Window shopping

Glass and glaze

When shopping for windows, you’ll come across single-, double- and tripleglazed units, which is a fancy way of describing the number of panes of glass that make up the window. More panes equal more energy efficiency. As a rule, never go below double-glazed windows, and choose triple-glazed if your budget allows for it.

Besides the glass itself, many window manufacturers tout special coatings and inert gases that aid in efficiency. Clear glass transmits the most solar energy into a building, and glass with a low-E coating-a microthin finish with metal oxide that reflects a large percentage of heat-allows in heat from the sun and prevents heated or air-conditioned air from leaving the room, much like a Thermos. There are other types of coatings, such as the grey, green or bronze tinting popular on office-building windows. For residential use, low-E is usually the best choice for efficiency and aesthetics. The Ontario building code is now calling for all new windows to have low-E coatings, and, sooner or later, this rule is likely to spread through the rest of the country too.

Double- or triple-glazed windows are made even more efficient with the insertion of an inert gas, such as argon or krypton, between the panes. Both gases are colourless, odourless and non-toxic. Whereas a low-E coating reduces radiant heat loss (from the sun), inert gases reduce heat loss from convective sources (the furnace). Also, like low-E coatings, inert gases reduce summertime heat gain.