Energy-Efficient Windows: Decipher the Ratings

If you can’t conserve your historical windows, then it’s time to find energy-efficient replacements. And selecting new windows involves industry knowledge. It’s important to get a grasp of the alphabet soup: U-factor, SHGC, air leakage, VT and LSG. Next, when you know all of the various evaluation systems, you may pick windows based on your climate and also the prerequisites for your residence.

But who speeds these items anyway? Can you rely on the manufacturer to be truthful? Just like food labels are tracked by the U.S. Department of Agriculture, window labels are certified by the National Fenestration Rating Council. And all Energy Star windows must get an NFRC label. (Notice, though, this Energy Star bases its ratings only on U-factor and SHGC, which can be explained below.) Windows that don’t have the Energy Star label may or may not be rated; then it’s time to check with the manufacturer.

Studio William Hefner

U-factor: How quickly a window lets nonsolar heat to pass through it. The lower the U-factor number, the more energy efficient the window.

Witt Construction

SHGC (solar heat-gain coefficient): Just how much solar radiation a window allows through it. The lower the SHGC, the less solar heat it transmits, which is great on warm days; the greater the SHGC, the solar heating system it allows, which will be great on chilly days. So selecting the most appropriate SHGC score is dependent upon your climate and the window location and any shading, states the U.S. Department of Energy.

PHX Architecture

Air leakage: The lower the score, the lower air flows.

Cary Bernstein Architect

VT (visible transmittance): Just how much visible-spectrum light transmits through a window. The higher the VT, the observable light. Deciding just how much visible light you need is dependent upon how much daylighting you have and whether you want to decrease glare.

Searl Lamaster Howe Architects

LSG (light-to-solar profit):The ratio between the SHGC and VT, basically how efficient the window is in allowing daylight in, while also blocking heat advantage. The greater the LSG, the more light you get with no side effect of warmth.

Sutton Suzuki Architects

Tell Us: Do you plan to install energy-efficient windows? If so, where and which type?

More:
Replace vs. Restore: The Great Window Debate
Energy-Efficient Windows: Understand the Parts
Contractor Tips: How to Choose and Install Windows
Update Historic Windows to Charm and Efficiency

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