Improvements such as replacement windows, insulation and sealing, as well as upgrades on heating and cooling systems are eligible for the tax credit. The adoption of energy-saving technologies such as geothermal heat pumps, solar water heating, small wind generators and photovoltaic systems is also eligible.

If you are planning an energy-efficient remodel, this  New York Times interview with Kateri Callahan, president of the Alliance to Save Energy, a nonprofit group that advocated some of these credits, will help answer many of your questions you might have and show you the ways in which you can take advantage of these incentives.