How do I choose the right size system?

The size of your air conditioner will depend on a number of factors:

How many rooms you would like to cool – choosing a unit to cool a single room is relatively simple, however if you would like to cool multiple rooms this requires more in depth consideration. Window/wall box units are a good choice for single room cooling. Multi-split systems are usually used for three or more adjacent rooms (these may be high-wall, floor-mounted or ceiling cassette systems) and ducted systems are usually used for whole-of-house cooling. It is recommended that professional advice be sought to determine the type of system most suited to your individual needs to maximise the system’s energy efficiency and lifespan.

Room size – It’s important to choose an air conditioner with the correct cooling output or capacity (usually measured in kilowatts) for the space, this will ensure that the system works most efficiently. Selecting an air conditioning unit that is the wrong capacity for the size of room not only results in poor performance, but also in increased energy use and operating costs. It can also reduce the life-span of the system.

Room design/orientation – The amount of shading and insulation a room has as well as the ceiling height and roof type will all play a role in determining the correct capacity air conditioner.

As all homes differ in character, you should get a qualified contractor to visit your home and provide a detailed heat load calculation/ assessment (the sum of all the heat sources of a space). However it is possible to get a rough estimate of the cooling output you will need by using an online tool, for example the size calculator provided on the Australian Institute of Refrigeration, Air conditioning and Heating (AIRAH) FairAir site (

You might also find our quick reference guides helpful:

Download our quick guide to choosing an air conditioner

Download our checklist of things to consider

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