Q: For a fairly mild climate (I live in Melbourne, Australia: we rarely get to 0C and a few very hot 40+C days a year), is it worth triple rather than double glazed? How do I make the calculation?

A: In a hot climate you need to keep the heat out. In a cold climate you need to keep the heat in. The answer is the same in either climate: insulation and triple-glazed windows. There are examples of how much money you can save by installing double and triple-glazed windows in the book in chapter 3. In more remote places like Australia, the choice of windows is often less than we have in the US or EU. This often makes triple-glazed windows hard to find. I even found it hard to get them in the US, my windows came from Canada. If you cannot get triple-glazed windows I suggest looking for the best low-E double-glazed windows. If you use a low-E 272 coating on the outside and a low-Ei89 coating on the inside you will get about R4 insulation with only the slightest greenish tint. This is as good as a triple-glazed window with i89 on the inside.