Choosing a split system air conditioner


Wall Split Systems:

These have two parts: an outdoor compressor unit and an indoor unit connected by copper pipes. They’re usually used to cool one room, or an open-plan area of up to 60 square metres. The indoor unit needs to be mounted on an external wall, to allow for the condensate water to drain while in the cooling mode.


A type of wall split-system, with one outdoor unit connected to two, three or four indoor units. This can be a good way to cool or heat two or three rooms that are reasonably close together, when separate split-systems or a ducted system aren’t possible due to space limitations or roof space restrictions.


The best option for temperature control throughout a large home or office. This consists of a central unit connected by ducts to air outlets and sensors in each room, with a control panel to set the target temperatures and the zones of the area to cool or heat.


These models can vary the compressor speed. That means the compressor (in the outdoor unit) doesn’t need to switch on and off continuously, but instead just speeds up or down as need demands. By not actually having to stop and start several times a day, there’s less stress on the compressor and less electricity is used, so inverter models are generally more efficient and cost less to run. They can maintain a set temperature within a narrow range. Most split systems on the market these days are inverter models.

What size air-conditioner is right for my needs?

We choose a model with equal or slightly greater capacity for the room or building you wish to condition. For example, if you calculate the room needs a 6kW model, then we look for an air conditioner with rated cooling capacity in the range 6kW to 6.5kW. It’s probably a safer bet to get a model slightly above the required capacity than slightly below it; a little extra capacity may help in extreme temperatures.
o Models too powerful for the room size may run frequent short cycles to achieve the target temperature. This can result in the room getting too cold or hot, increased power usage and running costs; and wear and tear on the system.

Underpowered models may have to run more often at maximum output, struggle to make temperature on high ambient days, dry the air too much and cost a lot of money to run. Also, they will suffer from excessive wear.

How to use your air-conditioner

Heating and cooling appliances account for about 40% of the energy usage of the average Australian home and up to 70% to commercial buildings. . To save money when running your air conditioner, there are several things you can do.

  • Size: Having the correct size of air conditioner is an important first step
  • Star ratings: a model with more stars will be more efficient and use less power than a model with fewer stars
  • Make your home as energy-efficient as possible
  • Use Economy mode (“Eco mode”) if your air conditioner has one
  • Set the thermostat (target temperature) to 23°C so the system doesn’t have to work too hard and use more power than really necessary.

Keeping a reasonable temperature

On a hot day – say 33°C – you might be tempted to put the air conditioner way down to 20°C to get the room cool as quickly as possible. But if you can cope with setting the temperature at 25°C, you will not only save on wear and tear on the air conditioner’s motor, you will save big on your energy bill. Each degree cooler, or warmer in winter, can add about 10% to the running cost.

The same principle applies in winter. If it’s 10°C outside, try setting the indoor temperature to 21°C rather than 25°C.
It also depends on the external temperature. Generally you’ll get better efficiency by aiming for a maximum temperature differential of about 8°C. So on a 35°C day, set your indoor thermostat to 27°C. Realistically, most people will still go for a cooler temperature, but try not to go too far beyond that 8°C difference. You can probably aim for a bigger differential if your house is very thermally efficient (well insulated, double glazed etc).
Dehumidifying and “dry” mode.

Your air conditioner is a good option for controlling warm humid air. Cooling mode not only cools the air but also removes some air moisture, which makes the air feel more comfortable.

Many models also have a “dry” or “dehumidify” mode to dry the air, which is best used when the air is warm and very humid. The indoor fan speed is reduced so that the air spends longer moving over the cooling coils, in order to extract more moisture from the air. Dry mode can be an efficient and effective option in those conditions as reducing the humidity makes the air feel cooler and more comfortable. But when it’s very hot and only moderately humid, cooling mode will be much more effective.