The U.S. Environmental Protection Agency (EPA) has released the first draft of Version 1.0 for an Energy Star specification for exterior and interior storm windows, which received extensive comments and contributions from glass manufacturers and other industry members.

The specification would apply to low-E storm windows, which first became commercially available in 2009. The EPA is basing the specification’s criteria on emissivity, solar transmittance (Tsol) and air leakage. EPA did not use U-factor and solar heat gain coefficient as these metrics account for the energy performance of frame materials in addition to glazing materials. Emissivity and Tsol are glass-only properties, and EPA believes that these metrics directly distinguish higher-performing, energy-saving low-E products from conventional products.

The following chart shows the proposed certification criteria:

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 will 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.

Glass manufacturers that participated in the stakeholders comment period included AGC, Cardinal, Guardian, NSG Pilkington and PPG (now Vitro). Their contributions can be read here.