This table, ENERGY STAR Qualification Criteria for Residential Windows and Skylights, provides the qualification criteria for each ENERGY STAR climate zone. ENERGY STAR criteria use U-factor (measured in British thermal units over hours times square-feet times degrees Fahrenheit) and Solar Heat Gain Coefficient (or SHGC, a fraction of incident solar radiation) ratings. The qualification criteria for windows are as follows: In the Northern Zone, there are prescriptive and equivalent energy performance criteria. The prescriptive criteria require a U-factor of 0.30 or less and any SHGC. With the equivalent energy performance criteria, U-factor can go up to 0.31 provided the window has an SHGC of 0.35 or greater or the U-factor can go up to 0.32 provided the window has an SHGC of 0.40 or greater. All other zones only have prescriptive criteria. In the North-Central Zone, the U-factor requirement is 0.32 or less and the SHGC must be 0.40 or less. The South-Central Zone allows U-factors of 0.35 or below and SHGC ratings of 0.30 or below. Windows qualified in the Southern Zone can have U-factors of 0.60 or less, but the SHGC must be 0.27 or below. The qualification criteria for skylights are prescriptive only and are as follows: In the Northern Zone, skylights must have a U-factor of 0.55 or less and any SHGC. In the North-Central Zone, skylights must have a U-factor of 0.55 or less and an SHGC of 0.40 or less. In the South-Central Zone, skylights must have a U-factor of 0.57 or less and an SHGC of 0.30 or less. In the Southern Zone, skylights must have a U-factor of 0.70 or less and an SHGC of 0.30 or less.

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