The mystery of window labels

As if there wasn’t enough confusion when you are selecting windows for your home, the window labels come in. When comparing the incredible number of options that are flooding the market, NFRC (National Fenestration Rating Council) actually comes to the rescue with its energy performance labels – if you know how to read them, of course.

It’s not the only thing to consider when selecting a window, but it’s important, so here we go.


This indicator provides you with the window’s heat transfer rate, which informs you about how well the window will perform in the cold season, insulating your house from the elements. The value may vary in the range between 0.25 and 1.25, with lower values meaning better insulation. There is also information on recommended U-Values for various climates.

Visible Transmittance

Gone are the times when glass was just glass, now even the degree of how much light is allowed to pass through. It’s become very important when windows are routinely made with two and three panes of glass, which makes them highly energy efficient, but allows less light through.

Solar Heat Gain Coefficient / SHGC

This parameter is important in warmer climates, and it indicates how efficient a window is in blocking sunlight heat, keeping your house cool in the summer. This indicator value ranges from 0 to 1, and a lower value indicates less solar heat transmission. Once again, there are SHGC recommendations for various regions. Besides the climate, the orientation of the window also has a lot to do with what SHGC value you should choose, i.e. west-facing windows a low value is preferable, while for south-facing windows it’s better to choose a higher coefficient, so that during cold season more heat would naturally come inside.

Different combinations of these three factors should be considered in relation to the climate and the particular needs of your home. A good balance may be difficult to achieve, but with the range of available options there’s a perfect chance you’ll come out with a perfect combination. If you need some expert advice – we’ll be happy to help. We’ll help you choose the right window, and help you maintain and fix windows as needed.