Tuesday, June 30, 2009

SmartSun, StupidLaw

Looking through Home Depot last night, I saw that Andersen is now advertising Low-E4 SmartSun glass as the way to qualify for the 30% federal tax credit on energy efficiency improvements like replacement windows. See, the new IRS rules (as of June 1) require that the Solar Heat Gain Coefficient (SHGC) on windows be 0.30 or less, even though that’s backwards for an area that actually has a winter (such as, say, the entire northern United States). Andersen’s regular Low-E4 glass in the windows we’re planning on has an SHGC of 0.31, so it doesn’t qualify. To get 30% back from the federal government, we have to buy windows designed for use in Arizona.

Andersen touts that the SmartSun glass blocks 95% of UV rays, which sounds much more impressive if you don’t know that their regular Low-E4 glass blocks 84% of UV rays. And the SmartSun glass only transmits 7% less light than the Low-E4 glass, unless you think that going from 72% light transmission to 65% light transmission is more like a 10% reduction. (Aren’t numbers fun?) But the real silliness is that it’s far more energy efficient in the northern US to promote solar heat gain during the relatively long winter heating season, and use deciduous trees to reduce solar heat gain during the relatively short summer cooling season. The Efficient Windows Collaborative shows that choosing windows with a significantly lower SHGC and comparable other specs can raise your total energy bill by 5% or more in Boston. EnergyStar has been scrambling to reconcile their rules with the new tax credit rules, since EnergyStar has had a regional approach to certifying windows that takes into account differences in regional climate.

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