Installation Advice
What Is an Indoor Unit on an External Wall?
This is one of the most misunderstood phrases in air conditioning surveys. Here's exactly what it means, and what it doesn't.
Installation image to be uploaded by WDI Group.
Alt text: Air conditioning indoor unit mounted inside a room on an external wall
A common source of confusion
When we talk about fitting an indoor unit on an external wall, some customers understandably wonder if that means the unit itself will be outside. It doesn't. The indoor unit is always installed inside the room, on the wall itself, and stays indoors just like a radiator or a picture frame.
What the phrase actually refers to is which wall of the room the unit is mounted on, and specifically whether that wall has open air directly on its other side.
What 'external wall' means in this context
An external wall is simply a wall that forms part of the outside envelope of the building, as opposed to an internal partition wall between two rooms inside the house. If you knocked a hole straight through an external wall, you'd come out into the garden, the street, or open air rather than into another room.
This matters for air conditioning because the indoor unit needs pipework, cabling and usually a condensate drain to connect through to the outdoor unit, and the most direct, tidy route for that is straight through the wall behind the indoor unit.
Why this position is preferred
Mounting the indoor unit on an external wall allows a short, direct core hole straight through to the outside, where the pipework can then run a short distance to the outdoor unit. This keeps pipe runs neat, minimises the amount of pipework hidden in lofts or run through multiple rooms, and reduces the number of joints in the refrigerant circuit.
It also generally makes for a tidier finished job, since there's less pipework visible inside the property and less need for boxing-in through internal rooms.
What happens on internal walls instead
When an indoor unit has to be positioned on an internal wall, perhaps because that's the best location for cooling the room, the pipework then needs a longer route to reach the outside, often through a loft space, a service void, or along skirting and up through an external wall elsewhere in the property.
This is entirely possible and something we do regularly, it just means more planning around the pipe route and usually a bit more pipework to conceal.
The indoor unit itself never sits outdoors
To be absolutely clear: regardless of which wall it's fixed to, the indoor unit is always inside the room, blowing conditioned air into that space. It is not weatherproofed and could not function or survive outside. The unit that sits outdoors is a separate piece of equipment, the outdoor condenser unit.
The two units are connected by insulated refrigerant pipework, electrical cabling, and usually a condensate drain, which is what needs to pass through the wall, not the indoor unit itself.
How this affects your survey
During a survey, we'll usually explain which wall in the room we recommend for the indoor unit and why, including whether it's an external or internal wall and what that means for the pipe route to the outdoor unit.
If you have a strong preference for the unit's position based on furniture layout or where you spend most time in the room, let us know, and we'll explain what's achievable and any effect it has on pipe routing.