The swiftest savings come from sealing air leaks in your home’s walls, windows, and especially it’s ductwork, which 33 percent of respondents answered correctly. “Leaky return ducts can also introduce unwanted air pollutants into the home.,” adds Kathleen Hogan, Deputy Assistant Secretary of Energy Efficiency at the Department of Energy. Duct insulating and sealing are best left to a professional and could lower your annual heating and cooling bills by $400.