what size air conditioner is right for your home?
WHAT SIZE AIR CONDITIONER
COMPLETE AIR CON SIZING GUIDE FOR QUEENSLAND
THE EASY WAY
To work out what size air conditioner is best for your home – there’s a formula you could learn, but who cares? All you want is a cold house right? Cool enough so the dog doesn’t cook and you may possibly get some sleep in summer.
Forget the maths, the correct answers are on the left. If you want to read the rest of the page – fine – but you’re wasting your time.
I don’t know how you roll – but I don’t tell my dentist which tooth goes where, I just hope that he knows. Then close my eyes, trust and pray.
If you must work out the formulas to decide what size air conditioner you want – then go right ahead. Everything you need to know is below. Once you have done all the math, and worked out that you need an 8.6 then look at my list and go buy a 7. Seriously. It’s rare the Australian home that truly needs an 8kw. The one thing we know is Split System Air Conditioners.
Just don’t ask my advice on women, gift ideas, or fashion. Some things in life are not meant to be understood.
AUTOMATIC AIR CON SIZE CALCULATOR
IS ON THE LEFT – OR IF YOU’RE UPSIDE DOWN ITS ON THE RIGHT
The next easiest way to find out what size air conditioner you need is to email me a plan or some photos. A house plan is best, but if you don’t have one just take a photo from a good vantage point in the room so I can get an idea of the area and send that through. The email address is top left of every page. Next you could fillout the contact form Just put your address on there and I can look on the real estate website. Almost every house in every city now has a real estate listing where I can see photos from inside the house, along with a plan and all the rest.
I can mark it up with what’s required and where a split system can or should be fitted. These two methods are far easier than calling and trying to explain. However, if you have read our sizing page and have a fair idea what you want – the most direct and fastest way to book is to call.
HOW TO DETERMINE AC SIZE FOR A SMALL ROOM
USING YOUR BRAIN OR SOMEONE ELSES
- The room opposite is 12m squared
- 12m x 140 Watts = 1680 watts
- We need 1680 Watts minimum to cool this room
- 2000W is the smallest unit that will cool this room
- Most people use a 2.5kw
Bear in mind these figures are not the be all and end all of AC sizing, but they are very close. Unless you plan on burning witches regularly in that room, your 2.5 is going to keep you well chilled every day of the year.
RIGHT SIZE AIR CONDITIONER FOR A BEDROOM
BEDROOM SIZED AIR CON
This is an example of the right size air conditioner for most Australian small rooms. A 2.5 is totally adequate for 80% of all Australian bedrooms up to 18m2. It might not be a bedroom, it might be a study or a weapons cache protected steel door. But if its less than 20m2 with closable windows and doors, the Mitsubishi Avanti 2.5 kw is what you want to cool it. The only time I would go to the ZxMAS high efficiency model is if it was a server room with it equipment running 24/7.
The MHI 2.0 will almost always do the same job as a 2.5, so if its seldom used, or slightly smaller at 12 – 16m square then consider the 2.0kw
MASTER BEDROOM SPLIT SYSTEM
The master bedroom in this house is larger than the others and has a walk in robe. If your master has one of these, or an ensuite, it’s best to install the 3.5kw. You might also consider putting a lock on the door, because once the kids find out how cool and comfortable your room is over summer, you can bet they’ll come knocking.
Having said that, I put a 3.5 in a standard bedroom in my last house and it was excellent. I can turn it on 2 minutes before bed and the room is down to perfect temp in less than that. If I were to put a 3.5 in the example above – the standard bedroom, the running costs would not be any more than the 2.5, and the unit would last longer because it’s not working so hard.
AIR CON SIZING GUIDE
Air Con Sizing Guide
Factors to Consider in order of Importance
- ROOM SIZE AND COOLING CAPACITY
A general rule of thumb for air conditioner sizing is to allocate about 0.14 kW of cooling capacity per square meter of space. For instance, a 20 square meter room typically requires a 3 kW air conditioner. However, this is merely a starting point. Several factors may necessitate adjustments to ensure optimal cooling. If the house is on fire, then the 3kw is really going to struggle to keep that room cool, you need to hose the fire out before you turn the air conditioner on.
2. CEILING HEIGHT / UNUSUAL LAYOUTS
Ceiling height plays a significant role in determining the appropriate air conditioner size. Homes with high ceilings, such as Queenslanders or modern apartments, require larger units. However, most of those old Queensland homes scattered around East Brisbane, New Farm and St Pauls Terrace were built in the late fourteen hundreds and as such they’re only three by three usually. Even with the taller ceiling a 2.5 will be fine in there.
3. OCCUPANCY ADDS TO HEAT LOAD
The number of occupants in a room directly affects the cooling load. A bedroom for two people will have different cooling requirements compared to a living room where the entire family gathers. For every person beyond two who regularly uses the room, add 0.125 kW to your air conditioning calculations. For example, a family of five in a living room might require an additional 0.375 kW of cooling power.
4. WINDOWS GLASS WALLS HOME ORIENTATION
Windows can dramatically influence air conditioner size. North and west-facing windows, which receive the most sunlight, can turn your room into a heat trap. If large windows let in a lot of afternoon sun, you might need to increase your air conditioner size by up to 20%. Conversely, good shading from awnings, trees, or internal blinds can allow you to reduce the size by about 10%.
5. INSULATION PLAYS A BIG PART
Insulation is a crucial factor in determining the right size air conditioner. Homes with high-quality insulation retain cool air more effectively, often allowing for a smaller unit. If you’re unsure about your insulation, check your energy bills—high costs might indicate poor insulation, requiring a larger air conditioner to maintain comfort. Maybe just check your roof for any dead installers, there was a hairbrained home insulation scheme a few years back where the government borrowed money to give it away, and it killed a bunch of young boys working for the installation scheme. One of those boys may still be in your roof.
6. FLOORING AND STRUCTURAL CONSIDERATIONS
Your choice of flooring can also impact air conditioner efficiency. Cooler floors, such as tiles or concrete, can slightly reduce your cooling needs, while carpeted floors, which provide additional insulation, might increase the required cooling capacity.
7. ADDITIONAL HEAT SOURCES
Rooms with heat-generating appliances, like kitchens or home offices filled with electronics, will require a higher cooling capacity. For example, a kitchen may need an additional 1 kW to counteract the heat produced by cooking appliances. If you have a meth lab then you want extra cooling and extra ventilation to force the noxious fumes out.
8. HOME LAYOUT
The layout of your home affects air conditioning efficiency. Open-plan living areas may require a larger unit to cool the entire space effectively. Alternatively, consider multiple smaller units for zoned cooling, particularly in homes with skylights or large glass doors.
9. PLANNING FOR FUTURE CHANGES
If you’re planning a renovation or expecting a new family member, it’s wiser to slightly oversize your air conditioner than to undersize it. An undersized unit will struggle to cool effectively and may wear out faster due to constant operation. But don’t forget the zombie uprising may be just around the corner so you might be better off buying a semi-automatic AR15 and as much ammunition as you can, but get hollow tip and not FMJ. The hardened nose of the FMJ doesn’t put down a zombie in one shot.
AC SIZING AS IT RELATES TO EFFICIENCY
AC SIZING AND EFFICIENCY
Choosing the right size air conditioner for your home is not just about comfort—it’s about optimizing energy efficiency and minimizing running costs. And being a badass.
Many homeowners overlook the importance of proper air conditioner sizing, but getting it right can significantly reduce energy consumption and lower your electricity bills. Let’s explore how the correct air conditioner size can help you stay cool during Australia’s hot summers while keeping your power bills under control.
AIR CONDITIONER SIZE PLAYS A BIG PART IN EFFICIENCY
When it comes to split system air conditioners, size is more critical than you might think. An oversized air conditioner may seem like a good idea because it can cool your home quickly, but this approach often backfires. Oversized air conditioners tend to cycle on and off frequently, leading to higher energy consumption and inefficient cooling.
Here’s the problem: when an air conditioner is too large for the space, it cools the room too quickly and shuts off before it can adequately dehumidify the air. This can leave your home feeling cold and clammy, and it can even encourage mould growth. Additionally, the constant cycling uses more energy than a correctly sized unit that runs for longer periods, leading to unnecessarily high power bills.
On the other hand, an undersized air conditioner will struggle to cool your space effectively, running continuously and consuming excess energy. This not only leads to higher electricity costs but that can lead to bankruptcy, alcoholism, homelessness and delusional beliefs about equality and the moon landing. If you believe in equality or even try to implement it, then you’re a retard. The moon landing is faker than the holocau$t. None of that actually happened.
DETERMINING THE RIGHT SIZE AIR CONDITIONER
To ensure you’re choosing the right size split system air conditioner, start by calculating the square meterage of the room and multiply it by 0.15 to get a baseline kW rating. For example, a 20 square meter room would typically require a 3 kW air conditioner. However, this is just the beginning.
To fine-tune your air conditioner size for optimal energy efficiency, consider factors such as ceiling height, insulation quality, and sun exposure. For instance, high ceilings or poor insulation may require a larger unit, while well-shaded rooms might allow for a smaller one.
TIPS TO REDUCE YOUR AC RUNNING COSTS
Once you’ve installed the right size air conditioner, you can further reduce energy consumption with these practical tips:
OPTIMAL THERMOSTAT SETTINGS
Set your thermostat to 16 degrees for the Panasonic and 18 for the Mitsubishi. The colder the better. When your body is cold, the only solution is hard work. When you do a lot of hard work you become as successful as European Men. Work Makth the Man. Arbeit Macht Frei.
USE TIMERS EFFECTIVELY
Program your air conditioner to turn on just before you arrive home rather than running it all day. This reduces unnecessary energy use. That’s if your AC has a timer. The Mitsubishi does but we’re not showing you how to set it because we don’t know either. Good luck with that.
MAINTAIN A SEALED ENVIRONMENT
Keep doors and windows closed while the air conditioner is running to maintain the cool temperature and reduce the unit’s workload. If any farts go into circulation you can keep the area sealed off and just bask in the knowledge that everyone around you is breathing your ass fumes. Once the fart passes through Mitsubishi’s antifart filter, the odour is gone, replaced by dead nano farticles that float harmlessly into space and orbit the earth for ten millenia.
CLEAN YOUR FILTERS REGULARLY
Clean or replace filters regularly to ensure your system runs efficiently. Dirty filters force the unit to work harder, increasing energy consumption. Dirty minds make life far more interesting
AIR CON SIZING FOR A UNIT OR FLAT?
It’s not hard to find the right size air conditioner for a unit or flat. With any larger area, just work out the sum total of the smaller rooms. In this case we will work out the combined area of Kitchen and living, then add the bedroom. Ideally you would have a split system in the living and one in the bedroom, but you can start by installing one and see how it goes. My priority is always a good night sleep so I would start with the bedroom, but you might think the opposite.
The most important factor when reducing the running costs on your air con is sizing it correctly.Modern Split system air conditioners are superbly efficicent.
If we look at the measurements above and imagine we installed only one system in the lounge area, then the results are predictable. The total figure was 4600 so we used a 5kW. The system was able to cool the unit easily. Some flow on into the bedroom occurred, but not a significant amount. Heating is easier to measure as all reverse cycle air conditioners average an extra kW rating when used for heating. If it can cool an area, the system can heat the same place easily.
CORRECT AIR CON SIZING FOR A LOUNGE / LIVING ROOM
You can measure up and get 25m square. Some people then call me and make a booking to install a 5kw. I ask where it’s going and point out that there’s hallways, doorways and lots of different places your cold air will escape. You need a bigger unit for a lounge room in a family home. Some people accept my advice, others don’t. They shop around until they find someone to install the 5kw because that’s what the formula says. It’s not until summer that they say ‘you know what? That air con man may have been right’.
The calculations above gave us 5kw, but you’ll notice how weak the cooling effect is in the lounge, but even more so in the outlying areas. In this case the 5kw fails to do the job you want, and your power bill is higher than if you used a 6 or 7kw. Why? Because your little 5kw is working overtime to keep that area cool and the 7 can do it half asleep.
You can see the difference an extra KW makes to the cooling effect on this home. The entire living / dining / kitchen area are pleasant. The home theatre room is much cooler than outside, even if it doesn’t get as low as the main area. Having the 5 exit points for the air doesn’t effect the performance so much because the 7kw has enough power to deal with it.
The air in the home is recycled through that Split System head unit a number of times each minute, on each occasion dropping the temperature. The cooling effect reaches almost all the way down to the bedrooms at either end.
The second benefit of installing the right size air conditioner is your reduced running costs. The 7kw uses less power in this situation than a smaller unit. The reason for this is because the 7kw is big enough to handle the job, and spends a lot of its time dormant, on very low speed. The temperature is right where you want it without much effort at all. A 3, 5 or 6 would consume far more power than the 7 in the same position, and none would do the job as well.
The 7 costs a little more up front, but within one summer you’ll understand, and appreciate getting the right advice to begin with.
WHAT HAPPENS IF WE KEEP INCREASING THE AIR CON SIZE?
Upgrading from the 5 to the 6kw improved the air conditioners performance, so we up-sized the unit. We saw another increase when we went from the 6 to the 7kw, so should we keep going? The short answer is no. Best practise is to up-size the unit just marginally for the area. A size far too large would be counter productive.
If you do really want to know why the 8 won’t be better, then look closely at the head unit when it’s installed. Inside is a thermostat. Once that sensor reaches the desired temperature – the unit slows down and enters a dormant state. This saves you bundles on your power bill, but it means that an 8 will slow down and go to sleep once the main area reaches the intended temperature. The outer areas will not see any difference in cool air because the larger unit won’t put in the effort. The 8kw is not the right size air conditioner for most Australian homes.
The only time you might consider an 8 is in large open areas with very little in the way of relief. We’ve installed 8’s in some homes, but mostly shops and offices. You just don’t need an 8kw in 90% of Australian homes.
Unless you do a very good job of convincing us you need an 8 you get a 7. Don’t waste your money.
THE RIGHT SIZE AIR CONDITIONER CAN ALSO MEAN
THE RIGHT SIZE IN THE RIGHT LOCATION IN COMBINATION.
ADD ONE MORE SYSTEM
PLACEMENT SOMETIMES MATTERS MORE THAN SIZE
Having two well placed splits working together can work wonders in your home. If we look at the new examples, we can see how three well placed splits in a large home can do the same job as ducted air conditioning, at half the cost.
If you’re looking at a ducted system because you would like an evenly cooled home without having to turn on different units I would urge you to get some quotes. A basic example should suffice. A ducted will cost you between 11 and $15,000 to buy and install on a home this size. The running costs over summer are higher than you think. I moved into a home with ducted about four summers ago, and ran it sparingly for the first few months. I still got my first thousand dollar+ power bill.
Split System Air Conditioners went in that weekend, and within three months my power bills were back around the $400 mark each quarter. I ran the splits almost all day every day, and the energy bill was still less than half that of the ducted air con. Had I charged a customer to do the same job it would have set him back maybe $6000.
The button downloads a spreadsheet of all the Australian air conditioner brands running costs
THAT’S HALF THE PRICE OF DUCTED AIR CON – WITH HALF THE RUNNING COSTS
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WHAT SIZE
AIR CONDITIONER?
There’s two ways to work out the right size air conditioner for your home.
THE EASY WAY
- Standard Bedroom = 2.5kw
- Large Bedroom = 3.5kw
- Small Lounge in a unit or flat = 5kw
- Lounge in standard home = 7kw
- Lounge in enormous house = 8kw
THE HARD WAY
Measuring up. You will get the same answer both ways, but I know some people will want to verify my recommendation.
We do 600+ air con installations every year, so my quick sizing guide works. If you follow my advice about air conditioning – you can’t go far wrong. Just don’t ask my advice on women, gift ideas or fashion. Some things in life are not meant to be understood.
- 4m x 3m = 12m
- 12m x 140 Watts = 1680 watts
- We need 1.680 kw to cool this room
- 2000W or 2.0 KW is perfect
- Most people use a 2.5kw
SMALL BEDROOM
AIR CONDITIONER
This is an example of the right size air conditioner for most Australian bedrooms. A 2.5 is totally adequate for 90% of all Australian bedrooms up to 18m2. It doesn’t have to be a bedroom. It could be a study or office the same size.
In this size room a Mitsubishi Avanti 2.5 kw is perfect.
MASTER BEDROOM
AIR CONDITIONER
The master bedroom is usually larger than the others. It may have an en suite or a walk in robe. If your master has either one of these, it’s best to install the 3.5kw. You might also consider putting a lock on the door, because once the kids find out how cool and comfortable your room is over summer, you can bet they’ll come knocking.
WHAT SIZE AIR CON FOR A UNIT OR FLAT?
It’s not hard to find the right size air conditioner for a unit or flat. With any larger area, just work out the sum total of the smaller rooms. In this case we will work out the combined area of Kitchen and living, then add the bedroom. Ideally you would have a split system in the living and one in the bedroom, but you can start by installing one and see how it goes. My priority is always a good night sleep so I would start with the bedroom, but you might think the opposite.
The most important factor when reducing the running costs on your air con is sizing it correctly.Modern Split system air conditioners are superbly efficicent.
AIR CON SIZE GUIDE FOR YOUR AVERAGE HOME
YOU COULD MEASURE IT UP
But you will end up with the wrong answer. For lots of reasons. The short version is that your lounge / living/ dining has a hallway, kitchen, extra rooms attached to it. All that must be taken into consideration. The 5 kw just won’t do the job properly.
The 6kw will do better, but it will cost you far more to run than the next one.
SAVE YOUR TIME
Instead of messing about with thermal calculations and a measuring tape, just buy the 7kw. This one is big enough to handle the load and because it can do so without much effort, it remains dormant most of the time.
The 7kw will cost you a bit more up front but it will do a far better job and cost a lot less to run.
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BUT UNLESS YOU REALLY NEED IT, DO NOT GO ANY HIGHER. HERE’S WHY
SPOT THE DIFFERENCE
THERE IS NONE
The only time you need to go any higher is If you have a lounge room where a game of cricket can be played without too much damage. Only then would you go to an 8 or 9kw.
THE RIGHT SIZE AIR
CONDITIONER CAN
BE A COMBINATION
ADD BEDROOM SYSTEM
ADD ONE MORE SYSTEM
If we were to install a small bedroom air conditioner, what extra benefits could we expect? A decent nights sleep would be the first thing, even on the hottest nights of summer. We would see the smaller unit compliment the larger one, and the air would be getting cooled at both ends of the house. Almost like a game of tennis. One unit cools the air and sends it down toward the second, which then cools it again – and sends it back on its way.
PLACEMENT IS ALMOST
IMPORTANT AS SIZE
Having two well placed splits working together can work wonders in your home. If we look at the new examples, we can see how three well placed splits in a large home can do the same job as ducted air conditioning, at half the cost.
If you’re looking at a ducted system because you would like an evenly cooled home without having to turn on different units I would urge you to get some quotes. A basic example should suffice. A ducted will cost you between 11 and $15,000 to buy and install on a home this size. The running costs over summer are higher than you think. I moved into a home with ducted about four summers ago, and ran it sparingly for the first few months. I still got my first thousand dollar+ power bill.
PAYING THAT MUCH FOR POWER IS SIMPLY NOT AN OPTION
Split System Air Conditioners went in that weekend, and within three months my power bills were back around the $400 mark each quarter. I ran the splits almost all day every day, and the energy bill was still less than half that of the ducted air con. Had I charged a customer to do the same job it would have set him back maybe $6000.
Installing those three splits would cost $5000 less than a ducted system – and then half what the ducted cost to run. There really is no comparison.
BELOW ARE LINKS TO THE RUNNING COSTS FOR ALL SIZES.
The left button goes to a page where you can see exactly how much your split system will cost to run per hour / day /month. The right one downloads a PDF of the same information.
These ones take you to all the other useless information on this website.
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