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Choosing the Right Sized Air Conditioner

Choosing the right air conditioner is trickier than you might think. A unit that is too small won’t cool your home sufficiently, but getting a larger model isn’t always the answer. An air conditioner that it too big for the space is expensive to operate and can be just as inefficient as a smaller model if it turns itself off once the ambient temperature has been reached. So it’s important to do a little bit of planning and research before you make a purchase.

The first thing to consider is the area you would like to be cooled. Size is an important factor and will be discussed later, but there are other considerations to factor in. Is the room insulated? A non-insulated area might require a larger model than an insulated one. How much direct sunlight does the room receive and when does it receive the bulk of sunlight? The afternoon sun is hotter than the morning sun so a west facing room will need something more powerful.

The capacity of an air conditioner is measured in British Thermal Units (BTU) and power output in kilowatts (kW). To determine your needs, start by measuring the room you would like to cool. If the space isn’t a neat square of rectangle, divide the space into squares and triangles and measure those. As a rough guide, you will require around 80 watts per square metre for bedrooms and 125 watts per square metre for living spaces.

Finally, you should check out the unit’s energy efficiency rating. For air conditioners, this is measured using a ten star scale. More energy efficient models will have more stars. A more energy efficient model uses less electricity, is cheaper to run and better for the environment.

The most common types of household air conditioners are:

Split systems

These are comprised of a cooling unit on the inside of the house and a unit on the outside that blows out the heat. They are usually the lowest cost option.

Reverse cycle

Reverse cycle air conditioners are able to both cool and heat the home and as such, offer greater flexibility.

Inverter system

Air conditioners that use inverters are able to regulate their temperature rather than turning themselves on and off. Inverter systems are usually the most expensive of the wall unit options.


Ducted air conditioning uses a large fan, which is placed outside the home, to pump air through ducts in the ceiling (or, in rare cases, under the house). It is used to cool multiple rooms at once.

If you are planning on purchasing a reverse cycle air conditioner to heat your house, you will also need to work out your heating requirements. The same factors – insulation, sunlight – apply here. Your heating needs will depend on your particular climate, but a Brisbane home should need about 60 watts per square metre.

If you need any more help choosing an air conditioner, contact us to talk to one of our experienced Crown Power technicians.