By Rob Fanjoy
Windows have certainly changed over the years. We are almost at a point where windows that can actually respond to environmental conditions on their own (changing tints or producing heat via specialty coatings and electronic charges, often called electrochromic or thermochromic windows) will be widely available.
It used to be that low-E coatings were a custom option and came at a price premium, but over the last five years or so they have become standard in many markets. The next energy-efficient window element to jump into the Widespread Use line is the use of gas fills.
By removing all air from between the panes of glass in an IG (insulated glass) unit, and then filling that void with an inert, odorless and non-toxic gas — typically argon or krypton — a window's overall energy performance is greatly increased. The gasses have a higher resistance to heat flow than air, reducing the conduction of heat between panes of glass and improving a window's U-factor — the rate at which the window conducts heat other than sunshine.
These gasses have had a reputation of leakage, but several recent studies suggest only a 10 percent loss over 20 years, which reduces the window's effectiveness by only a small percentage. And these gasses are present in normal air, so they are perfectly safe. Still, when selecting and installing gas-filled windows, make sure the manufacturer's sealing methods meet with your approval.
Specifying low-E coatings and gas fills adds about 5 percent to the window's total cost, which can add up on a big job with many large specialty windows. When customers consider the reduced energy bills and added comfort they'll enjoy, that added cost will seem pretty minimal.
Rob Fanjoy is a freelance writer and former editor of Smart Homeowner magazine. He is currently updating his own Michigan home with energy efficient features.
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