that it is on show. If you want nothing on the walls, a ducted system hides the unit in the ceiling or loft.
Many split systems run for 10 to 15 years, and often longer, when they are serviced every year. Clean filters and coils, a clear drain and correct refrigerant charge all reduce wear on the compressor. Units that run flat out because they were sized too small tend to age faster. If yours is older and failing, our repair or replace guide helps you decide.
Yes. Rinse or vacuum the filters every few weeks when the unit is in heavy use. Once a year it needs a proper service: coil and fan clean, drain check, electrical checks and a performance test. Most manufacturers also expect a yearly service to keep the warranty valid. Our air con servicing covers all of this.
Yes. A multi-split runs two to five indoor units from one outdoor unit, so the outside wall stays tidier. The rooms share the outdoor unit's capacity, and if it fails, every room is affected. Separate single splits cost a little more but each room works on its own. We explain both options at the survey.
On a house in England, a unit that heats as well as cools is usually permitted development, as long as the outdoor unit meets the size and siting rules and passes the MCS 020(a) noise check. Cooling-only units, listed buildings, flats and some conservation-area walls need more. See our planning permission guide.
Usually around 2m up, with a small gap below the ceiling so the unit can draw air back in. We place it so the air reaches the whole room without blowing straight onto the bed, the sofa or a desk, and where the pipes can take a short, neat route outside.
Talk to Olly directly. He quotes and fits the jobs himself.
Quickest way to a price: send on WhatsApp
Free survey and a fixed written quote for new systems. No obligation.
