Aluminum storm windows are your best bet to not only save heat but protect your original windows from the elements. Protecting your window with a storm window also defers window maintenance.
The secret to energy savings is to have storm windows with Low E glass. This is something that the older storm windows do not have.
The secret to a beautiful window is based on how many tracks the storm window has.
Exterior storm windows come in triple track, double track, and single track. Double and single track storms are new to the scene. The reason for these tracks is to store the screen and storm window when not in use.
Triple track storms are the best for storage. This convenience comes at the cost of an ugly storm window, however. Of course this is better than having a replacement window but there are better options.
Old House Guy recommends two options: Double track and Single track storm windows.
Double Track Storm Windows
Double track storms keep the screen in place at the lower sash unless you remove it. The storm window stored in the upper sash slides down when used. The difference is there is one less track to make the screen disappear. This one less track allows this storm window to be much smaller. Where the triple track extends proud of the window casing looking obtrusive, the double track extends outward a small amount. There is a nice shadow line around the perimeter, where the storm window meets the window casing. Quanta Panel manufactures this storm window.
Single Track Storm Windows
Single track storms do not store the window or screen when not in use. The window or screen is easily attached to the frame with clips. When the storm window or screen is not in use it must be stored elsewhere. You may think this is a huge inconvenience but really it is worth the trouble for a beautiful window. This storm window is barely noticeable when on your window. Allied Windows manufacturers this “invisible” storm window.
Allied Windows storm windows are custom windows made for arched and any shape or size window. They also make double-track storm and interior storm windows.