One of the most common uses of passive solar heating, south-facing windows, is also used in homes that are not specially designed for energy efficiency. In conventional homes, windows are responsible for about 25% of all heat lost from the home; even though double-pane windows are more expensive, they will save up to 15% on heating and make the home more comfortable both in temperature and noise. Multi-pane windows help the homes efficiency in both heating and cooling. Double-pane windows insulate the home almost twice as well as single-pane and more expensive double-panes have gases trapped between the glass to slow heat transfer through the window. This insulation helps to keep the sun’s heat inside the home during the winter and, if other techniques are used, out during the summer. Newer windows have an “e” rating: low e windows have a coating inside the double pane window that both help to keep heat inside the home for colder climates, or reflect the heat out of the home and still allow light to enter. Low e windows cost 10 to 15% more than normal double pane windows, but the heating or cooling savings add up quickly. “Superwindows” are the most efficient window. According to Lawrence Berkeley National Laboratory (a part of UC Berkeley which researches for the U.S. Dept. of Energy) it “performs better than an insulated wall in winter, since the sunlight that it admits is greater than its heat loss over a 24 hour period.” The windows have two or more layers of film between their panes that make them similar to quadruple-pane windows and they reduce the amount of ultraviolet rays that enter the home and damage interiors. Solar orientation plays a huge role in all forms of passive solar, but in the case of effectiveness of windows, it is a vital component. South-facing walls get the most sun year round and are the most effective use the sun’s light and heat. Southern walls should have at least “7 to 12 percent glass” according to a recent article by Mother Earth News. The other walls, however, should have less than 4% glass in order to keep unwanted heat gain and loss to a minimum.