No matter how hot under the collar you get, buying an air conditioner should never be an impulse purchase. It's an expensive, long-term commitment that has big implications for your power bill and comfort levels alike – so it's important to do your homework before installing one. While it's tempting to just opt for the biggest air conditioner you can get, bigger isn't always better. So how can you find out the capacity you need?

These four things have the biggest impact on what size air conditioning unit you'll need:

1. Room size: What's the length, width and ceiling height? While floor space is important, so is total volume – a room with high ceilings will require more energy to cool.
2. Insulation: Are the ceilings and walls insulated? What's underneath and on top of the room? Ceiling insulation is one of the biggest factors in making your home thermally efficient.
3. Location: Where do you live? A room in Darwin will need a more powerful air conditioner for cooling, compared to an otherwise identical room in Hobart. 
4. Orientation: Which way does the room face? A large north- or west-facing window can let in a lot of heat in summer, whereas a shaded, southern-facing window will be cooler. 

PRO tip: Ceiling insulation has the biggest impact on how big an air conditioning unit you'll need. If you don't have roof insulation, consider installing it – it'll save you money in the long run, as you can get away with a smaller, cheaper air conditioner, as well as ongoing running costs.

SPLIT vs. MULTI SPLIT AIR CONDITIONING SYSTEMS

Split system air conditioning

However, there are advantages to doing it this way. Firstly, it’s often cheaper than installing a central system, and, as each system is self-contained, if one unit breaks down, the others remain fully functional. Even though they’re the cheapest type of air conditioning, single splits are effective and energy-efficient systems. Their versatility makes them great for all kinds of applications and they’re extremely popular with small businesses.

Multi-Split system air conditioning

Multi-splits work in exactly the same way as single splits but, depending on the model, you can connect up to nine indoor units to one outdoor unit. They’re most frequently used in places like restaurants, offices, doctor’s surgeries and shops.

It’s always preferable to have fewer outdoor units, particularly if you lack space or want to preserve your building’s external appearance. That gives multi-splits a distinctive advantage over several single splits.

Another selling point is that you aren’t limited to using just one type of indoor unit. If you wanted to, you could have any combination of wall- and ceiling-mounted air conditioning units, along with an air curtain over the entrance. However, multi-split systems are slightly more complex and require more pipework than several single splits. That can make the installation more expensive and take longer, particularly if you’re only looking to install a few indoor units.

Ultimately, the best solution depends on the layout of your building and the heating and cooling capacity you require.