Single Pane Storm Windows
One option that consumers have that does not involve replacing their old single pane windows is the use of the storm window. Storm windows are placed either on the inside or the outside of an existing window and they can help to increase the energy efficiency, the insulating properties of the window and often times the overall look and aesthetics of the window itself. The major downfall to the storm windows is that they can be difficult if you want to get ventilation into the home during hot summer months.
Exterior storm windows will typically have a two track or a three track option that will allow for easier opening and closing of the storm window so that ventilation is much more convenient. Often times, a storm window is actually a single pane window.