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High-Performance (ENERGY STAR) Windows

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    Scope Images
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    ENERGY STAR-qualified windows display the ENERGY STAR label
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    Select and install high-performance windows:

    • At a minimum, install windows that are ENERGY STAR rated or that meet or exceed the ENERGY STAR program requirements for windows, doors, and skylights.
    • Consider triple-pane and/or ENERGY STAR “Most Efficient” windows.

    See the Compliance Tab for related codes and standards requirements, and criteria to meet national programs such as DOE’s Zero Energy Ready Home programENERGY STAR Single-Family New Homes, and Indoor airPLUS.

    Description
    Description

    ENERGY STAR estimates that installing ENERGY STAR-rated windows rather than standard windows can save homeowners about 6% to 13% on their utility bills while improving thermal comfort. More than 85% of windows sold in the United States today are ENERGY STAR certified. ENERGY STAR windows typically consist of two or three panes of glass in a fiberglass, vinyl, wood, or combination frame (Figure 1). An odorless, colorless, nontoxic inert gas such as argon or krypton fills the space between the panes to provide better insulation than just air. Special low-emissivity (low-e) coatings (a nearly invisible layer of silver) on one or more of the glass surfaces reflect back infrared radiation, thereby making the window more energy efficient (lowering the U-factor). These coatings also reflect ultraviolet (UV) rays to minimize fading of furniture and drapes. A spacer keeps the panes of glass the right distance apart; some spacers are made of non-metal insulating materials that also insulate the edges of the glass panes further reducing heat transfer through the window.

     

    ENERGY STAR-rated windows.
    Figure 1. High-performance windows like ENERGY STAR-rated windows have features like dual or triple panes, insulated frames, and low-e coatings to improve their efficiency (Source: ENERGY STAR 2021).

     

    ENERGY STAR window criteria are set by the U.S. Environmental Protection Agency (EPA) based on properties that are independently verified according to procedures established by the National Fenestration Rating Council (NFRC). The NFRC label shows performance ratings in five categories.

    • U-Factor measures the rate of heat transfer and tells you how well the window insulates. U-factor values generally range from 0.15 to 1.1 and are measured in Btu/h•ft²•°F. The lower the U-factor, the better the window insulates.
    • Solar Heat Gain Coefficient (SHGC) measures the fraction of solar energy transmitted and tells you how well the product blocks heat from incident sunlight. SHGC is measured on a scale of 0 to 1; values typically range from 0.15 to 0.80. The lower the SHGC, the less solar heat the window transmits.
    • Visible Transmittance (VT) measures the amount of light the window lets through. VT is measured on a scale of 0 to 1; values generally range from 0.20 to 0.80. The higher the VT, the more light you see.
    • Air Leakage (AL) measures the rate at which air passes through joints in a closed window. AL is measured in cubic feet of air passing through one square foot of window area per minute. The lower the AL value, the less air leaks through the window. Most industry standards and building codes require an AL of 0.3 cfm/ft² or less.
    • Condensation Resistance measures how well the window resists water build-up on the inner surface of the window. This could result in mold on the window surface. Condensation Resistance is scored on a scale from 0 to 100. The higher the condensation resistance factor, the less build-up the window allows.

    The NFRC label is combined with the ENERGY STAR label, which shows the U.S. regions where the labeled window meets ENERGY STAR specifications (Figure 2).

     

    All ENERGY STAR-Qualified Windows Display the ENERGY STAR Label.
    Figure 2. ENERGY STAR-qualified windows display the ENERGY STAR label, showing the climate zones for which this product qualifies and the National Fenestration Rating Council (NFRC) ratings (Source: EPA 2014).

     

    ENERGY STAR establishes U-Factor and SHGC criteria for ENERGY STAR windows based on climate using a climate zone map with four zones (see Figure 3). The criteria show the highest U-factor permissible in each climate zone and the SHGC criteria in each climate zone, with higher SHGCs in colder climates and lower SHGCs in hotter climates. The climate zones shown on this map equate to the climate zones shown in the International Energy Conservation Code (IECC) map, as follows:

    • the Southern region = IECC CZ 1 and 2
    • the South-Central region = IECC CZ 3
    • the North-Central region = IECC CZ 4
    • the Northern region = IECC CZ 5, 6, 7, and 8.

     

    ENERGY STAR Climate Zone Map for Windows.
    Figure 3. ENERGY STAR Climate Zone Map for Windows (Source: EPA 2021).

     

    Figure 4 shows the ENERGY STAR Program Requirements for Residential Windows and Skylights, Version 7.0. This version took effect on October 23, 2023. Note that in the northern climate zone there are potential tradeoffs between the U and SHGC values.

     

    ENERGY STAR Climate-Specific Criteria for Windows and Skylights.
    Figure 4. ENERGY STAR Climate-Specific Criteria for Windows and Skylights, Version 6.0 (Source: EPA 2021).

     

    Figure 4. ENERGY STAR Climate-Specific Criteria for Windows and Skylights, Version 6.0 (Source: EPA 2021).

    ENERGY STAR also has a “Most Efficient” program for most of its residential products, including windows. The Most Efficient window criteria requires a U ≤ 0.20, exceeding the performance of the products in any of the four climate zones. These window products are all triple glazed and may be less commonly available, but EPA maintains a web site to search for manufacturers and product lines that meet the Most Efficient criteria.

    Financial Incentives

    Rebate Incentives

    Rebates for windows, skylights, and doors may be available through your local utility company. Check the web site of your local utility and visit the ENERGY STAR Rebate Finder and enter your zip code to see what incentives are available in your area. You can also check with your contractor to see if they know of incentives or rebates in your area.

    Federal Tax Credits

    There are currently federal tax credits for the cost of purchasing ENERGY STAR windows, and skylights for 30% of the cost up to $600. Exterior windows or skylights must meet the ENERGY STAR Most Efficient criteria. This tax credit is available through December 31, 2032. Learn more about this tax credit.

    Assistance for Low-to-Moderate Income Families

    The Department of Energy (DOE) offers a Weatherization Assistance Program (WAP) available for households with lower incomes that qualify for Supplemental Security Income, Aid to Families with Dependent Children, and other income eligibility criteria. This program includes a home energy assessment and common home improvements such as repairing windows or replacing a few damaged windows – but generally do not replace a whole house full of windows. Some programs also offer storm windows. You can also contact your local electric utility to see if they offer energy efficiency home upgrades for low-income customers.

    Modern Storm Windows

    ENERGY STAR certified storm windows are an affordable option for homes where full window replacement may be difficult, such as lower-income households, low-rise multi-family households, households working with HUD or weatherization programs, or households in historic preservation districts.

    ENERGY STAR certified storm windows use “low emissivity” or low-e glass to improve the energy performance of your home compared to clear glass storm windows. ENERGY STAR certified storm windows are designed to allow the right amount of solar heat through your windows to keep your home cool in the summer and warm in the winter, and help you save on energy bills.

    How much can I save with ENERGY STAR Storm Windows?

    EPA estimates that on a national average, ENERGY STAR certified (low-e) storm windows can save homeowners about 20% on their annual heating and cooling bills when installed over single-pane clear glass windows (without existing storm windows). You can expect to pay back the incremental cost of the ENERGY STAR certified storm windows in about three (3) years.

    Additional Benefits of Modern Storm Windows:

    • Can be installed on the interior or exterior of an existing window.
    • Cost ½ to ¼ the amount of common replacement windows with much lower cost installation. They can also be Do-It-Yourself installed without training in a few minutes to save even more money.
    • Come in both fixed and operable (open and close) options and with insect screens.
    • Come in a variety of colors to match your home.
    • Can be purchased conveniently at many home improvement stores and can be specialty manufactured to perfectly fit to your current windows.
    • External storm windows are designed with weep holes to manage moisture while also controlling air leakage.
    • ENERGY STAR certified storm windows have high-gain low-e coatings for Northern climates to optimize solar gain when it is cold. ENERGY STAR storm windows for Southern climates are designed to block solar gain because they are low-gain, low-e, which helps to lower air conditioning costs.

    How to Purchase and Install ENERGY STAR Windows

    1. Determine your ENERGY STAR climate zone for the ENERGY STAR window criteria using the ENERGY STAR climate zone finder tool, which bases the climate zone on the county in which the home is located.
    2. Look for ENERGY STAR-labeled products that meet or exceed the criteria for your climate zone. If ordering from a showroom or building materials supplier, ask for a product that meets the ENERGY STAR criteria in your climate zone. In colder climates, explore the opportunity to go beyond the traditional ENERGY STAR products by specifying Most Efficient products.
    3. If you are seeking to have your home certified under either the DOE Zero Energy Ready Home program or the ENERGY STAR Single-Family New Homes program, see the Compliance tab for additional window specifications to meet those program criteria.
    4. Check with local utilities and check the ENERGY STAR website for information about the federal tax credit for ENERGY STAR-rated windows or for other utility rebate programs. For example, in some parts of the country utilities offer substantial rebates for selecting Most Efficient products. Also see the DOE Database of State Incentives for Renewables & Efficiency for information on additional state, federal, and local tax credits and exemptions.
    5. Follow the manufacturer’s installation instructions when installing the windows to avoid voiding the warranty. Some warranties require that you use an installer certified by the manufacturer.
    6. Properly install windows to keep air and moisture out. See the guide  Fully Flashed Window and Door Openings.
    7. Properly air seal around window rough openings. See the guide Air Sealing Window and Door Rough Openings.
    Success
    Ensuring Success

    Look for or request ENERGY STAR-qualifying products when purchasing windows and follow ENERGY STAR criteria to purchase windows appropriate for the climate zone where they will be installed.

    Push the envelope by selecting ENERGY STAR Most Efficient products where heating loads dominate. Consider, and design for, triple pane windows, or consider thin triple-pane windows.

    Climate
    Climate

    If you are building to meet an energy-efficiency program certification, refer to that program’s guidance for climate-specific criteria. 

    To maximize beneficial solar heat gain and minimize unwanted solar heat gain, consider window location and sizing when designing the house. Limit the number of west-facing windows, especially in hot climates, to limit late afternoon glare and solar heat, unless the windows can be properly shaded. This might be through the use of interior or exterior operable shading, including blinds, shades, or solar screens, which may be fixed or manually or electronically operated. Locate south-facing windows under properly sized overhangs or install fixed or removable awnings or pergolas to minimize heat gain from high summer sun and maximize gain from low winter sun. Locating deciduous rather than evergreen shade trees to the south, east, and west will also minimize summer solar gain and allow winter solar gain. Consider selecting different window properties for different sides of the house to maximize beneficial solar gain and minimize unwanted heat gain. Consider how the occupants might use interior or exterior operable shading in conjunction with windows.

    In cold climates, consider triple-pane windows both for their energy efficiency and for their ability to minimize condensation on window interiors.

    The map in Figure 1 shows the climate zones for states that have adopted energy codes equivalent to the International Energy Conservation Code (IECC) 2009, 12, 15, and 18. The map in Figure 2 shows the climate zones for states that have adopted energy codes equivalent to the IECC 2021. Climate zone-specific requirements specified in the IECC are shown in the Compliance Tab of this guide. 

     

    Figure 1. Climate Zone Map from IECC 2009, 12, 15, and 18.
    Figure 1. Climate Zone Map from IECC 2009, 12, 15, and 18. (Source: 2012 IECC)

     

    Climate Zone Map from IECC 2021.
    Figure 2. Climate Zone Map from IECC 2021. (Source: 2021 IECC)

     

    Training
    Right and Wrong Images
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    Wrong – Window does not meet ENERGY STAR requirements
    Wrong – Window does not meet ENERGY STAR requirements
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    Right – Window meets ENERGY STAR requirements
    Right – Window meets ENERGY STAR requirements
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    Choose high-performance ENERGY STAR-rated windows.
    Choose high-performance ENERGY STAR-rated windows.
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    This home bears a DOE Zero Energy Ready Home label on its front window next to the ENERGY STAR window label.
    This home bears a DOE Zero Energy Ready Home label on its front window next to the ENERGY STAR window label.
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    Version 3.1: Exhibit 1 ENERGY STAR Reference Design Home - Windows (Revision 9)
    Version 3.1: Exhibit 1 ENERGY STAR Reference Design Home - Windows (Revision 9)
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    The windows are ENERGY STAR-qualified double-pane, argon-filled, vinyl-framed windows with a U value of 0.28 and a SHGC of 0.41.
    The windows are ENERGY STAR-qualified double-pane, argon-filled, vinyl-framed windows with a U value of 0.28 and a SHGC of 0.41.
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    Right – A metal flashing was installed behind the first row of siding above the windows to guide water over the trim.
    Right – A metal flashing was installed behind the first row of siding above the windows to guide water over the trim.
    Videos
    Compliance

    Compliance

    The Compliance tab contains both program and code information. Code language is excerpted and summarized below. For exact code language, refer to the applicable code, which may require purchase from the publisher. While we continually update our database, links may have changed since posting. Please contact our webmaster if you find broken links.

    ENERGY STAR Single-Family New Homes, Version 3/3.1

    The ENERGY STAR Reference Design Home is the set of efficiency features modeled to determine the ENERGY STAR ERI Target for each home pursuing certification. The requirements for the Reference Design Home, including the fenestration (windows) requirements, are listed in Exhibit 1 of the National Program Requirements document. They are not mandatory but can be traded off with other measures to achieve the ENERGY STAR ERI Target.

     

    DOE Zero Energy Ready Home (Revision 07)

    Exhibit 1 Mandatory Requirements.
    Exhibit 1, Item 2) Fenestration shall meet or exceed ENERGY STAR window requirements.

     

    2009-2021 IECC and IRC Window U-Factor Requirements Table

    The maximum U-Factor and Solar Heat Gain Coefficient (SHGC) requirements for fenestration (windows) and skylights in new homes, as listed in the 2009, 2012, 2015, 2018, and 2021 IECC and IRC, can be found in this table.

    2009 International Energy Conservation Code (IECC)

    Section 303.1.3 Fenestration product rating: U-factors of fenestration products (windows, doors, and skylights) are determined per NFRC 100 and labeled and certified by the manufacturer. The SHGC must be determined per NFRC 200 and labeled and certified by the manufacturer.  Products with no labels will be assigned a default U factor as listed in Table 303.1.3(1) and a default SHGC value as listed in Table 303.1.3(3).

    Table 402.1.1 lists insulation and fenestration requirements by building component.

    Section 402.3.1 U-factor:  an area-weighted average is allowed to satisfy the U-factor requirements. Section 402.3.2 Glazed fenestration SHGC: an area-weighted average of products with more than 50 percent glazing is allowed to satisfy the SHGC requirements. Section 402.3.3 Glazed fenestration exemption: up to 15 square feet per dwelling unit may be exempted from U-factor and SHGC requirements under the prescriptive approach.  Section 402.3.4 Opaque door exemption: one side-hinged door up to 24 square feet may be exempted from the U-factor requirement.

    2012 IECC

    Section R303.1.3 Fenestration product rating: U-factors of fenestration products (windows, doors and skylights) are determined per NFRC 100 and labeled and certified by the manufacturer. The SHGC and visible transmittance must be determined per NFRC 200 and labeled and certified by the manufacturer.  Products with no labels must meet the requirements of Table R303.1.3(1) – Table R303.1.3(3). Section R402.3.1 U-factor:  an area-weighted average is allowed to satisfy the U-factor requirements. Section R402.3.2 Glazed fenestration SHGC: an area-weighted average of products with more than 50 percent glazing is allowed to satisfy the SHGC requirements. Section R402.3.3 Glazed fenestration exemption: up to 15 square feet per dwelling unit may be exempted from U-factor and SHGC requirements under the prescriptive approach.  Section R402.3.4 Opaque door exemption: one side-hinged door up to 24 square feet may be exempted from the U-factor requirement.

    2015 and 2018 IECC

    Section R303.1.3 Fenestration product rating: U-factors of fenestration products (windows, doors, and skylights) are determined by an accredited independent laboratory per NFRC 100  (except for garage doors whose U factors can be determined in accordance with either NFRC 100 or ANSI/DASMA 105.) They are labeled and certified by the manufacturer. The SHGC and visible transmittance are determined by an accredited independent laboratory per NFRC 200 and labeled and certified by the manufacturer.  Products with no labeled U-factor must meet the requirements of Table R303.1.3(1) or Table R303.1.3(2). Products with no labeled SHGC must meet the requirements of Table R303.1.3(3). 

    Table R402.1.2 specifies Fenestration U-factors and SHGC values by climate zone.  Section R402.3.1 U-factor:  an area-weighted average is allowed to satisfy the U-factor requirements. Section R402.3.2 Glazed fenestration SHGC: an area-weighted average of products with more than 50 percent glazing is allowed to satisfy the SHGC requirements. Section R402.3.3 Glazed fenestration exemption: up to 15 square feet per dwelling unit may be exempted from U-factor and SHGC requirements under the prescriptive approach.  Section R402.3.4 Opaque door exemption: one side-hinged door up to 24 square feet may be exempted from the U-factor requirement.

    Retrofit:  2009201220152018,  and 2021 IECC

    Section R101.4.3 (in 2009 and 2012). Additions, alterations, renovations, or repairs shall conform to the provisions of this code, without requiring the unaltered portions of the existing building to comply with this code. (See code for additional requirements and exceptions.)

    Chapter 5 (in 2015, 2018, 2020). The provisions of this chapter shall control the alteration, repair, addition, and change of occupancy of existing buildings and structures.

     

    2009 International Residential Code (IRC)

    Table N1102.1.1 Insulation and Fenestration Requirements by Component. Section N1101.5 Fenestration product rating: U-factors of fenestration products (windows, Doors, and skylights) are determined per NFRC 100 and labeled and certified by the manufacturer. The SHGC must be determined per NFRC 200 and labeled and certified by the manufacturer.  Products with no labels must meet the requirements of Table N1101.5(1) – Table N1101.5(3). Section N1102.3.1 U-factor:  an area-weighted average is allowed to satisfy the U-factor requirements. Section N1102.3.2 Glazed fenestration SHGC: an area-weighted average of products with more than 50 percent glazing is allowed to satisfy the SHGC requirements. Section N1102.3.3 Glazed fenestration exemption: up to 15 square feet per dwelling unit may be exempted from U-factor and SHGC requirements under the prescriptive approach.  Section N1102.3.4 Opaque door exemption: one side-hinged door up to 24 square feet may be exempted from the U-factor requirement.

    2012 IRC

    Section N1101.12.3 Fenestration product rating: U-factors of fenestration products (windows, Doors, and skylights) are determined per NFRC 100 and labeled and certified by the manufacturer. The SHGC and visible transmittance must be determined per NFRC 200 and labeled and certified by the manufacturer.  Products with no labels must meet the requirements of Table N1101.12.3(1)-N1101.12.3(3). Section N1102.3.1 U-factor:  an area-weighted average is allowed to satisfy the U-factor requirements. Section N1102.3.2 Glazed fenestration SHGC: an area-weighted average of products with more than 50 percent glazing is allowed to satisfy the SHGC requirements. Section N1102.3.3 Glazed fenestration exemption: up to 15 square feet per dwelling unit may be exempted from U-factor and SHGC requirements under the prescriptive approach.  Section N1102.3.4 Opaque door exemption: one side-hinged door up to 24 square feet may be exempted from the U-factor requirement.

    2015 and 2018 IRC

    Section N1101.10.3 Fenestration product rating: U-factors of fenestration products (windows, Doors, and skylights) are determined by an accredited independent laboratory per NFRC 100 and labeled and certified by the manufacturer. The SHGC and visible transmittance are determined by an accredited independent laboratory per NFRC 200 and labeled and certified by the manufacturer.  Products with no labels must meet the requirements of Table N1101.12.3(1)-N1101.12.3(3). 

    Section N1102.1.2 (R402.1.2) Insulation and fenestration criteria are listed in Table N1102.1.2 by climate zone.  Section N1102.3.1 U-factor: an area-weighted average is allowed to satisfy the U-factor requirements. Section N1102.3.2 Glazed fenestration SHGC: an area-weighted average of products with more than 50 percent glazing is allowed to satisfy the SHGC requirements. Section N1102.3.3 Glazed fenestration exemption: up to 15 square feet per dwelling unit may be exempted from U-factor and SHGC requirements under the prescriptive approach.  Section N1102.3.4 Opaque door exemption: one side-hinged door up to 24 square feet may be exempted from the U-factor requirement.

    Retrofit:  2009201220152018,  and 2021 IRC

    Section R102.7.1 Additions, alterations, or repairs. Additions, alterations, renovations, or repairs shall conform to the provisions of this code, without requiring the unaltered portions of the existing building to comply with the requirements of this code, unless otherwise stated. (See code for additional requirements and exceptions.)

    Appendix J regulates the repair, renovation, alteration, and reconstruction of existing buildings and is intended to encourage their continued safe use.

    Retrofit
    Existing Homes

    Choose ENERGY STAR or ENERGY STAR Most Efficient labeled products when replacing windows.

    More

    More Info.

    Access to some references may require purchase from the publisher. While we continually update our database, links may have changed since posting. Please contact our webmaster if you find broken links.

    References and Resources*
    Author(s)
    U.S. Environmental Protection Agency
    Organization(s)
    EPA
    Publication Date
    Description
    Information sheet outlining the criteria for ENERGY STAR qualified, windows, doors, and skylights.
    Author(s)
    Fenestration Manufacturers Association,
    American Architectural Manufacturers Association,
    Window & Door Manufacturers Association
    Organization(s)
    FMA,
    AAMA,
    WDMA
    Publication Date
    Description
    Guide describing the installation of windows in walls that have foam plastic insulating; guide provides several methods for attaching, supporting, and flashing windows in walls with rigid foam sheathing. (Note: The link only goes to the table of contents for the guide, the full guide can be...
    *For non-dated media, such as websites, the date listed is the date accessed.
    Contributors to this Guide

    The following authors and organizations contributed to the content in this Guide.

    Sales
    Building Science Measures
    Building Science-to-Sales Translator

    High-R Window = High-Efficiency Window

    Image(s)
    Technical Description

    There are two levels of window efficiency relative to standard windows: high-efficiency (e.g., ENERGY STAR Certified windows), which perform at least 15% better than standard windows, and ultra-efficient (e.g., most triple-glazed windows) which perform at least 50% better. These windows use a combination of features to reduce heat loss or gain including two or three glass panes separated by insulating spacers, nontoxic gas (e.g., argon or krypton) in the spaces between the glass panes for better thermal resistance, a nearly invisible low-emissivity coating on the glass that keeps heat in during the winter and out in the summer. They also block damaging ultraviolet sunlight (e.g., fading curtains and furniture), and insulate frames.

    High-Efficiency Window
    Sales Message

    High-efficiency windows effectively block unwanted heat gain in summer while retaining your home’s heat in winter. What this means to you is less wasted energy along with enhanced comfort and noise reduction. Wouldn’t you agree high-efficiency windows should be included in every new home?

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