Argon can help keep your home warmer

The summer of our discontent has made for a glorious winter. While the rest of the country seems to have been beset by winds, floods and even tornadoes, "winter" in Dunedin has been a succession of relatively warm, cloudless days, as evidenced by my kowhai flowering in early July. Even the polar blast of a couple of weeks back hit Christchurch harder than here.

This, of course, has not been good news for sellers of heat pumps, wall, floor or ceiling insulation and double-glazed windows.

And it's the latter I want to focus on today.

I have a theory as to why New Zealand houses are renowned the world over for being so damn cold inside.

It's that, with very few exceptions, no part of New Zealand really gets so cold that you're going to die in your house if the heating goes off. Sure, it might be uncomfortable, but not lethally so. I spent a year in Minnesota a while back. It gets cold there - so cold, in fact, that the electricity companies are not allowed to cut off your electricity from the months of October to April if you don't pay your bill, because you undoubtedly would die.

Thankfully, New Zealand is now seeing sense and all new homes are required to have some decent standard of insulation. The main avenue of heat loss in a house (if you believe those ads on TV) is through the windows, so double-glazing or even triple-glazing is becoming more popular.

The very latest in insulated glass units (IGUs) features windows in which the voids between panes are filled with argon, which is supposed to reduce heat loss even more than the cheaper air-filled IGUs.

Argon is an example of what we chemists call a noble or inert gas, for the very reason that it doesn't react with anything. It lives in Group 18 of the periodic table of the elements, along with its similarly inert chemical cousins helium, neon, krypton, xenon and radon.

Like all these elements, argon eluded discovery for many years because of its inertness, and was in fact one of the last of the naturally-occurring elements to be discovered, in 1894. This is despite the fact that it's the third most abundant gas, after nitrogen and oxygen, in the air that we breathe (about 0.9% by volume). Indeed, it was first isolated by the distillation of liquid air at very low temperature.

Argon finds use in modern architectural IGUs because it is a poor conductor of heat. This is, at least in part, due to the fact that argon is heavier than oxygen and nitrogen. In order for a gas to conduct heat, its constituent atoms or molecules must collide with each other - the more rapidly they move, the more energetic are the collisions and the better the gas is at conducting heat. Because argon atoms are relatively heavy, they move more slowly than molecules of nitrogen and oxygen and, therefore, argon is a fairly good insulator.

Using this reasoning, krypton, xenon and radon would work even better in double-glazed windows because they are heavier again than argon, but they are much more expensive.

The fact that radon is radioactive would hardly be a good selling point.

Ideally, it would be optimal to have nothing in the voids - a vacuum - but while such windows do exist, they have been known to implode occasionally.

So, whether or not you have argon-filled IGUs, make the most of this beautiful clear winter weather while it lasts - for remember, summer is fast approaching ...

• Dr Blackman is an associate professor in the chemistry department at the University of Otago.