The Energy Star label on a window is evidence that it’s an energy-efficient product that meets certain efficiency standards. Energy Star-certified products can lower your home’s energy bills by up to 13%, and homeowners that want to cut costs and become more environmentally friendly should consider investing in certified windows. Read our guide below to learn how to read an Energy Star rating, the benefits of certified windows, and how to decide whether these products are worth the cost.

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What Is an Energy Star Window Rating?

The United States Department of Energy and Environmental Protection Agency use Energy Star as a means to assess the energy efficiency of different products. An Energy Star-certified window must meet the following criteria:

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

All Energy Star-qualified windows are independently tested, certified, and verified according to the NFRC’s standards. The NFRC is a third-party nonprofit organization that helps consumers to evaluate window performance and energy efficiency. 

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

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How To Read an Energy Star Window Rating

Most homeowners know an Energy Star rating label is good, but the more specific elements of a label can be confusing. Follow the steps below to decode a rating:

U-Factor

A window’s U-factor measures the heat transfer rate, and indicates how successfully a 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 indicates better insulation.

Solar Heat Gain Coefficient

This number represents the amount of solar energy that transmits through a window. It spells out how well a window blocks the sunlight’s heat. SHGC is a number between 0 and 1, and its values generally range from 0.25–0.80. The lower the number, the less solar heat the window transmits. 

Air Leakage

The air leakage number measures how much air passes through a window. AL is measured in cubic feet of air that passes 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. A lower value means less air leakage.

Visible Transmittance

VT measures the amount of light the window allows 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 can come through the window.

Condensation Resistance

The condensation resistance score measures how successfully the window resists water buildup. The CR score is a score between 0 and 100. The higher this factor, the less water buildup the window allows. Avoid windows with a CR score below 50.

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Energy Star Ratings by Region

Energy Star window performance ratings vary by region since windows perform differently in different climates. Areas that have Energy Star-rated products are blue on Energy Star maps. The two factors that vary regionally are the U-factor and SHGC.

Below are U-factor and SHGC scores to look for in each climate zone. A window with these scores 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

The northern climate has several recommended ranges. 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 further north you live.

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Factors Affecting Window Energy Efficiency

The factors below influence how successfully your window can insulate.

Frame Materials and Their Impact

Window frame materials can determine how well your window insulates. Consider the options below.

• Aluminum: Durable but less energy-efficient than other types
• Fiberglass: Provides excellent insulation and is durable
• Vinyl: Offers good insulation and is low-maintenance
• Wood: Natural insulator, but requires more maintenance than other types

Glass Types and Energy Performance

A window’s glass type can affect its performance. Read more below.

• Double-pane: More energy-efficient than single-pane windows
• Gas fills: Argon or krypton between panes enhances insulation
• Low-E coatings: Reduce heat transfer and improve insulation
• Triple-pane: Offers the highest level of insulation and energy efficiency

Window Styles and Energy Efficiency

Some window styles are naturally more energy-efficient than others. Read more below.

• Awning windows: As efficient as casement windows
• Casement windows: Reduce air leakage with tight seals
• Double-hung windows: Less efficient because of air leakage points
• Picture windows: Fixed panes that minimize air leakage

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Benefits of Energy Star Certified Windows

Investing in Energy Star-certified windows offers the advantages and benefits below.

Energy Savings and Lower Utility Bills

Energy Star windows can significantly reduce your home’s energy consumption. Up to 30% of a home’s heating and cooling energy goes to counteracting heat loss, according to The Department of Energy. These heating and cooling savings can largely offset the cost of energy-efficient windows.

Improved Home Comfort

Energy-efficient windows can help you to maintain a consistent indoor temperature. This can lead to a more comfortable space, and less of a need for heaters or air conditioning.

Environmental Impact

Energy Star windows help decrease greenhouse gas emissions and your home’s carbon footprint by reducing energy consumption.

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Choosing the Most Energy-Efficient Windows for Your Home

Consider the factors below when you’re selecting your home’s energy-efficient windows:

Assessing Your Climate Zone

Identify your climate zone, and choose windows that are optimal for your local weather conditions.

Considering Your Home’s Orientation

The direction in which your windows face determines how successfully they perform. You might consider a lower SHGC for south-facing windows to reduce heat gain, and look for a low U-factor for north-facing windows to achieve better insulation.

Balancing Energy Efficiency with Other Factors

Consider the additional variables below when deciding which windows are best for your household:

• Budget: Energy-efficient windows are more expensive at first but offer long-term savings.
• Durability: Consider how durable a window is, and how much maintenance it requires.
• Functionality: Make sure you can easily access your windows, and that they ventilate successfully.
• Visuals: Choose windows that complement your home’s style.

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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 which ratings are optimal for your zone.

What does Energy Star-rated window mean?

An Energy Star rating label means the EPA and the Department of Energy have tested and certified the window for its performance.

Are Energy Star windows worth it?

Yes, Energy Star windows are worth it. 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. Read our complete review of Renewal by Andersen for more information.

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