The short answer
A wall-mounted indoor unit usually goes high on a wall with clear space around it, where its airflow can reach the whole room without blowing straight at people. The best spot also depends on the route for the pipes and where the condensate can drain.
On this page
The position of the indoor unit shapes how comfortable the room feels, how much of the installation you see, and how easy the unit is to look after. The ideal spot for airflow isn't always practical for pipework, so the final choice is usually a balance between the two, agreed with the installer before any holes are drilled.
What a good position looks like
| Look for | Avoid |
|---|---|
| High on a wall, with a clear gap above | Shelves, beams or cupboards crowding it |
| Air blowing across the room | Air blowing straight at a bed, desk or sofa |
| A short route to an outside wall | Long pipe runs through finished rooms |
| Room to open the front panel | A spot you can't reach to clean the filters |
| Nothing below that water could damage | Directly above a television or computer |
| Away from other heat sources | Right above a radiator or in strong sun |
Installation manuals set minimum clearances above and to the sides of the unit, so the air can get in, and installers work to those.
Airflow and comfort
Wall units are fitted high because the air they blow out spreads best from there. In cooling, the louvres send cool air out across the room, and because cool air sinks, it settles through the space. In heating, they angle down to push warm air towards the floor.
- Blow along the room. A unit on a short wall, blowing along the length of the room, usually spreads air better than one blowing across a narrow room into the wall opposite.
- Keep the air off people. A unit on the wall facing the bed tends to blow straight at you. One on a side wall, or above the head of the bed, sends air across the room instead, though above the bed puts the fan closer to your head.
- Leave the path clear. Curtains, tall furniture or a beam just in front of the unit can block the air or send it straight back into the unit.
- Watch for false readings. The unit's temperature sensor usually reads the air as it's drawn into the unit. A radiator underneath, strong sun on the unit or a nearby cooker can make it think the room is warmer than it is.
Directing the airflow explains how to set the louvres once the unit is in.
The route for pipes, cable and drain
The indoor unit connects to the outdoor unit through two refrigerant pipes, a cable and a condensate drain, which usually run together. On most wall units they can leave from the left, the right or straight out of the back.
- An outside wall is simplest. The pipes can go straight through the wall behind or beside the unit, keeping the visible run short.
- An inside wall means a longer route, usually in trunking along walls or through ceiling and floor spaces, which takes more time and shows more.
- Pipe length has limits. Many small systems are pre-charged with refrigerant for a set length, often somewhere between 5 and 15 metres depending on the model. Longer runs need refrigerant added on site, and every model has maximum length and height limits. Refrigerant pipework explained covers the detail.
- The drain needs a route. Water from the indoor unit drains by gravity where possible, so a spot with a downhill route outside or to a waste pipe is easiest. Otherwise a small condensate pump is fitted, which can add a little noise. See condensate drainage.
The indoor and outdoor positions are chosen together. The spot that's best inside may lead to a poor place outside, such as under a neighbour's bedroom window, and where the outdoor unit can go explains what limits that side.
When a wall unit doesn't fit
Some rooms don't have a good high wall. Loft rooms with sloping ceilings, rooms with large windows on every wall and walls taken up by fitted furniture can all make a wall-mounted unit awkward.
The alternatives include floor-standing console units, which sit low on the wall, and ceiling cassettes or ducted systems where there's a ceiling or loft space to hide them in. Each has its own trade-offs in cost, disruption and what's needed above or behind the ceiling.
Planning the spot
Before installation day, it helps to:
- stand in the room and picture where the air will go, and where you sit or sleep
- mark the proposed spot with tape so you can see it in place
- check what's on the other side of the wall, both indoors and outside
- mention anything hidden in the wall, such as pipes or cables you know about
- ask the installer to show you where the pipes will run and what will be visible
Plasterboard walls and some older walls need suitable fixings for the bracket, and a good installer will check the wall before choosing the final position.
Related guides
- Where the outdoor unit can goAn outdoor unit needs a firm fixing, free airflow, service access and somewhere for defrost water to drain. On a house in England it can usually go on a wall, the ground or a flat roof without planning permission if set conditions are met.
- Refrigerant pipework explainedTwo insulated copper pipes carry refrigerant between the indoor and outdoor units. They are joined at each unit, tested for leaks and cleared of air before use, and their length and route affect how the job looks and whether extra refrigerant is needed.
- Directing the airflowPoint the airflow level or slightly up when cooling, because cool air sinks, and down when heating, because warm air rises. Avoid aiming it straight at people, and use swing if the air isn't reaching the whole room.
- Where the water goes: condensate drainageWater that condenses in the indoor unit as it cools runs through a drain hose to a suitable outlet, with a small pump where it can't fall naturally. In heating mode the outdoor unit produces water too.