Increasing energy costs have created demand for double pane and other insulating windows to cut down on heat loss through the windows. Energy conservation homes of new construction are utilizing these windows to significantly reduce home heating costs.
However, these double pane windows now available for new construction are a costly and inconvenient solution to the problem in homes with existing single pane windows. Until this time the homeowner has been faced with the costly removal and discarding of the window structures of his home and the replacement of them with expensive double pane window assemblies of new construction. Other alternatives have involved the use of blinds or drapes to provide an additional insulating layer. These alternative methods are particularly unsatisfactory for those windows where it is desired to maintain the ability to see through the window. In accordance with the preferred embodiment of the present invention, a border molding strip is placed about the perimeter of an existing window pane. A second pane is then placed upon this border material. A retaining border is then placed to retain the window pane firmly against the border material, thus creating an airtight seal between the existing window pane, the border material and the second window pane. Appropriate adhesive and sealing compounds are applied to insure an airtight seal. Thereafter, the space between the existing window pane and the supplemental pane is purged with dry gas and may be evacuated through an opening exposed under a portion of the retaining means. After the window pane is purged and evacuated, a plug is inserted and the opening in the molding material is closed.