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What Do Energy Star Window Ratings Mean? (2024)

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Author Image Written by Jessica Wimmer Updated 04/02/2024

Energy Star labels on windows help homeowners find the most energy-efficient products that meet specific efficiency standards. According to Energy Star, replacing old windows with Energy Star-certified products can lower your household’s energy bills by up to 13%. In our guide, we’ll explain what Energy Star window ratings mean and how to read them so you can find the best windows from top-tier window companies your home.

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What Is an Energy Star Window Rating?

Energy Star is a program run by the U.S. Environmental Protection Agency (EPA) and the U.S. Department of Energy that assesses products’ energy efficiency using standardized methods. An Energy Star-certified window must meet the following criteria:

  • Manufactured by an Energy Star partner
  • Independently tested, certified, and verified by the National Fenestration Rating Council (NFRC)
  • Meets strict guidelines set by the EPA

All Energy Star-qualified windows are independently tested, certified, and verified according to the procedures established by the NFRC. The NFRC is a third-party nonprofit organization that certifies rating and labeling to help consumers evaluate window performance and energy efficiency. 

Energy Star assesses a window’s framing materials, panes, glass type, spacers, and more to determine its energy performance.

Most homeowners know an Energy Star rating label is good, but what do all those numbers and codes mean? Here’s how to read an Energy Star label to find the most energy-efficient windows.


U-factor measures the heat transfer rate and indicates how well the window insulates. U-factor values typically range from 0.25–1.25 and are measured in Btu/h·ft²·degrees Fahrenheit. The Btu stands for British thermal units, the h is height, and the ft is feet. A lower U-factor means better insulation.

Solar Heat Gain Coefficient (SHGC)

This number represents the amount of solar energy transmitted through the window and tells you how well it blocks heat from sunlight. SHGC is measured on a scale of zero to one, though its values generally range from 0.25–0.80. The lower the number, the less solar heat the window transmits. 

Air Leakage (AL)

The air leakage number measures how much air passes through the window. AL is measured in cubic feet of air passing through one square foot of window area per minute. Industry standards and building codes require an AL of at least 0.3 cf·m/ft². The cf·m stands for cubic feet per minute, and the ft is feet squared. A lower value means less air leakage.

Visible Transmittance (VT)

VT measures the amount of light the window lets through on a scale of zero to one. Its values typically range from 0.20–0.80. The higher the number, the more natural light will come through the window. A higher or lower number isn’t necessarily better; it depends on how much light you prefer.

Condensation Resistance (CR)

The condensation resistance score measures how well the window resists water buildup. The CR score is shown on a scale of zero to 100. The higher this factor, the less water buildup the window allows. Avoid windows with a CR score below 50.

Energy Star Ratings by Region

Energy Star window performance ratings vary by region since windows perform differently in different climates. The Energy Star label has a U.S. map shaded in blue to signify which area a window is Energy Star-rated in. The two factors that vary regionally are the U-factor and SHGC.

Here are the U-factor and SHGC scores to look for in each climate zone to ensure a window can sufficiently maintain your home’s temperature.

Northern Climate

  • U-Factor of 0.28 and SHGC over 0.32
  • U-Factor of 0.29 and SHGC over 0.37
  • U-Factor of 0.30 and SHGC over 0.42

North Central Climate

  • U-Factor: Less than 0.30
  • SHGC: Less than 0.40

Southern Climate

  • U Factor: Less than 0.40
  • SHGC: Less than 0.25

South Central Climate

  • U Factor: Less than 0.30
  • SHGC: Less than 0.25

You’ll notice the northern climate has several recommended ranges. This specificity is important for those living in colder climates where insulative windows are crucial. The lower the U-factor, the better the window keeps warm air in and cold air out, so look for a lower U-factor the farther north you are.

How to Choose the Most Energy-Efficient Windows

Some window and glass types are more energy-efficient than others. Keep these tips in mind when shopping for Energy Star-certified windows.

  • Window type: Casement, awning, and picture windows are less susceptible to air leakage than other windows.
  • Number of panes: Double-pane windows are much more energy-efficient than single-pane windows, and triple-pane windows are the most efficient.
  • Frame materials: Insulated vinyl, composite, and fiberglass provide more insulation than aluminum.
  • Glass: The most energy-efficient windows are glass-filled and have a low-emissivity (Low-E) coating.

Are Energy Star Windows Worth It?

Yes, Energy Star windows are worth it. According to the U.S. Department of Energy, counteracting heat loss and gain through windows requires 25%–30% of residential heating and cooling energy. Choosing energy-efficient products helps keep this percentage low, reduce energy bills, and save money over time.

Our Conclusion

Always pay attention to energy performance ratings when shopping for new windows. Energy Star-certified windows are tested and verified with labels that clearly outline their performance in your climate. Though energy-efficient windows are more expensive, you’ll save money on your energy bills because your heating and cooling systems won’t have to work as hard to keep your home comfortable.

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FAQ About Energy Star Window Ratings

What is a good Energy Star rating for windows?

Good Energy Star ratings differ by region: Northern, North Central, Southern, and South Central. Use our guide above to see optimal energy ratings for your zone.

What does Energy Star-rated window mean?

An Energy Star rating label means a window has been tested, certified, and verified for its energy performance by region. 

Are Energy Star windows worth it?

Yes, Energy Star windows are worth it. Heat gain and loss through windows account for nearly one-third of your home’s heating and cooling energy usage. A window with Energy Star certification can dramatically cut your energy expenses over time.

Are Renewal by Andersen windows Energy Star-rated?

Yes. Most Renewal by Andersen windows with select glass options are Energy Star-certified in all climate zones of the United States.

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