Choosing the right size air conditioner is the most important decision you'll make. Too small and it runs flat out without catching up; too big and it cools the room without removing the humidity. Here's how the sizes work.
The four sizes
We fit four sizes of wall-mounted split unit: 2.5kW, 3.5kW, 5kW and 7kW. As a rough guide, a 2.5kW suits a bedroom or small home office, a 3.5kW suits a living room or larger bedroom, a 5kW suits a large or open-plan room, and a 7kW suits a very large room or a business premises.
The size is about the room, not the house. A small bedroom in a big house still takes a 2.5kW. We size the unit to the space it's cooling and heating.
Rough room sizes
As a general guide: a 2.5kW suits a room up to about 20m², a 3.5kW suits around 20–30m², a 5kW suits around 30–45m², and a 7kW suits around 45–65m².
These are starting points. A sunny conservatory, a room with big windows, or a kitchen with heat from cooking may need to step up a size. We confirm the right size after a look at the room.
Why too small is a problem
A unit that's too small for the room runs flat out trying to reach the set temperature. It never quite gets there, it works harder than it should, and the room never feels properly comfortable. It's also working the compressor hard, which isn't what you want.
If you're between sizes, it's usually better to step up — a slightly larger unit reaches the set temperature and then ticks over quietly, rather than running hard the whole time.
Why too big is a problem
A unit that's too big cools the room quickly but doesn't run long enough to remove the humidity. The result is a room that's cold but clammy — not comfortable. Oversizing also means short, frequent cycles that aren't as efficient.
The right size runs long enough on a hot day to cool and dehumidify the room properly, then settles into a quiet, efficient tick-over.
How we confirm the size
We don't guess. We look at the room, ask about how you use it, and recommend a size based on the space and the heat load. If you're not sure, we'll confirm the right size before any work starts — and the calculator on our quote page gives you a starting point in seconds.
Common questions
Can I use one unit for two rooms?
A single wall-mounted unit cools and heats the room it's in. If you want several rooms cooled, you'd usually need a unit in each, Ask John about options for cooling more than one room.
What if I pick the wrong size?
We confirm the right size before we fit anything, so you won't end up with the wrong unit. If you're unsure, tell us the room and we'll recommend the right one.
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