EPA Issues Draft for Most Efficient Criteria

October 23, 2012

The Environmental Protection Agency has released Draft 2 of proposed eligibility requirements for recognition of windows as Most Efficient under the Energy Star Windows, Doors and Skylights program. The new draft takes into consideration comments received in response to earlier draft requirements issued in September, reports Doug Anderson, EPA's project manager for the Energy Star windows program.

Only residential windows are eligible for Most Efficient status, the latest draft states. Doors, skylights, commercial windows and tubular daylighting devices will not be considered. 

Climate Zone U-factorSHGC
Northern ≤ 0.20≥ 0.20
North Central ≤ 0.20≤ 0.40
South-Central ≤ 0.20≤ 0.25
South ≤ 0.20≤ 0.25

Unlike normal Energy Star criteria, requirements for Most Efficient windows include certification to meet the North American Fenestration Standard/Specification (NAFS) with a Performance Grade ≥ 15.  A U-factor of less than or equal to 0.2 is required across the country, while solar heat gain coefficient requirements vary across the four Energy Star climate zones.

According to Anderson, changes from the initial draft Most Efficient Criteria include removal of a Visible Transmittance minimum for all zones. Stakeholders noted that there were better approaches to achieving EPA's goals than setting a minimum VT criterion. Due to variations in National Fenestration Rating Council test sizes across operator types, whole-product VTs do not provide a consistent basis of product comparison, it was also noted.

In place of VT requirements, the second draft adds an SHGC minimum of 0.20 in the Northern Zone. Stakeholders generally supported replacing the VT criterion with a SHGC minimum, Anderson states. The minimum SHGC selected for the Northern Zone also aligns with the minimum SHGC proposed for the Canadian Most Efficient program for windows.

The second draft also includes a reduction of the maximum SHGC levels in the Southern and South-Central Zones. Stakeholders suggested that EPA change the maximum SHGC levels in the Southern and South-Central Zones to match the Energy Star Draft 1 Version 6.0 specification and the 2012 International Energy Conservation Code.

EPA is soliciting comments on the Most Efficient criteria at windows@energystar.gov. Comments must be received by October 29, 2012.

Upon review and approval of product applications received from partners, EPA will add qualifying models to the 2013 Most Efficient product list for windows from January 1, 2013 through December 31, 2013, the draft requirements note. The 2013 Most Efficient designation may be used in association with window products recognized during this period for as long as the model remains on the market.