PNNL. 2013. DOE Challenge Home Case Study e2 Homes Winter Park, Florida [2-page summary version]. PNNL-SA-93079, prepared by Pacific Northwest National Laboratory for the U.S. Department of Energy Building America Program.
ENERGY STAR Windows
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Scope
ENERGY STAR Windows
Prescriptive Path: Fenestration shall meet or exceed ENERGY STAR requirements
- Select windows, doors, and skylights to meet ENERGY STAR program requirements for windows, doors, and skylights.
- Note that the U-value and the Solar Heat Gain Coefficient (SHGC) for doors apply to the whole door, not just the glazing portion.
Performance Path: Fenestration shall meet or exceed 2009 IECC requirements
- Select windows, doors, and skylights to meet 2009 IECC standards for windows, doors, and skylights, except fenestration utilized as part of a passive solar design.
Notes:
For Prescriptive Path: All windows, doors, and skylights shall meet or exceed ENERGY STAR Program Requirements for Residential Windows, Doors, and Skylights – Version 5.0 as outlined at the ENERGY STAR Website. For Performance Path: All windows, doors, and skylights shall meet or exceed the component U-factor and SHGC requirements specified in the 2009 IECC – Table 402.1.1. If no NFRC rating is noted on the window or in product literature (e.g., for site-built fenestration), select the U-factor and SHGC value from tables 4 and 14, respectively, in 2005 ASHRAE Fundamentals, Chapter 31. Select the highest U-factor and SHGC value among the values listed for the known window characteristics (e.g., frame type, number of panes, glass color, and presence of low-e coating). Note that the U-factor requirement applies to all fenestration while the SHGC only applies to the glazed portion. The following exceptions apply:
- An area-weighted average of fenestration products shall be permitted to satisfy the U-factor requirements;
- An area-weighted average of fenestration products > 50% glazed shall be permitted to satisfy the SHGC requirements;
- 15 square feet of glazed fenestration per dwelling unit shall be exempt from the U-factor and SHGC requirements, and shall be excluded from area-weighted averages calculated using a) and b), above;
- One side-hinged opaque door assembly up to 24 square feet in area shall be exempt from the U-factor requirements and shall be excluded from area-weighted averages calculated using a) and b), above;
- Fenestration utilized as part of a passive solar design shall be exempt from the U-factor and SHGC requirements, and shall be excluded from area-weighted averages calculated using a) and b), above. Exempt windows shall be facing within 45 degrees of true south and directly coupled to thermal storage mass that has a heat capacity > 20 btu/ft3xoF and provided in a ratio of at least 3 square feet per square foot of south facing fenestration. Generally, thermal mass materials will be at least 2 inches thick.
For ENERGY STAR climate-specific window requirements, please click here.
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Description
Specific guidance describing the difference between the performance and prescriptive paths of ENERGY STAR is available in the ENERGY STAR National Program Requirements.
Prescriptive Path
ENERGY STAR estimates that installing ENERGY STAR-rated windows rather than standard windows can save homeowners about 7% to 15% on their utility bills. ENERGY STAR windows typically consist of two or more panes of glass in a fiberglass, vinyl, wood, or combination frame. An odorless, colorless, nontoxic 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 on one or more of the glass surfaces reduce the infrared radiation from a warm pane of glass to a cooler pane, 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 reducing heat transfer through the window.
ENERGY STAR windows are independently performance tested 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 0.25 to 1.25 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 caused by sunlight. SHGC is measured on a scale of 0 to 1; values typically range from 0.25 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 the 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 cf·m/ft².
- Condensation Resistance measures how well the window resists water build-up. Condensation Resistance is scored on a scale from 0 to 100. The higher the condensation resistance factor, the less build-up the window allows.
Figure 1 - All ENERGY STAR-Qualified Windows Display the ENERGY STAR Label. The label will indicate the climate zones for which this product qualifies. The ENERGY STAR label should be located next to the National Fenestration Rating Council (NFRC) label or NFRC information may be included on the ENERGY STAR label. 
ENERGY STAR establishes U-Factor and SHGC criteria for ENERGY STAR windows based on climate using a climate zone map developed by ENERGY STAR. 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.
Figure 2 - ENERGY STAR Climate Zone Map for Windows
Figure 3 - ENERGY STAR Climate-Specific Criteria for Windows and Skylights
How to Purchase and Install ENERGY STAR Windows
- Determine your ENERGY STAR climate zone for ENERGY STAR window criteria. SEE the ENERGY STAR website for a locator tool based on the builder’s county.
- Find a retailer of ENERGY STAR-qualified windows. Click here for help locating a retailer. If ordering from a showroom or building materials supplier, ask for a product that qualifies for ENERGY STAR in your climate zone.
- Check with local utilities and check the ENERGY STAR website for tax exemptions, tax credits, and rebates that may be available for purchasing ENERGY STAR-rated windows.
- 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.
For more instructions on properly installing windows to keep air and moisture out, see Fully Flashed Window and Door Openings.
For instructions on air sealing around window rough openings, see Window and Door Rough Openings.
Performance Path
When the performance path is followed, fenestration must meet or exceed requirements of the 2009 IECC as shown in Table 1.
Table 1. Fenestration Requirements (adapted from the 2009 IECC)
| Climate Zone | Fenestration U-Factor (excluding skylights) | Glazed Fenestration SHGC |
| 1 | 1.2 | 0.30 |
| 2 | 0.65 | 0.30 |
| 3 | 0.50 | 0.30 |
| 4 except Marine | 0.35 | No requirement |
| 5 and Marine 4 | 0.35 | No requirement |
| 6 | 0.35 | No requirement |
| 7 and 8 | 0.35 | No requirement |
How to Install Windows
- Follow manufacturer’s installation instructions when installing windows to avoid voiding the warranty.
- Properly install windows to keep air and moisture out. See Fully Flashed Window and Door Openings.
- Properly air seal around window rough openings. See Window and Door Rough Openings.
Other Considerations
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 gain. Locate south-facing windows under properly sized overhangs or covered porches to minimize heat gain from high summer sun and maximize gain from low winter sun. Locating deciduous shade trees to the south and west will also minimize summer solar gain and maximize winter solar gain. Consider selecting specific windows for different sides of the house (EPA 2013).
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.
Right and Wrong Images
Presentations
None Available
Videos
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CAD Images
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Compliance
ENERGY STAR Version 3, (Rev. 6)
Thermal Enclosure Checklist, High-Performance Fenestration. Fenestration shall meet or exceed ENERGY STAR requirements (Prescriptive Path). All windows, doors, and skylights shall meet or exceed the component U-factor and SHGC requirements specified in the 2009 IECC – Table 402.1.1. If no NFRC rating is noted on the window or in product literature (e.g., for site-built fenestration), select the U-factor and SHGC from Tables 4 and 14, respectively, in 2005 ASHRAE Fundamentals, Chapter 31. Select the highest U-factor and SHGC value among the values listed for the known window characteristics (e.g., frame type, number of panes, glass color, and presence of low-e coating). Note that the U-factor requirement applies to all fenestration while the SHGC only applies to the glazed portion. The following exceptions apply: a. an area-weighted average of fenestration products shall be permitted to satisfy the U-factor requirements; b. an area-weighted average of fenestration products ≥ 50% glazed shall be permitted to satisfy the SHGC requirements; c. 15 square feet of glazed fenestration per dwelling unit shall be exempt from the U-factor and SHGC requirements, and shall be excluded from area-weighted averages calculated using a and b above; d. one side-hinged opaque door assembly up to 24 square feet in area shall be exempt from the U-factor requirements and shall be excluded from area-weighted averages calculated using and b above; e. Fenestration utilized as part of a passive solar design shall be exempt from the U-factor and SHGC requirements, and shall be excluded from area-weighted averages calculated using a and b above. Exempt windows shall be facing within 45 degrees of true South and directly coupled to thermal storage mass that has a heat capacity > 20 btu/ft3x°F and provided in a ration of at least 3 sq. ft. of South facing fenestration. Generally, thermal mass materials will be at least 2 in. thick.
Exhibit 1: Mandatory Requirements. Fenestration shall meet or exceed latest ENERGY STAR requirements.
Table 402.1.1 Insulation and Fenestration Requirements by Component. 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 must meet the requirements of Table 303.1.3(1) – Table 303.1.3(3). 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.*
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.*
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.*
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.*
*Due to copyright restrictions, exact code text is not provided. For specific code text, refer to the applicable code.
Case Studies
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DOE Challenge Home Case Study e2 Homes Winter Park, Florida [2-page summary version]
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DOE Challenge Home Case Study e2 Homes Winter Park, Florida [4-page version]
PNNL. 2013. DOE Challenge Home Case Study e2 Homes Winter Park, Florida [4-page version]. PNNL-SA-93080, prepared by the Pacific Northwest National Laboratory for the U.S. Department of Energy Building America Program.
References
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2009 IECC—International Energy Conservation Code
2009 IECC, International Energy Conservation Code. International Code Council, Washington, D.C.
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2012 IECC—International Energy Conservation Code
2012 IECC, International Energy Conservation Code. International Code Council, Washington, D.C.
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DOE Challenge Home National Program Requirements
DOE. 2012. DOE Challenge Home National Program Requirements (Rev. 02). Office of Energy Efficiency and Renewable Energy, U.S. Department of Energy, Washington, D.C.
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ENERGY STAR Qualified Homes, Version 3 (Rev. 06) Inspection Checklist for National Program Requirements
EPA. 2012. ENERGY STAR Qualified Homes, Version 3 (Rev. 06) Inspection Checklist for National Program Requirements. U.S. Environmental Protection Agency, Washington, D.C.
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Residential Windows, Doors, and Skylights
EPA. 2013. Residential Windows, Doors, and Skylights. U.S. Environmental Protection Agency, Washington, D.C.
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Thermal Enclosure System Rater Checklist Guidebook
EPA. 2011. Thermal Enclosure System Rater Checklist Guidebook. U.S. Environmental Protection Agency, Washington, D.C.
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What Makes Energy Star: Performance Criteria
EPA. 2013. What Makes Energy Star: Performance Criteria. U.S. Environmental Protection Agency, Washington, D.C.
