Another Aussie checking in, as luck would have it. Air conditioning is not necessary at all, nor is heating for that matter. Sure, there are a handful of days in a year when it would be nice to have some climate control, but you'll get over it. It's not something you need. You'll save a buttload of money by insulating your windows and rugging up in winter and not being fat in summer. Personally, I love the heat. I can't get enough of it. 40oC, 45oC? Bring it on. Also, pro tip as a former electrician: the cheapest way to cool yourself on a hot day by far is a fan. Fans draw so little power that they are classed as lights rather than appliances in a maximum demand calculation. If I were to install any kind of climate control, it would only be a fan.