What actually drives the size
Floor area is the starting point and the least interesting part. Two rooms of identical size can need noticeably different capacity depending on everything else.
- Ceiling height — volume matters more than floor area.
- Glazing: how much, which direction it faces, and whether it is shaded.
- Insulation in the ceiling and walls, and whether the room is under a hot roof space.
- Which way the room faces, and what the western sun does to it after 3pm.
- Whether the space is closed off or open to the rest of the house.
A west-facing living room with a wall of unshaded glass under an uninsulated roof is a completely different problem from a shaded south-facing bedroom of the same size.
Why oversizing is a real problem
An oversized system pulls the temperature down quickly and then shuts off. Because it has not run long enough to remove much moisture, the room ends up cool and humid rather than comfortable — which in Brisbane is precisely the wrong result.
Short cycling is also harder on the equipment than running steadily, and it makes the system noticeably noisier because you hear every start and stop.
Comfort is temperature and humidity together. A system that only addresses the first has done half the job.
And undersizing
An undersized system runs continuously on the hottest days and still does not reach the temperature you set. It costs more to run than a correctly sized one doing the same job, and it wears out sooner because it never gets a rest.
How we work it out
We look at the room rather than the floor plan: the glazing, the aspect, the ceiling, what is above it, and how the space connects to the rest of the house. Then we recommend a capacity within the range we work in — roughly 1.5kW to 18kW, covering everything from a small bedroom to a large open living area.
We install reverse-cycle split systems, which means the same unit heats in winter. We do not do ducted.
On brands, we have preferences based on what holds up: Mitsubishi Electric, Daikin, Mitsubishi Heavy Industries and Haier, with Fujitsu also fine. Those are the brands we regularly install, not a dealership arrangement.
Sized properly
Get the right system for the room.
Reverse-cycle split system installation across Greater Brisbane, quoted fixed before the work starts.
