How to size an air conditioner for Australian rooms
Choosing the correct kilowatt cooling capacity for an air conditioner is critical. An undersized unit will run continuously at full load without ever cooling the room, driving power bills through the roof, while an oversized unit cools too quickly without dehumidifying, leaving the air cold and clammy.
In temperate to warm Australian climates, a general rule of thumb is 140 to 150 watts of cooling power per square metre of floor space for standard 2.4m ceilings. For large bedrooms and studies (up to 20 m²), a 2.5 kW unit is common; for medium living areas (up to 35 m²), a 3.5 kW to 5.0 kW unit is typical.
Factor in heat load drivers such as large north-facing or west-facing windows, uninsulated metal roofs, and high 2.7m or 3m ceilings. Adding thermal blockout curtains and roof insulation significantly reduces the required unit capacity.
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