The U.S. Environmental Protection Agency (EPA) has released the final draft of Version 1.0 of the Energy Star specification for exterior and interior storm windows.

EPA revised the definitions for air leakage, emissivity, and solar transmittance to align with definitions proposed by the Attachments Energy Rating Council (AERC) to ensure that the metrics used to measure storm window energy performance are consistent. The agency conducted additional analysis on homes with east/west and west-dominated orientations in climate zones 4, 5 and 6. EPA found that high solar transmittance (Tsol) products remained cost-effective for homes with east/west and west-dominated orientations.

EPA conducted additional analysis to evaluate the payback period for low-E storm windows over double-pane clear-glass primary windows. EPA found that although the payback was longer for the products over double-pane clear primary windows, the proposed criteria is  still cost-effective for the consumer.

The final specification requires an emissivity rating less than or equal to .22 for all climate regions. Solar transmission would vary by region:


For testing and certification purposes, storm windows must meet National Fenestration Rating Council (NFRC) 301 for emissivity, NFRC 300 for solar transmission and Attachments Energy Rating Council (AERC) 1.2 in accordance with ASTM E283 for air leakage.

According to the EPA, consumers purchase about 8 million storm windows a year, but only about 10 percent of those products currently use low-E glass. The agency believes that an Energy Star specification could raise market share to 50 percent. EPA says an Energy Star label for low-E storm windows could be useful for consumers in lower-income households who might not be able to afford full window replacements. It will also help households in low-rise multifamily units, households working with weatherization programs and homes in historic districts.

Furthermore, the EPA believes that an Energy Star storm window criteria could save up to 1.2 trillion Btu on a national basis at 50 percent market share. Additionally, the products would have payback periods between 2.4 and 8.5 years, a much shorter time frame than full window replacements.

EPA will take stakeholder feedback until July 30, and it expects to publish the specification in August. E-mail comments to

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