Split System Air Conditioning – What it is, and how it works

In the Australian climate, air conditioning is not so much a luxury as a basic necessity — heatwaves are officially our most deadly type of natural disaster. Split system air conditioning is very common in Australian homes, and you’ll probably see the term start popping up the moment you start googling anything about air con.

But what is a Split System air conditioner? Why is it called that? Is it different from a reverse cycle air conditioner, or an evaporative? How is it different from ducted air con, and what is a “multi head split system”. Let’s take a moment to run through the essentials and help you understand what a split system is, and what it does.

Key Takeaways

• Split system air conditioners are the wall mounted air conditioning units found in many Australian homes. They’re different from ducted air conditioners, which are mounted inside the roof and blow air through vents in the ceiling.
• They’re called split systems because the mechanism is split into two parts — a cooling unit inside the house, connected to an outside unit by copper pipes running through the walls.
• They work by blowing air over coils of cold liquid to cool it down. The liquid then takes the heat from the air to the outside unit, where it’s blown out as hot air.
• They’re good at cooling one or two rooms, but less efficient for multiple rooms and large spaces.
• They cost a few thousand dollars to install, and last around a decade if they’re well maintained.

What is a split system air conditioner?

A split system is a common type of air conditioner in Australia. They’re generally easy to spot in a house, as there’ll be a large white box (generally about a metre wide) attached to a wall above head-height. There’ll also normally be a small remote control somewhere nearby to operate it, often mounted on a wall.

This is different from ducted air conditioning — the most common alternative to a split system — where the only visible signs are normally vents in the ceiling, and the controls on the wall.

The term is actually a bit misleading, as in reality a lot of ducted air conditioners are a type of split system. Technically, what we normally call a “Split System” is officially called a High Wall aircon unit — (for hopefully obvious reasons). But normally if you’re talking to air con companies or looking up brands on the internet, the two options you’ll normally be discussing are ducted AC or a split system.

How does a split system air conditioner work?

Most cooling technology nowadays — including refrigerators — work on a very similar principle, and have four basic components:

• • An Evaporator
  • A Compressor
  • A Condenser
  • An Expansion Valve

To make it all work, a chemical known as refrigerant travels through these four components and moves heat around.

First, the expansion valve releases very cold liquid refrigerant into the evaporator. This is a series of coiled metal tubes that the cold refrigerant travels through while a fan blows air over the coils. This is where the cool air comes from in an air conditioner — it’s normal air blown over coils of chilled refrigerant to cool it down.

At the same time as it cools down the air, it’s warming up the refrigerant liquid, and causing it to evaporate into vapour or gas — which is why the coils are called the evaporator. This gas then goes into the compressor where it gets changed from cool gas at normal pressure to highly pressurised hot gas.

That might sound like black magic, but it’s actually just clever physics in action. But that might be a question for another blog. Although if you’re curious, there’s a good explanation on the live science website.

Once it’s passed through the compressor, the hot, high-pressure refrigerant gas then goes into the condenser – which is another set of coils like the evaporator. But in this case, the air is blowing across hot refrigerant, which means hot air is blown out (you’ll know that if you’ve ever stood near the outside part of an aircon unit), and the gas is cooled down and turned back into liquid — still under high pressure.

At this point it moves into the expansion valve, where it gets turned back into a cold, low pressure liquid (by clever physics again), and starts the cycle all over again.

This is the basic idea of air conditioning.

• • The air blown through the evaporator cools things down
  • The heat is absorbed by the cold refrigerant liquid, and moved to the condenser
  • The condenser blows air through the refrigerant gas to cool it down (blowing the heat elsewhere)
  • The refrigerant liquid moves back through the expansion valve to continue the process

Why is it called a “Split System Air Conditioner”?

It’s called a “split system” because the system is divided into two separate units — one of which normally goes on the outside of the building. This is connected by insulated copper piping to the inside unit, which is normally mounted high up on a wall in the room you want cooled.

The indoor unit normally just contains the evaporator, which is where the cooling happens. The outside unit normally has the compressor, the condenser, and the expansion valve. This means the inside cooling unit is a lot quieter (compressors are pretty loud machines), and the hot air from the evaporator is blown outside. The inside unit just needs the evaporator, a low-noise fan, and the electronics to operate the system and talk to the remote control.

How is a split system air conditioning different from ducted AC?

Now, there are two answers here — the normal answer, and the technically correct answer.

The answer people are normally looking for when they ask this question is that split system air conditioning is normally just used for one room or living area. It has a wall-mounted cooling unit which is designed specifically to cool that room.

Ducted air conditioning is normally mounted in the roof, and designed to cool a large part of the house. The name comes from the many air-ducts in the roof that lead from the cooling unit to the various rooms. Ducted doesn’t have the wall mounted air con units you see with a split system — normally the only internal sign that a house has ducted is air vents in the roof of many rooms, and a wall mounted control pad in at least one room.

There are also different types of ducted air con — evaporative and reverse cycle being the two most common options.

That’s the answer people are normally looking for when asking that question. But it’s worth knowing that comparing “ducted” and “split system” air conditioning is a bit tricky, as many ducted aircon units are actually split systems.

Technically speaking, “split system” just refers to the mechanism being in two parts — one inside and one outside. There’s actually a range of different types of split system. This can include:

• • High Wall units
  • Ducted systems
  • Ground or floor mounted units
  • Cassettes (the box-shaped aircon units you sometimes see hanging down from the roof in big function centres)

What we normally talk about as a “split system” is officially a high wall split system, because — in case it’s not obvious — it’s mounted high on a wall.

But normally, if you’re talking to people about “split system” vs “ducted” air con, then a “split system” is the type of air con that has a big plastic box on the wall and a remote control, and “ducted” is the one with roof vents in different rooms and a touch screen on the wall. And a ducted system will normally be either reverse cycle or evaporative — which work quite differently, but don’t look much different from inside the house.

What’s a “multi head” split system?

A multi head split system is simply a kind of split system where there is more than one indoor unit connected to the same outdoor unit. The outdoor unit will have the same setup — with a compressor, a condenser, and an expansion valve. But the pipes that lead inside the house will be connected to several cooling units, each in a different room with their own evaporator.

They’re normally an option for when someone needs more than one area cooled, but doesn’t want to go all out and install a ducted system. They can also be a workable option in situations where a ducted system is not practical due to the construction of the building.

Are all split systems reverse cycle?

No. Although that might not mean what you think. If what you’re actually asking is “can you get an evaporative split system”, then no — evaporative coolers work differently from the air conditioning cycle described above. Evaporative coolers draw air from outside, cool it, and blow it inside — so the process is very different.

However, there are split systems that only cool — they can’t heat.

A reverse cycle air conditioner uses the same principles described above, but has one extra feature — the process is reversible. This means that reverse cycle AC units can heat as well as cool. When you switch your reverse cycle air conditioner over to heating mode, the compressor and expansion valve reverse the way they work. This means the evaporator and the condenser switch jobs, and your air con is now blowing warm air inside the house, and cold air outside.

Not every split system air conditioner is built like this though — particularly when you’re talking about older air con units. So it’s quite possible to come across split system AC that only works as a cooler.

What sort of houses/spaces is split system aircon best for?

The key thing about a split system unit is that it’s best for cooling a single room or small indoor area. As such, they’re a great choice for either a small unit, or a home or business where you have one area that you particularly need to keep cool — such as a bedroom or home office. Because a single room split system is generally a lot cheaper to run than a full ducted system, this makes it far more economical for cooling one specific room.

They’re also a workable option for a home or building where ducted air conditioning isn’t really a viable option — such as a multi-level apartment that doesn’t have a roof space.

Should I have a split system in every room?

This is generally a bad idea. While a single split unit is normally cheaper to run than a whole ducted system, it’s only cheaper because you’re only cooling one small area. If you’re looking at cooling multiple rooms at once, then a ducted unit is going to be far more efficient than multiple split systems. And given many modern ducted systems will allow you to set which rooms need to be cooled — or even set the temperature room-by-room — there are not a lot of benefits to buying split systems in bulk.

Not to mention the fact that your outside walls would have a bunch of different aircon units cluttering up the place and blowing hot air at you as you walk past.

If for some reason you need multiple spaces cooled and a ducted system is not a viable option, you’re normally a lot better off going for a multi-headed split system. That gives you a lot of the benefits of having multiple split systems, but in only requires one external AC unit, it’s cheaper than several split systems, and it’s more energy efficient.

Are there limits on where I can install a split system?

One of the main limits on getting a split system air conditioner is wall space — you need an area of wall where you can mount the cooling unit. This doesn’t have to be an external wall (as in a wall on the outside of the house), but it has to be a wall that the installer can run copper pipes through to connect to the outside unit — so it can’t be a fibreboard partition, for example.

Also, it’s worth remembering that air conditioners often cause a little bit of moisture — the air from the room blowing across the evaporator coils generally causes condensation (same as an icy cold can of drink gets condensation on it when you take it out of the fridge and leave it on the counter). While it’s not a LOT of moisture, it’s normally good to avoid installing the cooler near anything that doesn’t like getting a bit wet now and then — like electrical equipment, or musical instruments that you care about.

When is a split system not the best choice?

Looking broadly at some of the issues we’ve already touched on, situations where a split system might not be ideal could include:

• • When you’re hoping to air condition a few different rooms
  • When your rooms have limited wall space for a cooling unit
  • When your walls don’t have space inside them for the pipes

In addition to these, it’s also worth considering your external space — whether you have a well ventilated location for the external unit on the outside of your house.

This isn’t often an issue, but if — for example — you lived in a block of units and your rear wall opened onto a small enclosed verandah, you’d need to either put up with the aircon taking up room in your backyard and filling the space with hot air when it’s running, or having a moderate sized aircon unit fitted to the front of your house.

Even if these things are true, a split system aircon may still be the best option available for your situation. So if the home described above is a ground floor unit with another unit above it, ducted may not be an option and your choices are a split system or no aircon at all. But these are all factors to consider.

What sizes of split system can you get?

Generally, the size of a split system is measured with a power rating in kilowatts (kW). In South Australia, the split system air conditioners used in most homes normally range from around 2.5kW up to 9kW. This also gives a general idea of how big a space the air conditioner can cool. A 2.5kW split system is generally enough for a single bedroom, while a 9kW is better for a large open-plan space. Any larger and you’re normally better off looking at a ducted system.

The main problem with going too large is cost — a 9kw system will cool a small bedroom easily, but you’ve paid way more than you needed to cool one small room. It’ll also cool very quickly, meaning it will turn on and off very frequently — which isn’t energy efficient, and can shorten the life of the unit.

If your aircon is too small however, you’ll generally find it won’t do its job — it won’t be able to cool the space you’ve installed it in. So a 2.5kw system is probably not going to cut it for your combined kitchen / lounge room / dining area.

What size split system would I need for my space?

There are a few things that can affect what size aircon you’d need for your home, but the table below gives you a rough sense of what different size split system can do.

Size	Area cooled	Possible room sizes	Type of room
2.5kW	Up to 20m²	4m × 5m or 6m × 3.5m	Bedroom / Study
3.5kW	Up to 25m²	5m × 5m or 6m × 4m	Ensuite bedroom / Small living area
5kW	Up to 40m²	6m × 6m or 8m × 5m	Large lounge room / Combined Kitchen/Dining Area
7kW	Up to 50m²	7m × 7m or 5m × 10m	Open-plan living area
9kW	Up to 70m²	8m × 8m or 7m × 10m	Large open plan space

For a general rule of thumb, work out the area of the room you want air-conditioned in square metres. To do that, just measure the width and the length in metres, and then times those two numbers together. Then divide that number by 7.7 — your split system needs a kW rating larger than the result.

So if you want to cool a room that’s 4.9 metres by 6.3 metres, first multiply those two numbers together…

4.9m × 6.3m = 30.87m²

Then, divide that by 7.7

30.87 ÷ 7.7 = 4.009

That means the kW rating on your split system needs to be higher than 4.009kW. So you’re probably looking at needing a 5kW split system to cool a 4.9m × 6.3m room.

Of course, while these numbers can give you a rough idea of the size you’ll need, there are a lot of other factors that can affect things. The layout of your house can change how much the sun will warm up your rooms. The height of the ceilings can change the amount of air in each room and how heat gets trapped. And the location of your home — up in the hills or down on the plain — can influence how warm your home gets.

As such, it’s always a good idea to talk to an expert before choosing a split system, and getting them to do an inspection if possible.

How much to install a split system air conditioner?

This very much depends on what size and brand of unit you buy, who you get to install it, and what sales or deals are on offer. But broadly speaking, you’re normally talking about a few thousand dollars for a new split system air conditioner.

If you found this article by searching for anything to do with air conditioning, there’s a good chance that google is already trying to sneak ads for split systems into your search results — and the ads on your social media will probably start showing up soon. Those prices change pretty regularly, and they don’t take any account for the layout of your house or your specific needs. So if you’re looking at prices, you really need to sit down and do the homework — hunt around, check out the companies that install in your area, and get quotes. Anything else is just wild guess work.

But when you’re shopping around, here are a few valuable tips…

• • Make sure you’re including the installation cost — Many of the prices you see advertised on the internet will be just for the aircon unit itself, and won’t include installation cost. Installing an aircon is not really a DIY job.
  • Not all air conditioning companies are the same — Check reviews. Ask friends for recommendations. Get someone who’ll do it right.
  • Get an inspection if you can — Although it seems like a hassle, it’s a good idea to get quotes from a company that does obligation free inspections, as the person doing the quote will have better information to go on. If a company is quoting over the phone, they’re normally making a general guess about how complicated the installation will be, and what type of system will suit you best — so it’s a little like buying a suit off the internet.
  • Be wary of going too cheap — We all have a budget to work with, so we know the appeal of things being affordable. But remember that, like so many things in life, going low-cost doesn’t always pay off. Weigh up your options, but don’t jump for the cheapest deal and end up paying for a sloppy installation job and an air conditioner that breaks down in a few years, just after the warranty runs out.

If you’re interested, REQ does obligation free quotes for homes anywhere in South Australia. We’d love to help you kick off the hunt for the perfect aircon — and we’re always happy to answer any other questions you might have.

Is it important what brand I choose, or are they all basically the same?

No, not all air conditioning brands are the same, and yes the brand can be important to consider. In air conditioning, the rule is often “you get what you pay for”.

While for many people, it’s tempting to rate air conditioners based on the high-tech toys and features it may have, this is not the most important thing. Rather, it’s very helpful to look at what after-market service the brand offers on their AC units — what kind of warranty do they provide, and how willing are they to fix the problem if the unit breaks down.

Not only is this important if your AC does develop issues, but the kind of warranty and support the company offers is also a good sign of how reliable it’s going to be. Companies that offer a really solid warranty probably aren’t going to sell products that break down all the time.

How long does it take to install a split system air conditioner?

The time needed to install a split system can vary depending on the house, but as a general rule, it will normally take around four to six hours — generally closer to four if there are no complications.

Can I run a split system all day?

Yes. Most modern air conditioners — particularly those made for Australian conditions — are designed to be run continuously for days on end without any issues.

It will be using electricity while it’s running, so having your aircon going non-stop can be a little expensive. But in intense bouts of hot weather, it may be worth the cost — particularly if you have a solar system and can make the sunlight work for you.

Take note, though — it’s important to set the temperature of your AC wisely.

Many people assume that the temperature setting on your AC (also called the thermostat) is a little like an accelerator on a car — when you press harder, it works harder. So if people come into a hot room, they’ll often turn the thermostat on the AC down to 17 °C — even if they only want the room at something comfortable like 23 °C. They assume that’ll make the air con work harder, and cool the space down quicker.

In reality, it doesn’t work like that. The temperature you set is the goal temperature that your AC unit is aiming for, but it doesn’t change how “hard” the aircon is working, or how fast it cools the room. If your split system is capable of cooling the room down to 23 °C (which depends on things like the size of your unit and how hot the day is), it’ll get you to that temperature and then stop cooling until the room starts to warm up again. If it’s not able to get the temperature down that low (if it’s 40 °C in the rest of the house and you’ve left the door open, for example), then turning the thermostat down to an even lower temperature won’t make any difference.

The only difference turning the temperature down low will make is that if it does get the temperature down to 23 °C, it’ll keep going — at which point you’ll soon be reminded that 17 °C is actually uncomfortably cold for most people. Not to mention that the lower the temperature you set, the more electricity you’ll use.

So as a general rule, it’s smart to leave your thermostat at a comfortable temperature — which is normally around 22-24 °C in summer, and around 19–21 °C in winter.

How much does it cost to run a split system air conditioner per hour?

That’s a more difficult question to answer than you might think, because there are lots of factors that affect your running costs. A small split system might cost you 20-30c an hour to run, but that’s only part of the picture. It doesn’t give you a sense of the overall annual cost, which could be anywhere from thirty to several hundred dollars a year.

Some of the factors that will affect your running costs include:

• • The climate your home is in (i.e. how warm/cold it gets).
  • Where your house is located (shaded valley vs sunny plain).
  • What temperature you set the thermostat to (keeping the thermostat at 17 °C in summer will use a lot more electricity than leaving it at 23 °C).
  • How much of the day you run it for.
  • How energy efficient your air conditioner is.
  • How well maintained your unit is (if your unit is not cleaned and serviced regularly, it will be less efficient).
  • How old the unit is (most units loose efficiency as they grow older).
  • How well insulated your house is (if your house gets hot easily, your air con will be working harder to keep it cool).

These are just some of the factors in play.

And of course those factors only affect the amount of energy used by your split system — they don’t influence factors like the price of electricity, or whether you have a solar system that offsets electricity costs.

Just to give an example, here are some average annual running costs for a single split system reverse cycle air conditioner in a small room in different locations around Australia for both heating and cooling.

 

Climate Zone	City	Average Usage Rate	Annual Cooling Costs	Annual Heating Costs
Hot	Brisbane	31.2c / kWh	$155	$46
Hot	Darwin	28.1c / kWh	$140	$41
Average	Sydney	35.3c / kWh	$61	$193
Average	Adelaide	44.9c / kWh	$78	$246
Average	Perth	30.8c / kWh	$54	$169
Cold	Melbourne	26.3c / kWh	$30	$206
Cold	Hobart	29.5c / kWh	$33	$231
Cold	Canberra	26.4c / kWh	$30	$206

Source: Canstar Blue

And this is just comparing how the general climate of the city impacts things.

If you wanted more specifics, Canstar Blue has some useful numbers on aircon running costs.

How to clean a split system air conditioner?

As your split system is running, dust and particles from the air are drawn in by the fan and caught as they pass through the air filter. Over time, this can mean the air filter becomes clogged, restricting the flow of air and causing the unit to cool less effectively. Fortunately, split systems are designed so the filters can be cleaned by the user from time to time.

The exact method of opening up the unit, removing the filters and cleaning them will vary from unit to unit, but the instructions provided with your AC unit will normally explain the process. You may have also had specialised equipment provided with your air con — such as vacuum cleaner attachments.

Well known brands will generally also have the instructions available online, and may also have instructional videos explaining how to clean the filters — such as this “How to” video. This can be very handy if you bought a house with aircon already installed, and the instructions were not provided.

How often the filters will need cleaning can depend on factors like how often the split system is run, and if it’s in a quiet bedroom or a busy common area. But generally, cleaning your filters every three to six months is a smart idea.

How often does a split system need to be serviced?

Many manufacturers recommend having your split system serviced every six months to keep them operating efficiently, but this is pretty cautious. As a general rule of thumb, having your AC serviced once a year will generally keep your split system working smoothly without costing a fortune.

How much does it cost to service a split system air conditioner?

The price of servicing an air conditioner varies from company to company, but generally servicing your split system will set you back around $100-$200, depending on the company and how comprehensive their service is (i.e. exactly what they’re checking). It’s worth doing your homework before hiring someone, and making sure they have a good reputation — just as you would when getting your car serviced.

If getting your aircon serviced seems like an unnecessary expense, remember that it generally pays for itself. Regularly serviced split systems run more efficiently (so they cost less), last longer, and are much less likely to break down — so you pay less in the long run by looking after your system.

For reference, REQ’s split system aircon service will cost you $180, and any small repairs needed are included in that fee. If it turns out you need any larger repairs, we’ll waive the servicing fee so you only pay for the repair. Just something to think about.

How long will a split system air conditioning unit last?

The life of a split system can vary greatly with factors like the quality of the unit, how frequently it’s used, and how well it’s maintained. Broadly speaking, you should expect to get around 7–12 years of regular use out of a split system, provided you’re looking after it.

Of course, it’s not unusual for a split system AC to last longer than that. But you may find over time that the unit is losing efficiency — meaning it doesn’t cool as well, and it burns more electricity (making it more expensive). It can also be harder to get parts for very old models, meaning repairs could be more expensive.

Although replacing your split system after a decade or so might seem expensive, the amount you can save on power bills with an aircon unit that’s working efficiently is pretty substantial — so the unit can often pay for itself in reduced energy costs over a few years.

Conclusion

Split system air conditioners are a very common sight in Australia, where aircon is less of a luxury and more of a basic necessity. They’re relatively cheap to install, can be adapted to many home layouts, and excellent at cooling (or heating) a single room or small living area.

They aren’t suited to every household or situation, and normally give way to ducted systems when it comes to heating and cooling an entire house. But they are an incredibly versatile, affordable, and practical option for air conditioning your home.

Article by Lochy Cupit