The glass you choose affects a window's price and performance:
In cold climates and hot ones, single-pane windows are best reserved for garages and other spaces that don't require heating or cooling. However, single-panes may be adequate in areas with brief heating and air-conditioning seasons.
Most new homes have this type. It consists of two sealed panes, usually separated by an aluminum spacer that includes a desiccant to keep moisture from condensing between the panes. Once moisture does condense between the panes, the only way to get rid of it is to replace the glass.
In a regular double-glazed window, air fills the gap between the panes. A step up in thermal performance and price are windows filled with an inert gas, usually argon. Argon-filled glazing achieves its optimum performance with a half-inch space between panes. Air-filled windows perform best with a space of one-half to one inch.
Low-e, shorthand for low-emissivity, refers to a coating that alters the way the glass transmits visible and invisible light. Much of the sun's radiant energy passes through ordinary glass and warms the objects in a room. In the winter, a warm room re-radiates energy back through the window to the outdoors as long-wave infrared radiation. Some experts say that such long-wave infrared accounts for as much as 60 percent of the heat lost through a window. A low-e coating helps reduce heat loss in the winter and heat gain in the summer by blocking nearly all the long-wave infrared. Some low-e coatings, designed for hot climates or southern exposures, reduce the buildup of heat from the sun. Other low-e coatings meant for cold climates allow more of the sun's warmth into the house.
Triple-pane windows provide better insulating ability than a plain double-pane, but few manufacturers offer them because they are heavy and costly.
These are used by some window manufacturers and are a variation of the triple-pane. It sandwiches a polyester film between two pieces of glass. The film, which has a low-e coating, provides extra insulation without adding significantly to the double-pane window's weight and thickness.