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Understanding Window Ratings: What Do Energy Star and NFRC Labels Mean?

When it comes to choosing the right windows for your home, understanding window ratings is crucial. Among the most significant ratings you’ll encounter are the Energy Star and NFRC labels. These labels provide vital information about a window’s performance and energy efficiency, helping you make an informed decision. At Diligent Window Supply, located in Baltimore, Maryland, we aim to educate our customers on these essential ratings to ensure you select the best windows for your needs.

The Importance of Window Ratings

Window ratings are designed to help consumers understand how well a window performs in terms of energy efficiency and overall quality. With rising energy costs and increasing awareness of environmental impact, choosing energy-efficient windows is more important than ever. Not only can energy-efficient windows help reduce your utility bills, but they also contribute to a more comfortable indoor environment and a smaller carbon footprint.

Understanding Energy Star Ratings

Energy Star is a widely recognized symbol for energy efficiency, backed by the U.S. Environmental Protection Agency (EPA). Windows that earn the Energy Star label meet stringent energy performance criteria set by the EPA. Here’s what the Energy Star label signifies:

  1. Energy Efficiency: Energy Star windows are designed to minimize heat transfer, keeping your home warmer in the winter and cooler in the summer. This reduces the strain on your heating and cooling systems, leading to lower energy bills
  2. Environmental Impact: By choosing Energy Star-rated windows, you are contributing to environmental protection. These windows help reduce greenhouse gas emissions by decreasing the amount of energy needed to heat and cool your home.
  3. Performance Testing: Energy Star windows undergo rigorous testing to ensure they meet specific performance criteria. This includes testing for air leakage, thermal performance, and condensation resistance.

What Does the NFRC Label Mean?

The National Fenestration Rating Council (NFRC) provides standardized ratings for the energy performance of windows, doors, and skylights. The NFRC label offers a comprehensive overview of a window’s performance, allowing consumers to compare products objectively. Here’s a breakdown of the key components of the NFRC label:

  1. U-Factor: The U-factor measures how well a window prevents heat from escaping. Lower U-factors indicate better insulation and higher energy efficiency. For windows in colder climates, a low U-factor is particularly important.
  2. Solar Heat Gain Coefficient (SHGC): The SHGC measures how well a window blocks heat from the sun. A lower SHGC means the window is better at blocking unwanted solar heat, making it ideal for warmer climates. However, in colder climates, a higher SHGC can be beneficial for capturing solar heat during the winter.
  3. Visible Transmittance (VT): VT measures how much visible light passes through a window. Higher VT values mean more natural light enters your home, reducing the need for artificial lighting during the day.
  4. Air Leakage (AL): The AL rating measures the rate at which air passes through the joints in a window. Lower AL values indicate less air leakage, contributing to better energy efficiency and indoor comfort.
  5. Condensation Resistance: This rating indicates how well a window resists the formation of condensation on its interior surface. Higher condensation resistance is preferable as it helps prevent mold growth and water damage.

Choosing the Right Windows for Your Home

When selecting windows for your home, it’s essential to consider both Energy Star and NFRC ratings. Together, these labels provide a comprehensive understanding of a window’s energy performance and overall quality. Here are some tips for making the best choice:

  • Climate Considerations: Select windows with ratings that suit your climate. For example, in colder climates, prioritize windows with low U-factors and higher SHGCs to maximize energy efficiency and comfort.
  • Home Orientation: Consider the orientation of your home. Windows facing south or west may benefit from lower SHGCs to minimize heat gain, while north-facing windows may prioritize higher VT for natural light.
  • Professional Consultation: Consult with window professionals, like the experts at Diligent Window Supply, to understand which ratings are most important for your specific needs and to ensure proper installation for optimal performance.


Understanding window ratings, particularly Energy Star and NFRC labels, is essential for making informed decisions about window purchases. These ratings provide valuable insights into a window’s energy efficiency and overall performance, helping you choose products that will enhance your home’s comfort, reduce energy costs, and contribute to environmental sustainability. At Diligent Window Supply in Baltimore, Maryland, we are committed to helping you navigate these ratings to find the perfect windows for your home. Visit us today to explore our wide range of high-quality, energy-efficient windows.

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