What Size Ducted Aircon Do I Need

16-01-22 | Air Conditioning

What Size Ducted Aircon Do I Need? Ducted Air conditioners are great at keeping us comfortable year round in Queensland. But before you buy a new ducted air conditioning system, make sure you know what size unit is needed. The size of your air conditioner will depend on a variety of factors such as the size of your home, the amount of space that needs to be cooled & how well your home is insulated. You should make sure to measure your house carefully before you buy an ducted air conditioner!

Find out about the size of your home

A good general guide to determining what size ducted aircon you need is using the watts per square meter method; this is what the majority of size calculators are based on. To do this first, determine the floor area of your home. To calculate the area of your home you simply multiply with room length by room width. For example:

Bedroom 1
Room length X room width = X square meters
3m X 3m = 9 square meters

Do this calculation for every room in your home including common areas such as hallways etc. You can leave out any rooms that don’t require air conditioning such as bathrooms , laundries & cupboards.

Once you have the area of each room, add them all together. For Example:

Bedroom 1 = 9 square meters
Bedroom 2 = 8 square meters
Bedroom 3 = 8 square meters
Bedroom 4 = 8 square meters
Kitchen/Dining = 30 square meters
Living = 28 square meters

Total Area = 91 square meters

Now we have the total square meters we can move onto the next step to determine the correct size! Make sure to measure your house carefully before you purchase an air conditioner!

Determine the required cooling capacity for your ducted air conditioner

Now that we know how many square meters we need to cool we simply multiply by 0.16kW, this number is a general rule of thumb recommended for Brisbane & Gold Coast homes. For Example:

91 square meters X 0.16kW = 14.56kW Total Cooling Capacity

So to cool this entire space we require an air conditioner with at least 14.56kW cooling capacity! 

Now you have to think about how much of this space you would like to cool at the same time (coverage) to get to your final required cooling capacity. 

It’s rare to Size of ducted aircon to cool 100% of the home at any one time as this will result in a larger unit which will have higher airflow rates that will be difficult to manage when you are trying to cool only a few rooms in the home. 

The sweet spot for coverage is around 70%, in other words we want to size the air conditioner so it has the power to cool at least 70% of the home at once. To calculate this simply take your total required cooling capacity and multiply by 0.7. For Example:

14.56kW Total Cooling Capacity X 0.7 = 10.19kW

So there we have it, we need a ducted air conditioner unit that has a rated cooling capacity of at least 10.19kW to cool up to 70% of the home at one time.

Air conditioners have at least three capacity in their specifications:

  • Min cooling capacity – This is the minimum cooling capacity the unit can achieve, the lower this number the more efficient your unit will be when cooling your bedrooms at night when there is little heat load reducing your electric bill.
  • Rated cooling capacity – This is the unit’s tested capacity and is usually most efficient when running at this capacity. We use this value when determining unit size.
  • Max cooling capacity – As the name suggests this is the maximum capacity, the higher the value the better chance your air conditioner has at coping with extreme heat waves.

Assess how well your home is insulated!

The method of sizing an air conditioner shown above is a general guide rather than an exact science, an air conditioning professional will take into account many factors such as:

  • Ceiling Height
  • Windows
  • Blinds & Curtains
  • House Design
  • Insulation
  • Roof Ventilation
  • Tightness of the home
  • Local Climate
  • Orientation
  • Your lifestyle
  • Desired Temperature

If using our method above to size your ducted aircon it’s best to make sure your home is well insulated & ventilated, speak to your home comfort specialists to get a quote on adding ceiling insulation and solar powered roof ventilators to reduce the load on your soon to be installed air conditioner!

What size ducted aircon do you need?

Selecting what size ducted aircon you need is important because it will affect both  the energy efficiency & performance of your system. What if your ducted air conditioning system is undersized or oversized?

  • Undersized air conditioners will not have adequate capacity to cool your home resulting in the unit running at its maximum capacity at all times increasing your energy bill.
  • Oversized air conditioners may short cycle, this results in the air con unit running for a brief period of time before reaching the desired temperature and shutting off. Oversized ducted systems will struggle to maintain the correct temperature and will not run for long enough to remove humidity from your home.

A correctly sized ducted inverter air conditioner will regulate it’s capacity between the min & max capacity to provide a consistent temperature through the home whilst doing a good job at maintaining indoor humidity between 30-50%.


Using the methods described above to size your air conditioner is a good way to get an idea of what size system you should consider for your home. Before making a purchase we recommend talking to your ducted air conditioning installation specialist, they have specialist software tools such as Plandroid for ducted air conditioning system design to properly confirm which size system is correct for your home. Contact our friendly team today on (07) 3067 2396 to help you choose the best solution for your home

Ducted Aircon Sizing


Pin It on Pinterest