ENERGY STAR Windows

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Climate

If you are building to meet an energy-efficiency program certification, refer to that program’s guidance for climate-specific criteria. Criteria for the DOE Zero Energy Ready Home and ENERGY STAR Certified Homes are provided in the Compliance tab.

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 different window models for different sides of the house to maximize beneficial solar gain and minimize unwanted heat gain (EPA 2013).

IECC Climate Zones

IECC Climate Zone Map

Description

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 (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 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-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. Reference

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 cfm/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.

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 - All 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.  Reference

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. 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 = CZ 1 and 2, the South-Central region = CZ3, the North-Central region = CZ 4, and the Northern region = CZ 5, 6, 7, and 8. Figure 3 shows the ENERGY STAR for Windows, Doors, and Skylights criteria Version 5, which was adopted April 2, 2009, and took effect January 4, 2010.

Note that the current version of ENERGY STAR Program Requirements for Residential Windows, Door, and Skylights is Version 5.0. This version 5.0 is under revision; a Version 6.0 specification was approved and will take effect on January 1, 2015, with the exception of the criteria for windows in the northern climate, which will take effect on January 1, 2016

ENERGY STAR Climate Zone Map for Windows

Figure 3 - ENERGY STAR Climate Zone Map for Windows  Reference

ENERGY STAR Climate-Specific Criteria for Windows and Skylights

Figure 4 - ENERGY STAR Climate-Specific Criteria for Windows and Skylights  Reference

How to Purchase and Install ENERGY STAR Windows

  1. 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.
  2. 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.
  3. 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.
  4. 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.
  5. Properly install windows to keep air and moisture out. See Fully Flashed Window and Door Openings.
  6. Properly air seal around window rough openings. See Window and Door Rough Openings.

How to Meet the Fenestration Requirements of DOE Zero Energy Ready Home

The DOE Zero Energy Ready Home program allows builders to choose either a prescriptive path or performance path. The prescriptive path requires that all labeled homes meet or exceed the latest ENERGY STAR Program Requirements for Residential Windows, Doors, and Skylights in effect at the time of project permitting. Builders using the Zero Energy Ready Home prescriptive path must meet or exceed the criteria listed in Exhibit 2 of the National Program Requirements. Builders using the Zero Energy Ready Home performance path must use these criteria when modeling the target home. See the Compliance tab for specific program details and exceptions.

How to Meet the Fenestration Requirements of ENERGY STAR Certified Homes

Builders, contractors, and home owners wishing to meet the fenestration (window) requirements of ENERGY STAR Certified Homes should see the ENERGY STAR Certified Homes National Program Requirements and Inspection Checklists. The latest version (Ver 3.0, Rev. 07) allows two paths: a prescriptive path and a performance path.

Prescriptive Path

The Prescriptive path requires that windows meet or exceed the ENERGY STAR Program Requirements for Residential Windows, Doors, and Skylights (Version 5.0, 2009), which are shown in Figure 3 above and listed on the ENERGY STAR website. Additional details and exceptions relevant to these criteria are listed under the Compliance tab of this guide.

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, Table 402.1.1)

IECC table

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.

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Scope

Prescriptive path: fenestration shall meet or exceed ENERGY STAR requirements

Select and install high-performance windows, preferably windows that are ENERGY STAR rated or that meet or exceed the ENERGY STAR program requirements for windows, doors, and skylights.

DOE Zero Energy Ready Home Notes:

The U.S. Department of Energy’s Zero Energy Ready Home Program allows builders to choose either a prescriptive path or performance path in order to certify their homes as DOE Zero Energy Ready Homes. The Zero Energy Ready Home National Program Requirements specify as a mandatory requirement (Exhibit 1, #2.1) that all labeled homes, whether prescriptive or performance path, have windows that meet or exceed the latest ENERGY STAR Program Requirements for Residential Windows, Doors, and Skylights, which are in force at the time of project permitting. For homes achieving PHIUS+ certification where triple-glazed window assemblies with thermal breaks/spacers between the panes are used, such windows are deemed to meet this requirement even in the absence of an ENERGY STAR certification.

In Exhibit 2, the DOE Zero Energy Ready Home National Program Requirements specify more stringent fenestration (window) criteria, based on the climate zones defined in the International Energy Conservation Code (IECC 2012):

  • IECC Climate Zone 1 and 2 - SHGC = ≤0.25, U factor= ≤0.4
  • IECC Climate Zones 3 and 4 except Marine – SHGC = ≤0.27, U factor= ≤0.3
  • IECC Climate Zones 5-8 and Marine 4 - SHGC = any, U factor= ≤0.27

Builders using the Zero Energy Ready Home prescriptive path must meet or exceed these criteria. Builders using the Zero Energy Ready Home performance path must use these criteria when modeling the target home. See the Compliance tab [link] for specific program details and exceptions.

ENERGY STAR Notes:

The ENERGY STAR Certified Homes (Ver 3. Rev. 07) National Program Requirements allow builders to choose either a prescriptive path or performance path in order to certify their homes as ENERGY STAR homes. The prescriptive path requires that builders select windows that meet or exceed the ENERGY STAR Program Requirements for Residential Windows, Doors, and Skylights.
Note that the current version of ENERGY STAR Program Requirements for Residential Windows, Door, and Skylights is Version 5.0. This Version 5.0 is under revision; a Version 6.0 specification was approved and will take effect on January 1, 2015, with the exception of the criteria for windows in the northern climate, which will take effect on January 1, 2016.

The performance path requires that fenestration meets or exceeds the U-factor and SHGC requirements specified in the 2009 IECC. See the Compliance tab for specific program details and exceptions.

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Compliance

DOE Zero Energy Ready Home (Rev. 04)

The DOE Zero Energy Ready Home program allows builders to choose either a prescriptive path or a performance path in order to certify their homes as Zero Energy Ready Homes.

The U.S. Department of Energy Zero Energy Ready Home Program’s National Program Requirements (Rev 04) specify as a mandatory requirement (Exhibit 1, #2.1) that all labeled homes shall meet or exceed the latest ENERGY STAR Program Requirements for Residential Windows, Doors, and Skylights in effect at the time of project permitting.

In Exhibit 2 of the Zero Energy Ready Home National Program Requirements, DOE specifies more stringent fenestration (window) criteria. Builders using the Zero Energy Ready Home prescriptive path must meet or exceed these criteria. Builders using the Zero Energy Ready Home performance path must use these criteria when modeling the target home. These fenestration requirements are shown in Figure 1, excerpted from Exhibit 2 of the DOE Zero Energy Ready Home National Program Requirements.

ZERH home compliance table

Relevant Footnotes from Zero Energy Ready Home National Program Requirements

(12) Windows shall meet the ENERGY STAR Window Product Criteria which are in force at the time of the project permitting. Visit the website for current ENERGY STAR Window Product Criteria. For homes achieving PHIUS+ certification where triple-glazed window assemblies with thermal breaks/spacers between the panes are used, such windows are deemed to meet this requirement even in the absence of an ENERGY STAR certification.

(13) Fenestration shall meet the applicable ENERGY STAR Window Product Criteria for U and SHGC, with the following exceptions:

  1. An area-weighted average of fenestration products shall be permitted to satisfy the U-factor requirements;
  2. An area-weighted average of fenestration products ≥ 50% glazed shall be permitted to satisfy the SHGC requirements;
  3. 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;
  4. 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;
  5. 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 / ft3 x °F and provided in a ratio of at least 3 sq. ft. per sq. ft. of south-facing fenestration. Generally, thermal mass materials will be at least 2 in. thick.

(7) State energy code specifications that exceed the DOE Zero Energy Ready Home National Program Requirements always take precedence and shall be used instead of DOE Zero Energy Ready Home specifications to determine DOE Zero Energy Ready Home compliance. In states where the residential provisions of the 2012 International Energy Conservation Code (IECC) have been adopted, the Target Home specifications (Exhibit 2) will be updated to reflect the specifications of the 2015 IECC within 6 months of the 2015 IECC publication date. DOE will maintain a list of state-specific compliance requirements and timelines on the DOE Zero Energy Ready Home website. 

(25) All decorative glass and skylight window areas count toward the total window area to above-grade conditioned floor area (WFA) ratio.

(26) DOE strongly encourages all DOE Zero Energy Ready Home partners to consider using R-5 windows in cold climates in anticipation of them becoming the state-of-the-art window choice in the near future. Visit the DOE web site for more details and sources of these windows.

(27) For homes using Exhibit 2 for Prescriptive compliance with the DOE Zero Energy Ready Home, the exceptions listed in Footnote 11 above apply to the U-Value and SHGC requirements in Exhibit 2.

(28) For Prescriptive Path: All decorative glass and skylight window areas count toward the total window area to above-grade conditioned floor area (WFA) ratio. For homes using the Prescriptive Path that have a WFA ratio > 15%, the following additional requirements apply:

a. In Climate Zones 1, 2, and 3, an improved window SHGC is required and is determined by:
Improved SHGC = [0.15 / WFA] x [ENERGY STAR SHGC]
Where the ENERGY STAR SHGC is the maximum allowable SHGC in Exhibit 1, ENERGY STAR Reference Design, for the Climate Zone where the home will be built.

b.    In Climate Zones 4, 5, 6, 7, and 8, an improved window U-Value is required and is determined by:
Improved U-Value = [0.15 / WFA] x [ENERGY STAR U-Value]
Where the ENERGY STAR U-Value is the maximum allowable U-Value in Exhibit 1, ENERGY STAR Reference Design, for the Climate Zone where the home will be built. 

ENERGY STAR Version 3, (Rev. 07)

The ENERGY STAR Certified Homes (Ver 3. Rev. 07) National Program Requirements allow builders to choose either a prescriptive path or performance path in order to certify their homes as ENERGY STAR homes.

The prescriptive path requires that builders select windows that meet or exceed all of the requirements listed in Exhibit 1: ENERGY STAR Reference Design (See Figure 2). The fenestration requirements in this figure are identical to the ENERGY STAR Program Requirements for Residential Windows, Doors, and Skylights, Version 5.0.

ENERGY STAR Windows

The performance path provides builders the flexibility to select a custom combination of measures for each home that is equivalent in performance to the minimum requirements of the ENERGY STAR Reference Design Home, Exhibit 1. Equivalent performance is assessed through energy modeling using a RESNET-accredited Home Energy Rating software program to determine the Home Energy Rating System index for a target home and meeting that target score.
(13) For Prescriptive Path: All windows, doors, and skylights shall meet or exceed the ENERGY STAR Program Requirements for Residential Windows, Doors, and Skylights – Version 5.0.

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:

  1. An area-weighted average of fenestration products shall be permitted to satisfy the U-factor requirements;
  2. An area-weighted average of fenestration products > 50% glazed shall be permitted to satisfy the SHGC requirements;
  3. 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;
  4. 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;
  5. 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/ft3  x o F 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.

2009 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.*

2009 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 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.*

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.*

*Due to copyright restrictions, exact code text is not provided.  For specific code text, refer to the applicable code.

More Info.

Case Studies

  1. Author(s): PNNL
    Organization(s): PNNL
    Publication Date: January, 2013

    Case study about the first certified DOE Zero Energy Ready Home—the “Wilson Residence” in Winter Park, Florida.

  2. Author(s): PNNL
    Organization(s): PNNL
    Publication Date: September, 2013

    Case study of a DOE Zero Energy Ready Home in west Connecticut that scored HERS 39 without solar PV. The 3,000 ft2 two-story home has R-33 double-walls, R-72 flat roof with closed-cell foam and blown cellulose, an ERV, and LED lighting.

  3. Author(s): PNNL
    Organization(s): PNNL
    Publication Date: January, 2013

    Case study of a DOE Challenge Home in Winter Park FL that scored HERS 57 without PV or HERS -7 with PV. This 4,305 ft2 custom home has autoclaved aerated concrete walls, a sealed attic with R-20 spray foam, and ductless mini-split heat pumps.

  4. Author(s): BA-PIRC
    Organization(s): BA-PIRC
    Publication Date: November, 2013

    Case study describing a package of energy- efficiency measures for new manufactured homes in the Pacific Northwest, including triple-pane highly efficient windows.

References and Resources*

  1. Author(s): DOE
    Organization(s): DOE
    Publication Date: April, 2014

    Standard requirements for DOE's Zero Energy Ready Home national program certification.

  2. Author(s): EPA
    Organization(s): EPA
    Publication Date: June, 2013

    Standard document containing the rater checklists and national program requirements for ENERGY STAR Certified Homes, Version 3 (Rev. 7).

  3. Author(s): EPA
    Organization(s): EPA
    Publication Date: January, 2013

    Information sheet with residential window, door and skylight energy savings and tax credit information for consumers.

  4. Author(s): EPA
    Organization(s): EPA
    Publication Date: October, 2011

    Guide describing details that serve as a visual reference for each of the line items in the Thermal Enclosure System Rater Checklist.

  5. Author(s): EPA
    Organization(s): EPA
    Publication Date: January, 2013

    Information sheet outlining the criteria for ENERGY STAR qualified, windows, doors, and skylights.

Last Updated: 05/09/2014

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