THE RIGHT SIZE AIR CONDITIONER
The easy way to measure a room or a whole houseGet the right size air conditioner for your home
THE RIGHT SIZE
AIR CONDITIONER
FOR YOUR HOME
To determine the correct size air conditioner you’ll need just measure the room. Doesn’t have to be exact.
Measuring a room for the right size
- Simply multiply the (L) length by the (W) width
- 4m x 3m = 12m
- Then : 12m x 140 Watts = 1680 watts
- We need 1680 Watts minimum to cool this room
- 2000W or 2.0 KW is perfect
- Anything less than 1680 Watts will not cool this room effectively
- Simply multiply the (L) length by the (W) width
- 4m x 3m = 12m
- Then : 12m x 140 Watts = 1680 watts
- We need 1680 Watts minimum to cool this room
- 2000W or 2.0 KW is perfect
- Anything less than 1680 Watts will not cool this room
The above multiplier is accurate for weather patterns in Brisbane, Sydney, and Perth. Standard roof height is assumed of 2.4m. Standard window sizes and no extra sources of heat. If you lived closer to the equator the multiplier would increase. Example : for the same room in far north Queensland you might use 12 x 180 = 2160 watts for other size calculators see other sizing guides. When measuring larger areas above say 6000W this should only serve as a guide. As a general rule, an Australian home needs a 7kw in lounge and 2.5 in bedroom. That’s your answer in 90% of cases if you don’t want to read the rest of the page.
CORRECT SIZE AIR CONDITIONER FOR A BEDROOM
Bedroom split system
This is an example of the right size air conditioner needed for most Australian small rooms. A 2.5 is totally adequate for 80% of all Australian bedrooms up to 18m2. In this size room a Mitsubishi Avanti 2.5 kw or a Pansasonic CS/Cu 25 VKR is perfect
Master bedroom split system
The master bedroom in this map isn’t much bigger than the other bedrooms. A 2.5 would be adequate in this diagram also. Under normal circumstances, in a master bedroom with a walk in robe or an ensuite, you would install a 3.5kw Mitsubishi or Panasonic
WHAT SIZE AIR CONDITIONER FOR A UNIT OR FLAT?
THE RIGHT SIZE AIR
CONDITIONER FOR
A UNIT OR FLAT
A unit or flat isn’t much harder to size. 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. The bedroom can’t be measured because very little air will filter through. You will get some residual cooling effect, but only the main space where the air conditioner will be mounted – should be calculated for cooling watts.
The results are predictable. Because our figures gave us 4600 and we used a 5kW, the unit was able to cool the entire units living space 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. Basically if it can cool an area, it can heat the same place easily.
DON’T OVER COMPLICATE THINGS
SIMPLE SOLUTION
FOR 90% OF
AUSTRALIAN HOMES
As a general rule, for an Australian home a 7kw in the lounge and a 2.5kw in the bedroom is perfect. It’s very rare that we find a home where this combination won’t be effective. Perhaps if you have a very large master bedroom or high ceilings then a 3.5kw. If you order off us and we arrive to find it’s not right or a different combination would work better, we will advise you before we do anything. We won’t just put it in because we are there.
Many calls each summer come in using the calculations above and are convinced they need an 8kw or 9kw unit. It’s rare the Australian home that requires anything bigger than a 7kw in lounge. The 140x multiplier is accurate at smaller sizes, but when calulating larger areas things like windows, sunlight hours, upstairs / downstairs play a larger role. Unless you do a very good job of convincing us you need an 8kw you get a 7. Don’t waste your money.
COOLING THE MAIN AREA OF AN AVERAGE HOME
An area is only a total of the room sizes. Panasonic sizing guide here
COOLING THE MAIN
AREA OF AN
AVERAGE HOME
- To determine the right size air conditioner
- we simply break it into 2 parts
- Section 1 is 8 x 3 metres (24)
- Section 2 is 5 x 3 metres (15).
- Total of 24 + 15 = 39 metres squared.
- 39 x 140 = 5460 watts. You need a 6kW unit minimum.
However in this case, you have a hallway, a kitchen and a messy teenager who absolutely will run this unit on heating in winter while wearing a t shirt and shorts. Let’s take a look at how different size units would cope with this area.
RIGHT SIZE AIR CONDITIONER FOR THIS HOME
CORRECT SIZE
AIR CONDITIONER
FOR THIS HOME
Examples of four different sizes and their cooling effect on the home :
Example of 5kw Cooling
What’s the perfect size air conditioner to use in this home ? The ideal method is by placing a large unit in either of the two marked dark blue positions. The two locations in this example won’t have much different results. An air con works by circulating all the air in a given space, not just by blowing cold air in one direction. We will start by illustrating a 5kw cooling pattern. In this case the 5kW is not the right size air conditioner, it would struggle because the area is too large and have a considerably shorter lifespan due to working so hard.
Example of 6kW cooling
This main living area would be adequately cooled by a 6kW system Easily reaching to all corners of the main 3 living spaces, the 6 in this example is far superior to the 5. It will easily keep the whole area at an even temperature on the hottest day, and the machine won’t be working overtime to keep it there. We do have a hallway which will allow a lot of air escape, meaning the 6 would use more power over time to keep your living space at the desired temperature. Let’s look what happens if we go just one more size increase up.
Example of 7 kW cooling
The right size air conditioner for here is a 7kW. Our calculations from example two gave us 5400 odd watts. However : that figure is the minimum required cooling power for the given area. The 6kW as set out above would cope fine with the cooling load, but what other considerations are there? Energy consumption is one, future expansion maybe another. If you look at the pattern illustrated, the 7kW won’t cool the far bedrooms noticeably at all, but what if we wanted to cool those in future?
Would we go up to an 8? The short answer is no. Slightly over sizing a unit is good practice, but any further size increases (past 7) aren’t needed. As shown in next section.
Example of 8 kw Cooling
Notice the similarity to the 7. Installing an 8 or larger in our area will not help. Any temperature under 18 isn’t comfortable anyway. In this case, the 7kW (above) is ideal for the area we have. If you wish to have a greater cooling effect, or a more energy efficient climate, then a combination of units is what you require.
An 8 kW+ is a very powerful machine. Best suited to large open areas. The air flow range and power difference between an 8 and a 7 is substantial, but would only really take effect in a large open area that would suit the 8.
BIGGER IS NOT
ALWAYS BETTER
BIGGER IS NOT ALWAYS BETTER
Instead of just buying the biggest unit you can get, sometimes the answer to what size air conditioner is: where you put the right size air conditioner.
LOCATION IS MORE IMPORTANT
If you look again at the 4 examples above, what did you notice about the last two? The far right 8kW isn’t much cooler than the 7kW overall ..Despite having an extra 1000 watts of cooling power, the far rooms didn’t get a great deal extra. The reason is that the thermostat to control the units behaviour is mounted in the head itself, so once the main room reaches desired temperature, the unit will ramp down. There is no way to overcome this issue without running up your power bill very very high, and unnecessarily.
See Ergon Energy Air Conditioner running costs page
A GOOD NIGHTS SLEEP IN
AN AIR CONDITIONED ROOM
A GOOD NIGHTS
SLEEP IN AN AIR
CONDITIONED ROOM
If a good night’s sleep is important to you then I would suggest installing a bedroom unit first. It’s always highest on my priority list. The main room comes next. However if we did them together, we could cool the whole house more evenly, use considerably less power than an 8kw and be able to operate them independently. Here, clearly the answer to what’s the right size air conditioner is : the right size and right location.
For a guide to the best temperature for the perfect nights sleep
Now we know the right size is air conditioner (s) to use, where will we put it? More importantly, where can we put it? See the A.C.Expert easy location guide.
You can see the air conditioner price list or examples of our fine installations.