This article will teach you how to take advantage of energy rating on your homes windows by understanding and utilizing the information regarding your homes zone rating, the window warranty, and the window efficiency claims.
The most information regarding the effects of energy loss, heat loss, and solar reflectance for your windows is located on the NFRC label, like the image below. The NFRC (National Fenestration Rating Council) label illustrates the test results from an independent testing laboratory which will enable you to compare and understand the performance of your windows and a potential window replacement. While, independent testing results are not required by law from window manufacturers and installers, the majority of large residential and commercial window suppliers subject their products to this level of scrutiny.
Therefore, the NFRC label is both your assurance that your windows meet specific energy regulations and a comparison tool to identify the replacement window for your need. The test and rating scale for NFRC labels is displayed below.
Energy Star: The shaded potions of the map show where a window meets Energy Star criteria. This unit passes muster nationwide.
Visible Transmittance (VT): Specifies how much light passes through; 0 is opaque, 1 is transparent. Glass with a VT of .60 or more looks clear. A VT below 0.40 gives things a grayish cast.
U-Factor: Measures how effectively a window stops heat flow. The smaller the number, the better the performance.
Solar Heat Gain Coefficient (SHGC): Indicates the ability of the glass to block the sun’s heat. The lower the number, the less heat gets in. In the northern zone (see map below), an SHGC of 0.32 or more can offset less-than-ideal U-factors up to 0.30.
Know Your Energy Rating Zone
In many instances, two windows that look exactly the same may not perform exactly the same. In short, not all windows are created equally. The differences between two identical windows can be seen more visibly by differences in the energy efficiency ratings. The Federal Law dictates specific efficiency ratings based on your geographic location. Below is a map which dictates the minimum level of efficiency based on your location in the United States.
Perhaps the most important take away from this article should be that the minimum energy rating for your windows IS NOT the recommended rating.
Colder climates such as the Midwest (Wisconsin, Minnesota, Illinois) it is recommended to have at least triple pane glass windows with a high solar reflectance rating (U factor) to offset the costs associated with cold winters and hot summers.
Think of your windows as an investment, and with any investment consider the window and glass package that best fits your homes needs.
Energy Saving Tips
Try these tips for enhancing the performance of your window by improving the glass and insulation.
Low-e coatings: These transparent, micron-thin layers of metal reflect heat either toward the interior (in cold climates) or toward the exterior (in warm ones), depending on the glass surface they’re fused to. The can reduce heat loss (or gain) by as much as 35 percent, per information from the U.S. Department of Energy.
Inert gases: Air trapped between panes insulates fairly well, but if a gas such as Argon is used instead, performance improves by 16 percent. Xenon and krypton insulate even better than argon. These heavier gasses will improve the R-Value of your windows by at least 0.5 points.
Warm-edge spacers: Standard aluminum spaces conduct lots of heat through the edges of double-pane glass. Nonmetallic, warm-edge spacers bring those loses down by 10 percent, per Cardinal Glass, and make it more difficult for condensation to corm on inside panes.
For more information on why to replace your windows read more here.