Understanding Window Labels

Ashley Christensen
January 12, 2023

Replacing old windows with new, energy-efficient windows can save you money while keeping your home comfortable all year long. Just because a window says that it is energy-efficient, doesn’t mean that they are all the same. Energy-efficient windows have different ratings, that indicate the level of efficiency that they provide, and as with most other things, some windows will be more energy efficient than others. 

Thankfully, when shopping for new windows you aren’t going to be left in the dark to determine which windows are actually energy-efficient and which ones aren’t. Window manufacturers place a sticker on their windows, that displays all the energy ratings for the specific window, until you learn what all the numbers mean, the label might be a bit confusing. Don’t worry, I’ll help you break down what each number means, to help you make an informed decision. 

Window Ratings

There are different factors that help to indicate the efficiency of the various different windows available to you. For these specific factors, the lower the number the better efficiency the window has. 

  • U-Value/U-Factor: The U-Value, also known as the U-Factor measure the rate of heat transfer. In other words, this number tells you how much heat is lost or gained through the window. According to Energy Star, the U-Value of a window can range anywhere from 0.25 all the way up to 1.25. The lower the number, the more energy efficient the window is. For windows that receive a lot of direct sunlight throughout the day, a window with a lower U-Value will be most beneficial. 
  • SHGC: Solar Heat Gain Coefficient (SHGC), measures the amount of solar radiation and heat that is allowed to pass through your window and into your home. The lower the number, the less radiation enters your home. The SHGC number can range from 0 to 1 the lower the number the better. 
  • Visible Transmittance: The visible transmittance rating tells you how much light is allowed to pass through the window. This rating is also measured on a scale of 0 to 1, with the lower the number, indicating a lower amount of light is allowed to pass through. Depending on where you live, you might want a window that has higher or lower visible transmittance levels. 
  • Air Leakage:  The air leakage rating will measure the amount of air that a window allows to pass through. Typically an air leakage rating ranges from 0.1 to 0.3, with the lower the number indicating a more airtight window. 

While most ratings, you want a lower rating to indicate a more energy-efficient window. There are a few ratings, where a higher number indicates a better window. These two ratings are two such, where a higher number is better. 

    • Design Pressure (DP): This number is an indication of how much pressure your window can take before breaking. A higher rating will indicate a stronger window. Typical residential DP ratings will range anywhere from DP 30 to DP 50. Depending on where you live, you might want a higher DP than in other areas. 
  • Condensation Resistance: This number measures the amount of moisture that is able to build up on the surface of a window. It is measured on a scale of 1 to 100, with a lower number indicating more condensation and a higher number with less condensation. A higher number will indicate less moisture, which then translates to mean less damage and maintenance required on the window. 

Certification Labels

In addition to energy-efficiency labels and ratings, you’ll also come across certification labels as you are window shopping. There are different labels, which are awarded for different reasons. Similar to knowing and understanding energy-efficiency labels is important, so is understanding how certification labels are awarded. 

  • ENERGY STAR Certification Label: The ENERGY STAR qualification is based solely on the U-Factor and SHGC ratings, without actually measuring anything itself. In addition to the U-Factor and SHGC ratings, it will also use NFRC’s overall window thermal test results to create zones for particular areas in the country. Based on the thermal test and zones, it will then recommend U-Factors and SHGC values for the different areas. 
  • NFRC Certification Label: The National Fenestration Rating Council (NFRC), helps consumers compare window performance through various different ratings, such as 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.
  • The National Accreditation and Management Institute (NAMI): NAMI is an independent company that inspects and certifies windows, doors, and other products. NAMI provides its rating based on values including U-Factor and SHGC. A NAMI label will indicate the standard to which the product was tested, 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 relevant, important information.
  • American Architectural Manufacturers Association Certification (AAMA): In order to receive this certification, there are three tests that must be performed: Water Leakage, Structural Strength, and Air Leakage. Products that are only tested for thermal performance will only receive a silver certification label. Whereas, products that are tested for structural, air, water, and thermal performance will receive a gold label. 

While there are these different organizations that offer product testing, not all manufacturers choose to have their products tested and certified by every organization. Most manufacturers will opt for one certification over another, for various reasons. While not every product will have a certification from each of these organizations, knowing about and being aware of the different certifications is good information to have when you begin shopping for new windows. 

The two labels that you should make sure you find on windows you’re considering buying should be the ENERGY Star label and the NFRC label. The NFRC will provide you with unbiased numbers that you can use in your decision-making process. The ENERGY Star label will explain if the numbers meet their standards for superior performance.

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