Energy Star Updates Draft Storm Window Specification

April 16th, 2018 by Trey Barrineau

The Environmental Protection Agency (EPA) held a webinar last week to discuss revisions to a proposed new Energy Star specification for exterior and interior storm windows.

The EPA released the first draft of the specification in July 2017. It would apply to low-E storm windows, which first became commercially available in 2009. The EPA is basing the criteria for the specification on emissivity, solar transmittance (Tsol) and air leakage. It did not use U-factor and solar heat gain coefficient because these metrics include the energy performance of frame materials in addition to glass. 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 second draft of the specification was released earlier this month after EPA made several revisions based on comments from industry stakeholders. One of the big changes involved the labels for storm windows, which have been changed to prevent confusion among consumers.

“This is a pretty decent solution for everybody, and it distinguishes the storm window label from a window label,” said Doug Anderson, the EPA’s manager for the Energy Star storm windows program.

Anderson added that while storm windows with low-e glass would form the core of the new specification, storm doors with low-E glass won’t be eligible for it yet.

“Storm doors might be cost-effective, but we just don’t have the data,” he said.

After reviewing feedback from stakeholders, EPA revised the specification to require an emissivity rating less than or equal to .22 for all climate regions. Solar transmission would vary by region:

The air leakage requirements were unchanged from the first draft specification:

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.

Anderson said EPA added stronger language in the installation about thermal breaks when installing storm windows over metal frame primary windows, as well as  guidance on safe removal and recycling of existing storm windows.

For more information and documents related to the proposed storm window specification, follow this link.

Stakeholders are invited to provide feedback on the Draft 2 specification and supporting analysis documents. Written comments should be submitted to EPA at

by May 4.

EPA hopes to publish the final draft specification in June or July.

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