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What Size Split System Do I Need?

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What Size Split System Do I Need?

Summer is just around the corner, and in this part of the world, that means one thing—heatwaves and stifling temperatures. Thankfully, we have air conditioning to keep us cool, and if you’re in the market for a new air conditioner, you may be wondering what size split system you need. 

Asking yourself, ‘what size aircon do I need?’ before rushing out and buying one is important. If a system is too big for the space, it will waste power, and if it is too small, it will struggle to cool your space. This can result in early wear-and-tear, and end up costing you more in the long run. 

Why choose a split system?

If you’ve decided on a split system already, chances are you’ve done your research. If you are still tossing up, however, here are a few reasons why a split system may be better for your space, rather than a ducted system

  • The biggest reason is size. If you have just one or two rooms to be heated or cooled, a split system is more cost-efficient—cheaper to buy, and also run.
  • It is easier and cheaper to install, and can usually be done in just one day. 
  • While they are wall-mounted, there are a range of styles and designs to choose from, to fit into your home aesthetic seamlessly.
  • They are easily controlled, and this can be done by remote, or by smart technology through phones.

What size air conditioner do I need?

Once you’ve decided on a split system, the next step is to work out what size split system you need. When talking about size, it refers to the power of the system, not the width or length of the physical system itself. Calculating the size of the split system air conditioner you need can be done with a simple equation, and the measurements of your space to be cooled or heated.1 The following are approximates, and your space may differ slightly in ceiling or other measurements. If in doubt, contacting a professional may save you money long term!

First, calculate the floor area of the room you are going to be heating. Measure the length and width of this space, and multiply them to get the metres squared (m2). If your room is five metres by six metres, your answer would be 30m2

Next, you need to work out your ceiling height. Ceilings are usually 2.4m high as standard, but some can be 2.7m, or even 3m. 2The watts (unit of power) will differ according to these heights. Depending on your ceiling height, you will need to calculate your floor space by the watts below:

  • 2.4m = 150 (watts)
  • 2.7m = 160 (watts)
  • 3m = 175 (watts)

If your ceiling height was 2.4m, and your floor space was 30m2, your calculation will be as follows:

  • 30m2 x 150 watts = 4,500 watts.
  • 4,500 watts = 4.5 kilowatts. Kilowatts (kW) is a standard unit of how power is measured. 

You would need a split system that had a 4.5kW capacity. With this measurement, you are able to figure out what size split system will work best for you. Anything under 4.5kW would probably have to work harder to cool your space, costing you more in electricity, as well as general maintenance. Anything too far over may cool your space down too quickly, losing dehumidifying ability, and causing more wear-and-tear than would otherwise exist. There are also other things that may affect the size of the system that will work best for you. 

Other factors to consider

While the size of the unit is the most important aspect of choosing a split system, there are other things to also consider. How many rooms are you wanting the split system to cool or heat? Does your house have insulation? Where will your system be installed? Can doors to that space be closed, or is it an open-style room? 

Spaces to be cooled

If you are happy to have one central room cooled or heated in your house, you can use our calculation to determine the size of your split system. If, however, you are wanting the air conditioner to reach a little further (perhaps in the kitchen just off your main space), you will need to add that floor space into your measurements, which will increase the capacity of the  system.

Unfortunately, split systems don’t handle walls particularly well, so if you have two distinct rooms that you need to cool, you may be better getting a unit for each room (multi-split system).


Depending on how old your property is, your roof may not be insulated. Insulation helps to regulate the temperature of your home, keeping cool air trapped in summer, and warm air trapped in winter.3 When a property has insulation and air conditioning, the insulation helps to maintain the cool temperature, reducing the workload of the air conditioning system. The air con system may struggle to maintain the temperature in a house without insulation, particularly in hot weather. This will increase your power bills, and wear down the system more quickly. It may also require a bigger system to be purchased in the first place. 

Knowing whether your space is insulated or not is important when choosing a split system size.

Location of system

It’s important to install your split system in a high position, which allows cool air to flow downwards, and makes the system work less hard. If you have to place your split system slightly lower, you may need to get a larger unit to ensure the room is still being cooled at the most efficient capacity.

The outdoor unit also needs to be considered when looking at location. As split systems have indoor and outdoor units, ensuring you can have the outdoor unit installed on a north or south facing wall is best. As the sun hits east and west facing walls during the day, installing a system in these locations means the outdoor unit will heat up. This increases workload on your entire system, and may mean you need a system with larger capacity. 

Closed or open?

If you have a living or office space that is a single room, and can be closed off by a door, our calculation will work for you. If, however, you have a lot of windows, particularly uncovered, or the space to be cooled is a little more open, you may need a slightly more powerful unit. The flow of air conditioning means that it will flow down and cool spaces that are warmer. This is easier in an enclosed space, and a little harder when going around a corner and down a hallway. If your entire space is open, or you have multiple doors that are used a lot throughout the day, opting for a more powerful system will ensure you get the most efficient air conditioning. 

Electricity costs

Making sure your air con system is the best fit for you and your space will be the most efficient way to run a unit. If you buy a unit that is too big, the running and maintenance costs will increase dramatically, because it is using more power (without needing to), and has more workload. Systems that are too small face similar issues – your unit will overwork itself to cool the space, also using more power, and wear out more quickly. Air conditioning innovation has come a long way, and there are a lot of brands to choose from, so you can be sure to eventually find the perfect fit for you. Spending a little more on your air con to get a high-standard unit is one of the best ways to ensure a balance of efficiency and capability. It will also save you money in the long run, in power bills and maintenance or repair costs. 

If you are overwhelmed by the choices, or just want to make sure you choose the best option for you, getting in touch with a professional can help. Air conditioning specialists know these equations back and forth, and are aware of all the ins and outs of other factors that may affect your decision. They also know just as much, if not more, about different brands and systems than salespeople in electrical stores. If you would prefer to do it on your own, however, make sure to double-check your measurements, and factor in other aspects, like insulation. This way, you will know exactly what size split system you need.


  1. 2016, What Size Air Conditioner Do You Need For Your Home?, Actron Air. 
  2. Brian Ashworth, 2020, Room Height, A New House. 
  3. 2017, Benefits of Insulation on Air Conditioning, Clements Care.