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What size air conditioners do you need for your home?

30 Sep 2021

Home Designs

modern living room

When looking for house and land packages in Perth and their accompanying air conditioning units, some research and a general understanding of the basic principles are advisable. 

There’s no need to worry – when you choose to build your new home with Residential Building WA and choosing one of our incredible single storey home designs in Perth you will have access to our team of experts who can help guide you in choosing the right units for your space. 

For your own interest and reference, here is our rough guide to the principles and aspects to consider when making the right decisions about air conditioning. 


Australian air conditioner sizes are represented by their kilowatt (kW) capacity output figures. This number is not to be confused with the power input, which refers to the power needed to produce the listed cooling and heating output of each unit.

When it comes to air conditioning units and cooling your home in the brutal Australian summertime, efficiency is the key to everything. The most energy-efficient unit is actually the one that will cool your space slowly, steadily using its intended cyclical method. If your air conditioner is too big and powerful it will certainly cool your house down quickly but will then switch itself off before it finishes the full cycle that it is designed to perform. Your space will start to warm up again and so the unit comes back on. Repeat that process over and over and pretty soon your power consumption is much higher than it would have been with the correct-sized units for your home.

Conversely, if your air conditioner is too small it will be running in a constant state of ‘overdrive’ as it tries to cope with the size of the space. Unless it is way too small it should still be able to keep your house cool, but it won’t be functioning the way it is supposed to. High-level operation at all times will mean that efficiency is seriously compromised and it will use significantly more electricity.

Factors that will affect the size of the air conditioners you require

Successful air conditioning can be a bit more complex than it appears at first and involves more than just measuring the space and picking the appropriate unit. There are several other factors that can have a surprising amount of influence on the size of the air conditioner that you will require to control the temperature of your home with maximum efficiency. When you choose your single storey home designs in Perth from Residential Building WA you need not overly concern yourself with some of these factors, as our standards are of the highest level and negate the issues. Out of interest, however, here are a few that we feel are worthy of mention. 

House/room size

The size of the house and individual rooms is certainly a key factor in determining your air conditioning needs. The basic rule of thumb is that you will require a minimum of 1 – 1.5kW of cooling potential per 10 square metres of space. Smaller rooms of 20sq m or less will generally only need 2 to 2.5kW and areas of 40sq m or larger will require capacities of 4kW and above.

The trouble is that this ‘rule of thumb’ can go wildly askew depending on some of the other contributing factors. For example:

stylish modern white blue


The amount and type of insulation in your house will dramatically affect its ability to maintain a constant temperature, whether it be hot or cold. A well-insulated property like the ones you can expect to find when you browse Residential Building WA’s house and land packages in Perth won’t need the same level of heating or cooling capacity when compared to one with substandard insulation. The number and size of windows and skylights that your property has, and their efficiency level are also important elements in the overall temperature stability of any space.


The demands on any air conditioning system are bound to be greater in the hotter regions of Australia and Perth certainly isn’t without its share of glorious sunshine! If your house has large windows that get a lot of sun on them then you can expect the inside temperature to be exponentially higher. This is also something to consider very carefully when looking at our single storey home designs in Perth and deciding how you would prefer to orient your new home if that is an option.  

Lighting and electrical devices

Other, perhaps unexpected, influences on the size of the air conditioners you will need, include what type of lighting you will use and how much of it there will be. Inefficient lights give off a remarkable amount of heat and can increase the ambient temperature significantly. Have you ever thought about how much heat energy comes off your electronic devices like laptops and mobile tablets? Individually they don’t seem big enough to make a difference but when you multiply them by the number of people inside a home you start to realise that they constitute another marked contribution. Oh, and don’t forget that people give off tremendous amounts of heat too!

woman looking tablet

Calculating the size of air conditioners for your property

There are any number of online air conditioning calculators available and they can be a very useful guide indeed, but there is no substitute for real experience. At Residential Building WA we have a team of dedicated professionals who have spent decades working in this field and know exactly how to select the right units for your space. When you choose your new dream home from our catalogue of single storey home designs in Perth or perhaps choose one of our home and land packages in Perth you are guaranteed access to their boundless expertise and guidance. They can calculate the exact air conditioning requirements of your space for you and take the guesswork out of it, leaving you to ponder other important issues – like what shape the pool will be…