WHAT SIZE AIR CONDITIONER

1.   The room opposite is 12m squared
2.   12m x 140 Watts = 1680 watts
3.    We need 1680 Watts minimum to cool this room
4.    2000W is the smallest unit that will cool this room
5.    Most people use a 2.5kw
   

But if you use an average figure of 140 when multiplying your area, the results should be very close to right. The only thing you have to contend with now is your teenagers turning up the heat in winter while wearing shorts and a t shirt. My advice is to keep the air con and chuck the teenagers, but that’s your call.

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 secret room protected by pivoting door – with an arsenal of automatic weapons on racks. But if its less than 20m2 with windoors and doors or strongroom steel that will close, the Mitsubishi Avanti 2.5 kw or a Pansasonic  CS/Cu 25 XKR is perfect.

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.

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. 

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.

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 also cools it – and sends it back on its way to the first.

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.

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