I have a 1940's Cape Cod that I am going to start replacing the original windows wich are about as energy efficient as a screen door, but I atleast have storms on there so I wasn't in the worst possible scenario. Anywho, If I am now gonna have new double or tripple insulated windows, do I even want to keep the storm windows that are on there now ? The ease of taking the strom windows off and putting them back in is no concern. I just want to know if I will really get any added benefit with them there. They do seal quite well, so well infact that I can open the window with the storm closed and feel almost no draft. One person I talked to mentioned I might be creating a "greenhouse" effect causing excess heat between the storm window and the double insulated window.
I have them on my house as original 1959 equipment, and am glad that I do. If nothing else, they keep the majority of the rain off the windows themselves, and minimize the chances of infiltration and leaks. They make a good place for spiders and bugs to go to die, which gets old, but otherwise I'm glad I have them.