What Size Split System Do I Need? A Room-by-Room Guide

Sizing is the most important decision when buying a split system, and it's the one most often got wrong. The rating in kilowatts refers to how much heating or cooling the unit produces – not how much power it uses. Here's how to land on the right number.

Start with floor area

As a starting point for an average, reasonably insulated Bendigo home with 2.4 metre ceilings:

Up to 20 square metres (a bedroom): 2.5 kW.
20 to 30 square metres (large bedroom or small living area): 3.5 kW.
30 to 45 square metres (living area): 5.0 kW.
45 to 60 square metres (large open living): 6.0 to 7.1 kW.
60 to 80 square metres (open plan living, kitchen and dining): 8.0 to 9.0 kW.

Then adjust for the room itself

Those numbers move depending on the space. Add capacity for high or raked ceilings, large west-facing windows, poor or no ceiling insulation, an uninsulated Colorbond roof, or an open stairwell. You can often take capacity off for a well-insulated room, a south-facing aspect, or a space shaded by verandahs and trees.

Windows and orientation matter more than people expect

A big west-facing window can add as much heat load in a Bendigo summer afternoon as several square metres of floor area. Double glazing, external blinds or awnings all reduce what the unit has to fight against – and sometimes let you drop down a size.

Why undersizing is a problem

An undersized unit runs flat out all day and still doesn't reach temperature on the extremes, which is exactly when you need it. It uses more power doing it, and running constantly at maximum shortens its life.

Why oversizing is also a problem

People assume bigger is safer. It isn't. An oversized system cools the air quickly then shuts off, which means it never runs long enough to pull moisture out of the air – you end up with a cold, clammy room. That stop-start cycling also wears the compressor and wastes power on every start-up. In heating, it makes the temperature swing up and down instead of holding steady.

Get it measured

A quick walk-through with a tape measure and a look at the ceiling insulation, window sizes and orientation takes ten minutes and removes the guesswork. We'd rather size it right the first time than come back and swap a unit that was never going to keep up.

Need a hand?

We're a local Bendigo team and we're happy to take a look. Give us a call on (03) 5444 4677 for honest advice and a free quote.