Wall-Mounted Air Conditioning

A wall-mounted split system is the air conditioning most people picture. A slim indoor unit sits high on the wall, and a separate outdoor unit outside does the work of moving heat in or out. The two are joined by refrigerant pipework, a drain and a cable through one small hole in the wall. The same system cools in summer and heats in winter.

As a guide, one room typically starts from around £2,500 installed, and most single-room systems are fitted in a day.

What Is a Split Air Conditioner?

Split means the system comes in two parts. The indoor unit holds a coil and a quiet fan. The outdoor unit holds the compressor, a second coil and a larger fan. Putting the noisy, hot-running parts outside is what makes a split system quieter and more efficient than a portable unit, where everything sits in the room with you.

A single-split system has one indoor unit and one outdoor unit. A multi-split system runs several indoor units from one outdoor unit. Indoor units also come as floor-standing units, ceiling cassettes and ducted units, but for most rooms a wall unit is the simplest and most cost-effective choice.

Why a Wall Unit Suits Most Rooms

• Lower cost. A wall unit is usually the least expensive type of indoor unit to buy and fit.

• Quick to install. Most single-room systems are fitted in a day.

• Quiet. The quietest wall units are rated at around 19 dB(A) on their lowest fan setting.

• Heating and cooling. The systems we fit for homes heat as well as cool, so one unit keeps the room comfortable all year.

• Efficient. Inverter compressors slow down once the room reaches the set temperature, rather than switching on and off.

• Simple to control. A handheld remote comes as standard, and many models can also be controlled from an app.

The Drawbacks

• It is visible. A wall unit is a long, slim box high on the wall. Most people soon stop noticing it, but if you want nothing on show, a ducted system may suit you better.

• It needs the right wall. The unit needs a clear gap above and to the sides for airflow, and ideally an outside wall nearby to keep the pipe run short.

• The air comes from one point. In a long or L-shaped room, one unit may not reach every corner evenly. Two smaller units, or a cassette, can work better.

What Size Do You Need?

Most bedrooms and home offices need 2.0 to 2.5 kW, and most living rooms need around 3.5 kW. Large open-plan spaces may need 5.0 kW or more. Wall units are made in sizes from about 1.5 kW up to around 7 kW. Our guide to what size air conditioner you need explains how to work it out, and we confirm the size for each room at the survey.

Where Should the Unit Go?

• High on a wall, with the clear space above and to the sides that the manufacturer specifies.

• Where the air will not blow straight at a bed, sofa or desk.

• On or near an outside wall, so the pipework takes a short route. Where that is not possible, pipes can run through cupboards, ceiling voids or neat trunking.

• Where the drain can fall away to the outside. Where there is no natural fall, a small condensate pump is fitted.

• With a sensible position for the outdoor unit, on a wall bracket, on the ground or on a flat roof. See our guide to air conditioning outdoor units.

How Installation Works

1. Survey. We measure the room, agree positions for both units and the pipe route, and check the electrical supply.

2. The wall hole. One hole, usually about 65 mm across, is core-drilled through the wall. It slopes slightly down to the outside so water drains away.

3. Fixing the units. The indoor unit hangs on a bracket fixed to the wall. The outdoor unit goes on a bracket, a stand or a solid base.

4. Pipes and wiring. Insulated copper pipes, the drain and the cable run between the two units, in neat trunking where they are on show.

5. Electrics. The system is connected to a suitable supply with an isolator switch next to the outdoor unit.

6. Testing and commissioning. Our F-Gas certified engineers pressure test the pipework, evacuate it to remove air and moisture, release the refrigerant and check the system runs correctly. Most new systems use R32 refrigerant.

What Does It Cost?

As a guide, one room typically starts from around £2,500 and multi-room systems usually range from £5,000 to £10,000+. The price depends on the size of the unit, the length and route of the pipework, where the outdoor unit goes and the electrical work. We give you a clear written quote after a free survey. Our guide to air conditioning costs in the UK explains each factor.

Looking After a Wall Unit

Clean the filters regularly, as your manual describes, and keep the outdoor unit clear of leaves and clutter. Our guide on how to clean your air conditioner shows you how. We recommend a service every year, or twice a year if you use the system for heating. See our air conditioning servicing page.

Frequently Asked Questions

Does a wall-mounted air conditioner need an outdoor unit?

A split system does, because the outdoor unit is what gets rid of the heat. Through-wall units without a separate outdoor unit exist, but they are louder and less powerful. See air conditioning without an outdoor unit.

Can a wall unit heat a room?

Yes. The systems we fit for homes heat as well as cool, and they heat efficiently because they move heat rather than make it. Read more about air conditioning as a form of heating.

Can I fit a wall unit myself?

No. By law, work on the refrigerant circuit must be carried out by an F-Gas certified engineer. Our article on the dangers of DIY air conditioning explains the risks.

Do I need planning permission?

Usually not for a house in England, as long as the outdoor unit meets the permitted development limits. Flats, listed buildings and some conservation areas follow different rules. See our planning permission guide.

Call 01772 288651 or use the form below to book a free survey. We will measure the room, recommend the right system and give you a clear written quote.

Last updated: November 2026.