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February 20, 2024

Decoding Window Ratings: What Do They Mean?

Are you feeling overwhelmed by the sheer number of window ratings out there? You’re not alone. With terms like U-factor, R-value, SHGC, and VT, it’s no wonder many homeowners find themselves scratching their heads when trying to decode these phrases and acronyms. 

But understanding these ratings is crucial when selecting windows for your home. It enables you to assess a window’s energy efficiency, insulation properties, and overall performance, helping you make well-informed decisions about your investment.

Common Window Ratings Explained

Here are some of the most common window ratings and what they mean: 

  • U-factor: The U-factor indicates how well a window insulates. The U-factor scale typically ranges from 0.20 to 1.20. A lower U-factor equals better insulation, which means that the window will help keep your home warmer in the winter and cooler in the summer. Recommended ENERGY STAR U-factor window ratings skew lower for colder climates. 
  • Solar Heat Gain Coefficient (SHGC): The SHGC measures how much solar radiation is admitted through a window. SHGC values range from 0 to 1. Lower values mean less solar heat is transmitted, which can help reduce the need for air conditioning and lower your energy bills. In warmer climates, you might want a lower SHGC to reduce cooling costs. 
  • Visible Transmittance (VT): VT measures how much visible light is transmitted through a window.  VT window ratings range from 0 to 1. A higher VT means more natural light can enter your home, which can reduce the need for artificial lighting and create a brighter, more inviting space.  
  • Air Leakage (AL): The air leakage window rating measures how much air can pass through gaps in the window assembly. AL values are measured in cubic feet of air passing through per minute per square foot of window area (cfm/ft²). A lower AL rating means that the window is less likely to let in drafts and reduce energy loss.  
  • Condensation Resistance (CR): CR measures a window’s resistance to condensation. CR values range from 0 to 100, and higher CR values indicate better resistance. A higher CR is preferable in humid climates or situations where condensation is a concern. 
  • Sound Transmission Class (STC): STC measures a window’s ability to reduce sound transmission. It is especially important in noisy environments. STC window rating values typically range from 25 to 75, and higher STC values indicate better sound insulation. 
  • Outdoor-Indoor Transmission Class (OITC): OITC is similar to STC but focuses on outdoor-to-indoor sound transmission, including traffic and other outdoor noises. OITC values also range from 25 to 75, with higher values translating to better outdoor noise reduction.

Check Your Local Replacement Window Regulations

When considering replacing windows in your home, it’s important to check your local regulations and building codes to ensure compliance with specific window ratings. Some cities and regions require that windows have specific energy efficiency ratings, such as U-factor and solar heat gain coefficient, to meet certain standards for insulation and sustainability. In addition, some areas may have regulations related to the material or construction of house windows, particularly in historic districts or locations prone to severe weather. These regulations are in place to ensure that buildings are constructed or renovated with energy efficiency and safety in mind, which can ultimately benefit both homeowners and the environment.

Find Reputable Window Contractors

Finding reputable window contractors is crucial for ensuring a successful window replacement project. By thoroughly researching and vetting potential contractors, homeowners can feel confident in the quality of work and the experience of the professionals they hire. Additionally, obtaining multiple quotes and understanding the cost of replacement windows can help homeowners make informed decisions and stay within budget. 

For more information on window replacement costs and to get started on your project, visit our page about the cost of replacement windows. There, you can access valuable resources, compare pricing, and find the best window contractors in your area.


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