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The right size Air Conditioner

The easy way to measure a room or a whole house

Get 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

  1.    Simply multiply the (L) length by the (W) width
  2.    4m x 3m =  12m
  3.    Then : 12m x 140 Watts = 1680 watts
  4.    We need 1680 Watts minimum to cool this room
  5.    2000W or 2.0 KW is perfect
  6.    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 effectively
right size air conditioner calculation drawing at air conditioners brisbane

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.

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 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 CS/Cu e25 TKR is perfect

As of 2018 there are other options. We can now install a 1.7kw or 2.0kw MHI which will easily take care of this sized room. See prices page for new size prices

 

2kW split system coverage choosing the right size air conditioner

Master bedroom split system

The map we used here isn’t ideal as the master bedroom doesn’t have a walk in or ensuite which are common today. Even this sized bedroom would be adequately serviced by a 2.0 or 2.5kw unit.

The reason we have upped the size by one is explained further down. As a general rule most bedrooms are fine with a 2.5, but when a walk in or ensuite is present go to the 3.5kw.

3.5kW split system coverage choosing the right size air conditioner
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What size air conditioner for a unit or flat?

The right size

air conditioner

for a unit

or flat

plan of unit for right size air conditioner page

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.

5kW split system coverage choosing the right size air conditioner

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 Panasonic 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.

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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.

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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
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The 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.

 

5kW split system coverage choosing the right size air conditioner
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. 

6kW split system coverage choosing the right size air conditioner

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.

7kW split system coverage choosing the right size air conditioner

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.

 

8kW split system coverage choosing the right size air conditioner
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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. 

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

8kW split system coverage choosing the right size air conditioner
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

7kW with 2kW split system coverage choosing the right size air conditioner

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.

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