The U.S. Environmental Protection Agency (EPA) announced final criteria for its Energy Star Most Efficient 2024 program this week, including new specifications for windows and sliding glass doors. After a review of the data associated with currently recognized models, officials said they found that updates to the program’s criteria were needed “to recognize the best of Energy Star.” Changes are set to take effect for solar heat gain coefficient (SHGC) requirements in the South-Central zone and the U-factor and SHGC requirements of the Southern zone.

Criteria for skylights will remain unchanged.

While current (2023) criteria calls for SHGC ratings of less than or equal to 0.25 in the South-Central zone, new criteria now calls for equal to or less than 0.23.

The current (2023) criteria calls for a U-factor rating of less than or equal to 0.20 in the Southern zone and SHGC ratings of less than or equal to 0.23. For 2024, two combinations are allowed, including a U-factor of less than or equal to 0.21 and SHGC of less than or equal to 0.23, or a U-factor equal to 0.22 and SHGC less than or equal to 0.21.

The agency is also removing requirements for North American Fenestration Standard/Specification (NAFS) Performance Grades of equal to or greater than 15 for doors, windows and skylights, to help simplify criteria.

Amid a comment period lasting through August 21, 2023, several commenters indicated that changes proposed for the South-Central and Southern zones were “too stringent,” EPA officials said, while one supported the proposal. One set of proposals from commenters suggested decreasing the U-factor stringency for the South Central and Southern zones from U=0.20 or U=0.22, as proposed by the EPA, to U=0.25. Another commenter suggested increasing the U-factor to 0.23 for those same zones. Program officials did not agree, suggesting that any such changes would reduce energy savings for individual homeowners and “change the criteria so that it would not represent the most efficient products in the marketplace.”

Several commenters suggested that the SHGC requirements for the South Central and Southern zones not go below 0.23, with one claiming that such levels may require tinted glass.

EPA officials bucked those comments as well, suggesting that homeowners in the Southern zone would save less energy. In a memo and associated webinar, officials said they conducted analysis and reviewed data from Energy Star Version 7 criteria, showing equivalent energy performance for the proposed levels, adding, “products are available from several companies that can meet the criteria.”

Two commenters suggested removing the minimum SHGC requirement for the Northern zone, “since some triple pane windows could have trouble meeting the minimum SHGC level.”

Officials rejected that suggestion, explaining that, by their measure, window products with very low SHGC levels in the Northern zone save less energy than medium or higher level SHGC products.

Lastly, several commenters also suggested that EPA retain the Performance Grade (PG) requirement for Most Efficient window, patio door and skylight products, claiming that code adoption of the PG rating was not uniform across the country and “the PG rating encourages some minimum level of strength, safety and durability for the public.” EPA officials explained that inclusion of the PG requirement hasn’t “significantly helped the energy efficiency of products and has made product review slow and burdensome.” Removing the requirement reduces the burden on manufacturers, they said, allowing for a much faster review process.

Officials said the program will only highlight products that are currently available for sale in the U.S., while reminding partners that it is critical to keep product availability information with certification bodies current. Partners must provide all information called for by the recognition criteria to their certification body at the time of certification in order to be recognized by the program.

“While it is our intention to begin automatically nominating window products for Most Efficient recognition in 2024, until that time, partners will need to apply for recognition for all products new to Energy Star Most Efficient in order for the agency to verify that a product meets the recognition criteria,” they added.

Certified products meeting the new requirements will be highlighted as Energy Star Most Efficient for 2024 beginning January 1, 2024.