This is a excellent article posted by the Home Energy Magazine in 2000 from laboratory testing done by the Oak Ridge National Laboratory to determine whether storm windows actually make a significant impact on a homes energy consumption. The findings have clearly shown that, indeed simply properly installing good storm windows makes a significant difference, even if you already have double insulated glass windows.

Putting up storm windows on an older home can do more than simply protect the windows from storm damage, and even more than cut down on conductive heat loss. It can also significantly reduce air infiltration. This fact was recently demonstrated by a team of researchers at Oak Ridge National Laboratory who fitted two single-glazed, double-hung sash windows with storm windows, put the assemblies in a simulated weather chamber, and measured air pressure and temperatures on both sides of each assembly for a period of 30 days. The results showed that air infiltration is indeed reduced with storm window additions.