Fogged windows are caused by a seal failure. The seal that we are speaking of is located around the perimeter of a glass section. Adhesives are used to hold the two pieces of glass to a spacer bar, the material that separates the two pieces around the perimeter of the glass. When a seal failure occurs the adhesives have failed and the glass becomes detached from the spacer bar. During the day the air inside the glass section expands and is pushed out from inside the glass section. During the night the air contracts pulling new air back into the glass section. This new air contains water vapor that can not get out and condenses on the interior surfaces of the glass section. The results are stains and a foggy look that is very unattractive. These failed glass sections can be replaced with new glass sections or you can elect to replace the entire window with a new window made from the material of your choice.