What Makes A Window Energy Efficient?

Energy efficiency is all the rage these days. Everything from curling irons to windows has an Energy Star rating for energy efficiency. However, it can be tough to the average person to know exactly what that means and how it affects them. Understanding what makes windows energy efficient is the first step to making a home or business more energy efficient.

Glass and Filler

Not all double- or triple- paned windows are energy efficient. The energy efficiency comes from the filler used between panes of glass. Fillers used between panes of glass are colorless, odorless, and completely harmless. The most common fillers are argon and krypton gas. They are heavier than air and therefore reduce the amount of heat that move in and out of windows. Double- or triple-paned glass with argon and krypton fillers are better insulators than others.

Another important thing to consider with windows is Low Emissivity, Low-E, coating. Low-E is a microscopic, metallic coating applied to the glass. The placement of the Low-E in the glass dictates what it does. External Low-E keeps heat out. Internal Low-E keeps heat in.


The glass isn’t the only area to consider when thinking about energy efficient windows. The materials and construction of the frames and sashes are just as important. Overall, wood, vinyl, and wood clad frames are the most energy efficient materials. Wood is a natural insulating material and is easy to work with. Vinyl can mimic the look and feel of wood without the weathering problems associated with it. Wood clad frames are wood on the inside and aluminum on the outside, providing more weather resistance than wood alone.

It is important for all frame joints to be properly and tightly sealed to prevent air leakage. Windows should clinch tightly closed, again to prevent air leakage.

U-Factor and SHGC Rating

The U-Factor and Solar Heat Gain Coefficient are the values that Energy Star uses to rate energy efficient windows. The U-Factor is the ability of the window to conduct non-solar heat. The lower this number is, the better the window insulates. The SHGC rating is the ability of the window to block sunlight that could add heat. In warmer climates, a lower SHGC rating is better. In colder climates, a higher SHGC rating is better.

Energy Star Rating

Energy Star is a government-backed program designed to help people protect the environment through energy efficiency. The larger purpose of Energy Star is to save the consumer money. Truly energy efficient windows will have an Energy Star rating.

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Peter Wendt is a journalist and environmentalist living in Austin, Texas. With a curiosity for new technology and eco-friendly advancements, Wendt decided to research energy efficient windows. He learned that double-paned, argon gas-filled energy efficient windows helped decrease the amount of energy spent. Wendt found a local Austin provider, and has since realized the positive effect the windows have on his energy bills.

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