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Decoding Window Labels

Courtesy of City of Roseville CA.
By Gates Dearen
If you have been considering upgrading your home’s windows, you may have noticed that there are a great variety of replacement window options.  Perhaps you have taken the time to visit the showroom of a company that specializes in replacement windows.  If you did, one of the first things you probably noticed is that every window you were shown had a label affixed to it containing information about U-Factor, Solar Heat Gain Coefficient, and Visible Transmittance.  The label might as well have been written in hieroglyphics for all the good it did you.  As a result, you may have left the showroom more confused about replacement windows than you were before you set foot in the store.  To help you navigate your way to choosing the right windows for your home, I have taken the time to help you decode the information presented on window labels.

What’s It All About?
To protect consumers, the US government has tasked the National Fenestration Rating Council, otherwise known as the NFRC, to regulate, monitor and categorize windows sold in America. More importantly, it also requires manufacturers of replacement windows to include an NFRC label on all windows, doors, and skylights they make.  The reason this requirement was mandated, was to help consumers make an informed decision about any window or door they are considering.  The only problem with these labels is that unless you work in the replacement window industry, it can be confusing. Ultimately, there are really only seven things the label reveals: Description, Heat Transfer, Radiant Heat, Light Transmission, Air Leakage, Water Tightness and any Certifications the window has been given.

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This block of information tells you who manufactured the window, the type of window and the number of panes (single, double or triple glazed). It also tells you about the material used for the frame (aluminum, fiberglass, vinyl, or wood), the mode of operation (casement, double-hung or sliding), as well as any inert gas or window coating used to enhance performance. 

Do You Know U?
U-factor is the first of 3 energy ratings the NFRC bestows on windows.  Ranging from 0.02 to 1.20, this rating is an indicator of how well the window prevents heat from passing through it.  Unless otherwise noted, the rating includes the entire window, including the frame, the spacers, and the glazing. Center of glazing U-factor is sometimes mentioned.  This value designates the performance of the glazing alone.  Either way, the lower the U-Factor, the better it's insulating value.

Solar Heat Gain Coefficient
The SHGC is another energy rating that relates to how well a window keeps out the elements, in this case, heat gain caused by direct exposure to sunlight.  The SHGC includes the window and the frame.  If the label designates the center-of-glass SHGC, this rating only includes the glazing. Ranging from a low of 0 to a high of 1, just as with the U-Factor, the lower the number, the better the rating.

Visible Transmittance
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Just as with the SHGC, Visible Transmittance shows how well the window deals with the Sun.  In this case, the rating isn’t concerned with heat transfer, as much as it is concerned with the transmission of visible light.  While visible light doesn’t add to or detract from the energy efficiency of a window, it will affect how much sunlight is let into a room.  Ranging from 0 to 1, the lower the VT rating, the less visible light is allowed in.  The trick is to balance a window’s VT and SHGC so that solar heat gain is limited without keeping you in the dark.

Air Leakage
Since most homeowners replace their existing windows to reduce the leakage of air conditioned or heated air, one of the key factors to choosing windows that can keep the elements at bay is by determining how much energy can be lost through cracks in the window assembly.  Just as with the U-Factor, SHGC and VT ratings, the closer to 0 the more airtight the window.

Condensation Resistance
If you have ever awakened in the morning to find a mist of water on the inside of your windows, then you have experienced this factor in action.   The CR rating measures how well a window resists the formation of condensation inside the home.  While not an energy hog like some of the other rating factors, who wants to have water intrusion eating away at the windowsill?  Ranging from 0 to 100, the lower the number, the less interior condensation will form.
While most folks have heard of the Energy Star certification, many consumers don’t really understand what it means.  The Energy Star logo is meant to inform you that the window you are considering exceeds industry standards when it comes to providing consumers with exceptional energy efficiency.  The map that accompanies the logo designates the geographic area to which the certificate is valid.
There are a couple of other certifications that can be included on a window label such as Hallmark Certified and the Window and Door Manufacturers Association certificate.  Just as with the Energy Star label, these certificates designate high standards of manufacturing excellence.
If you are considering replacing any of your windows or doors, please contact me at HomeRite Windows and Doors in Jacksonville.  
HomeRite is a window and door dealer that specializes in energy efficient, quality products with warranties and service to match. The company has been in business since 2005. HomeRite is partnered with a manufacturer that has been producing high-quality products and providing excellent customer service for over 60 years. Windows and doors from HomeRite are some of the highest quality, most thermally efficient windows and doors on the market.

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HomeRite products add substantial value to their clients’ properties. HomeRite is a member of the United States Green Building Council, a non-profit organization comprised of leaders across the industry working to advance environmentally responsible buildings.

Gates Dearen is the co-owner of HomeRite Windows and Doors in Jacksonville, FloridaHe and Richard Walden have been serving the building products industry in Florida for over 25 years. They strive to match homeowners with the right windows and doors for their homes and budgets. They make the home improvement process pleasant with first-rate, energy-efficient products, affordable pricing, and award-winning installers who employ the best practices and who always treat customers and their property with the utmost respect.


  1. This article makes it easy to understand window labels. Thanks! :D

  2. It's amazing that the feds mandate manufacturers provide information about their products on the label, then make the info so arcane that nobody except those in the industry can under stand it. Thanks for the translation.