How to size a split system for your bedroom (and not get oversold)

Every second aircon quote we see for a Pakenham bedroom pitches a 5 kW unit. Almost none of them actually need it. Here's how to size it right.

The rough rule of thumb

For a well-insulated Pakenham home (built after ~2005), a split system in kW = your room's floor area in m² divided by 10-12. So a standard 12 m² bedroom needs about 1.0-1.2 kW of cooling, but the smallest split you can buy is 2.5 kW. So a 2.5 kW is more than enough for anything from a 12 to 20 m² room.

Quick sizing table for SE Melbourne homes

• Small bedroom (10-15 m²): 2.5 kW split
• Large bedroom or small living (16-25 m²): 3.5 kW split
• Standard living / open plan (26-40 m²): 5.0 kW split
• Large open-plan (41-55 m²): 7.1 kW split
• Big open living + kitchen (56-75 m²): 9.0 kW split or step up to multi-head

Why oversizing costs you money

Bigger isn't better. An oversized split short-cycles, it hits the setpoint fast, kicks off, then kicks on again 3 minutes later. That's rough on the compressor, chews power, and leaves the room feeling humid because it never runs long enough to dehumidify properly.

The right-sized unit runs steadier, dehumidifies properly, uses less power, and lasts longer. So don't let anyone talk you into a 5 kW for a bedroom.

Brand notes

For bedrooms, Mitsubishi Electric's MSZ-AP series runs 19 dB indoor, that's about as quiet as a library. Perfect for kids' rooms and light sleepers. Costs a bit more than Kaden but you notice at 3 am.

For living areas, Kaden gives you the best bang for buck, the KS series has a 5-year warranty and R32 inverter tech at Mitsubishi-lite pricing.

Get us to quote you a size we'd actually install ourselves. We'll pick the smaller of two options if it does the job, reputation is worth more than an extra kW in someone's kid's bedroom.