Decoding Energy Star Ratings: What Do They Mean For Your Windows?

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How does your window’s energy efficiency stack up? Let’s talk Energy Star ratings. 

It almost doesn’t need to be said that energy efficient windows are important. So important, in fact, that Energy Star was established in 1992 by the EPA in order to rate energy efficient appliances and reward homeowners who choose to use them. Energy efficient help conserve the environment, as well as save homeowners money every month on their energy bills. 

When you search for energy efficient replacement windows, Energy Star ratings can help you to understand exactly what you’re getting from them. But first, you have to understand what the window’s Energy Star rating means. 

Energy Star’s Rating System

Energy Star scores, energy efficient appliances on a scale of 1-100. Much like a school grade, the higher your energy score, the better. This evaluates energy performance based on billed energy usage. Because of this, this rating scale is usually used for broader energy efficient ratings, such as an energy efficient rating of a building as a whole, rather than energy ratings for a particular window. This comes most in handy when having a home energy audit. But if you need a rating for windows in particular, Energy Star’s website directs you to the windows National Fenestration Rating Council (NFRC) label.

NFRC Label

Your window’s NFRC label is based on four different criterias: U-Factor, Solar Heat Gain Coefficient (SHGC), Visible Transmittance and AIr Leakage. 

  • U-Factor measures the window’s ability to keep heat from escaping a room on a scale of 0.20 – 1.20. The lower the number, the less heat escapes the room. 
  • SHGC measures a window’s ability to resist heat gain from outside on a scale of 0-1. The lower the number, the less heat gets into the room. 
  • Visible Transmittance rates the amount of light that the window lets into the home on a scale of 0-1. In this case, the higher the number, the better. 
  • Air Leakage measures the amount of air that leaks into the home through the windows on a scale of 0.10 – 0.30. The lower the number, the stronger the air seal for the home.

These ratings are easy to understand and keep in mind as you consider your replacement window options, but they don’t exist inside a vacuum. You also want to think about the climate in which you live when judging the importance of these ratings.

Climate Differences

Milwaukee’s climate is very different from San Francisco’s climate and calls for very different energy performance from its replacement windows. Here again, Energy Star’s website has a helpful guide, breaking the US map into four different regions. Wisconsin is in the Northern region, so it tends to be cooler on average than other regions of the United States. For this reason, any SHGC rating can still be considered energy efficient, because there’s less threat of unwanted heat gain. In fact, SHGC should probably be no higher than 0.42. However, U-Factor is important during Milwaukee winters, and windows must have a U-Factor of at least 0.27 to be considered energy efficient. If you’re in the market for energy efficient windows that are truly air sealed and get the Energy Star seal of approval, contact Homesealed Exteriors today for a free estimate. We carry high quality Okna and Hi-Mark windows with an air leakage rating of .01, literally the lowest the rating can be and still be measured.

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