We are replacing the old windows in this house. The old windows have a single pane glazed sash that lets in the cold weather. The new windows have a double pane glass with a vinyl grid on the outside and a wood grid on the inside. They are a Low-E design that keeps the cold out and the heat in. The old windows have condensation on the inside early in the mornings. The new windows do not. There will be huge energy savings with the new windows.