Modern windows rely on a wide array of technologies to achieve a level of energy efficiency as high as five times that of traditional windows. All that technology can also be confusing. Terms like “low-E glass” and “argon gas” don’t mean much to the average consumer. Any firm making a presentation to you about windows is likely to use dozens of such terms.
Fortunately, there is a simpler way to evaluate different windows.
An organization called the National Fenestration Ratings Council (NFRC) has developed a rating system based on the U-factor. Most windows now carry this rating so it’s becoming easy to make comparisons. You want the lowest U-factor possible. Here are some typical U-factor ratings:Window Type U-factor