Window Efficiency Labels Explained

Project planning
December 18, 2020

Energy-efficient windows can help you save money and keep your home more comfortable. However, selecting the right windows to maximize efficiency, comfort and safety, while getting a look that suits your style can feel like a daunting task.

Luckily, modern windows are labeled with standardized window performance ratings, which can make it easier for you to select products that best suit your home’s needs. Similar to when you shop for a car and read the sticker in the window, you want to become familiar with the labels for window shopping so you feel confident in your decision on which windows to install.

But what do all those window energy ratings systems and labels mean? Don’t worry, once you know what to look for, it’ll be much easier to narrow down your choices.

Window ratings

Window Ratings

The following window ratings can be used to determine the efficiency of various windows—and help you sort through the plethora of options available:

When lower ratings mean better windows:

  • U-Value/U-Factor: U-Value, sometimes called window U-Factor, measures the rate of heat transfer—it tells you how much heat is lost or gained through your window. According to Energy Star, the U-Value of a window can range from .25 to 1.25. The lower the U-Value, the more energy efficient your window is bound to be. If your windows see a lot of direct sunlight, you’ll want to find windows with lower u values.

  • SHGC: The Solar Heat Gain Coefficient measures the amount of solar radiation and heat that your windows allow inside the home. The lower the number, the less radiation. This measurement can range from 0 to 1. If your home sees a great deal of sunlight, look for windows with a lower SHGC measurement.

  • Visible Transmittance: Visible Transmittance tells you how much light is allowed to pass through a window. It’s measured on a scale from 0 to 1; the lower the number, the less light will be allowed in. Depending on where you live and the amount of sunlight your home gets, you may want windows with lower or higher visible transmittance. For example, if you’d like to capture more natural light in your home, look for a window with higher visible transmittance. If you’d like to keep your home cooler in the summer, look for a window with lower visible transmittance.

  • Air Leakage: This measures the amount of air that a window allows to pass through. The lower the number, the more airtight the window. If you live somewhere windy, you might want a lower air leakage rating. Air leakage ratings typically range from 0.1 to 0.3.

When higher ratings mean better windows:

  • DP: Design Pressure tells you how much pressure a window can take before breaking. The higher the rating, the stronger the window. If you live in an area that sees heavy winds, storms, and snow, look for windows with higher DP ratings. The typical residential rating ranges from DP 30 to DP 50.

  • Condensation Resistance: This measures how much moisture is able to build up on the surface of your window. It’s measured on a scale from 1 to 100; the lower the number, the more condensation, which can lead to more window damage (and more maintenance for you). If you live in an area that sees rain and moisture most of the year, you might want to look for a higher condensation resistance rating.

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Window performance ratings

Certification Labels

Certification labels are just as crucial as window ratings; you’ll run into these labels when window shopping, and it’s a good idea to understand how they’re awarded.

  • ENERGY STAR Certification Label: ENERGY STAR qualification is based on U-factor and SHGC ratings. This certification itself doesn’t measure anything. It uses NFRC’s overall window thermal test results to create zones for particular areas in the country; it then recommends U-factor and SHGC values for these areas.

  • NFRC Certification Label: The National Fenestration Rating Council (NFRC) helps consumers compare window performance through various ratings, including U-Factor, Solar Heat Gain Coefficient, Air Leakage, Visible Transmittance and Condensation Resistance. NFRC labels test standards include NFRC 100, 200, 300, 400, and 500.

  • NAMI Structural Certification Label:The National Accreditation and Management Institute (NAMI) is an independent company that inspects and certifies windows, doors, and other products. It provides energy performance ratings based on values including U-Factor and SHGC. A NAMI Certification Label will indicate the standard to which the product was tested; the label should show the name of the manufacturing facility, the grade or performance level that was achieved, the series or model name of the product, and any other important information.

  • American Architectural Manufacturers Association (AAMA) Certification label: This certification requires three tests: Water Leakage, Structural Strength, and Air Leakage. Products that are tested for thermal performance only receive a Silver Certification label, while products tested for structural, air and water performance, and thermal performance receive a gold label.

Not all manufacturers choose to test and certify their products with every organization, and most often opt for one certification over another. However, these four certifications serve as a great starting point during your window shopping.

The two labels you should make sure to find: the Energy Star label and the NFRC label. NFRC provides unbiased numbers for you to use in your decision making process, while Energy Star explains if those numbers meet their standards for superior performance.

Keeping an eye out for these window performance ratings and certification labels can help you make the right decision for your home.

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Now that you know more about window labels and certifications, you’re well on your way to a more efficient and comfortable home. To learn more about energy-efficient windows, check out our Windows and Doors page.