In December, Congress reduced the federal tax credit for energy-efficient windows, doors, and skylights for 2011 and changed the qualifying criteria. The Window and Door Manufacturers Association (WDMA) provides an overview [1] of four important changes reflected in the “Tax Relief, Unemployment Insurance Reauthorization and Job Creation Act.”
Qualifying products — All Energy Star-qualified windows, skylights, and exterior doors are eligible. Products must be installed in a consumer's existing primary residence; new construction is not eligible.
Credit amount — Consumers can claim a credit of 10 percent up to $200 of the purchase price of qualifying windows and skylights and 10 percent up to $500 for qualifying exterior doors. Installation costs are not included.
Lifetime cap — There is now a lifetime limit of $500 ($200 for windows/skylights) in total credits that a homeowner can claim from Jan 1, 2006 to Dec. 31, 2011. It is not on top of the $1,500 limit in 2009-2010. So if they have already reached or exceeded the $500 limit, they are no longer eligible to claim the credit in 2011. The $500 aggregate lifetime limit is for any combination of all tax credit qualifying products (HVAC, insulation, roofing, etc), not just windows, doors and skylights. If they have claimed less than $500, they can claim the difference up to the $200 cap for windows and skylights and $500 for exterior doors.
Duration — The revised tax credit is in effect for products installed in a consumer's primary residence between January 1 and December 31, 2011.
Links:
[1] http://archive.constantcontact.com/fs089/1102482301929/archive/1104158009009.html