The wall mounted head is the shape almost every British domestic system takes, and the reason is practical rather than aesthetic. It sits high, it throws air across the ceiling and lets it fall, it drains by gravity to an outside wall, and it can be serviced from a step ladder. Everything that goes wrong with one afterwards is a position decision taken on the day.
Where a wall air conditioner head should go
High on a wall with a clear throw across the longest dimension of the room, not blowing into a wardrobe, a curtain or a stairwell, and not directly over a bed or a desk. The unit is designed to condition a volume of air rather than to blow at a person, and a head that has been positioned for the shortest pipe run rather than for the room is the commonest regret in a domestic installation.
Why an inside wall is sometimes better
The obvious position is the outside wall nearest the outdoor unit, because it is the cheapest pipe run. It is not always the right one. A head on the far wall throwing back into the room can distribute air far better, and the extra pipe is a small share of the total. Where the outside wall is a large glazed elevation, there may be no sensible mounting point at all.
What fitting a wall mounted aircon unit actually involves
A back plate levelled and fixed, a cored hole angled slightly downward so the drain falls, insulated refrigerant pipe, a condensate drain and an interconnecting cable dressed together through the wall, and the head hung on the plate. Outside, the pipes are either in trunking or, on a considered job, chased and made good so the run is not the first thing a visitor sees.
Small rooms and small heads
Manufacturers make compact heads for bedrooms and small studies, and their appeal is as much visual as technical. The thing not to do is choose the smallest head and then ask it to serve the glazed extension it was never sized for. Pick the capacity for the room's heat gain first, then choose the smallest case in that capacity.
Questions people ask about wall mounted air conditioning unit
How high should a wall mount AC unit be fitted?
Near the ceiling with the manufacturer's stated clearance above it, so the air throw runs along the ceiling and falls back through the room. Too low and it blows across the occupants; too tight to the ceiling and it starves the intake. The installation manual sets the numbers, and a good installer follows them.
Can the pipework be hidden?
Usually, at a cost. Chasing a wall internally and making good, or running the pipe through a floor void, gives a clean result and adds labour and a plasterer. External trunking is the standard finish and is why the run is worth agreeing at survey rather than discovering afterwards.
Does the indoor head make much noise?
A modern head on low fan is quiet, and the sound most people notice is airflow rather than machinery. What is more often audible is the outdoor unit, particularly to a neighbour, which is why its position matters at least as much as the head's.
Can I move a head later?
Only by recovering the refrigerant, remaking the pipework and recommissioning, which is a certified engineer's job rather than a maintenance task. That is the practical reason to spend time on position before the first hole is cut.