Energy Star increases the 12 percent Energy Star EnergyStar.gov ENERGY STAR certified 2015 study by D+R International EnergyStar.gov benefits of ENERGY STAR qualified windows save an average of 12% on energy bills 12% on your utility costs per year up to 6,205 pounds of CO2 emissions make sure the windows are Energy Star-rated save effectiveness anywhere between $27 to $465 per year