Purchasing double glazed windows is an investment in the home and brings major improvement to the home's exterior and interior spaces. A window's function is to bring light and air to the inside of the home as well as accentuate the homes design. To accomplish this, manufacturers offer window units in a variety of models and materials such as metal, fiberglass, vinyl and wood. Glass features include square or diamond panes, and detailing such as beveled glass.

Double glazing can reduce heating and cooling bills and promote a more energy efficient home. The control of heat exchange through the windows can regulate temperatures and cut down on drafty areas. Windows with better heat performance ensure that less energy is used per home, which in turn helps to lower carbon dioxide emissions -- a by-product of power plants.

Basic components of a double glazed window are the glazing, frame or sash, and spacer. Two panes of glass are used, one in front of the other, with a small space in between the panes. To help insulate the unit, a layer of air or non-toxic gas is used to fill the space before the window is sealed. The spacer is a desiccant filled bar, which separates the two glass layers and prevents condensation.

The gas argon or krypton is often added to double glazed windows to give more insulation to homes in cold climates. These colorless, odorless, non-toxic gases demonstrate a better thermal performance than an air layer. The manufacturer fills the inner space of the double glazing and then the unit is sealed. The ideal energy efficient measurement is 11-13mm space between the two panes for argon, and 6mm or less for krypton.

Heat conductivity through glass is measured by the U-factor or U-value -- the better energy performance of the window, the lower the U-factor. Double glazing can have greater resistance to heat transfer by applying a low-emissivity (amount of heat emitted from the glass) coating, which is a clear, metallic finish. A low-emissivity (Low-E) coating reduces the amount of heat the glass emits, and there are also Low-E coatings available to limit the amount of heat (low to high solar gain) transmitted by sunlight.

The measurement of how much heat the sun transmits through a window's glass is called the Solar Heat Gain Co-efficient (SHGC). If the home is in a hot, sunny climate, a coating with both low-emissivity (amount of heat emitted from the glass) and low solar gain will block out heat. To maintain a cooler temperature, the low-emissivity (Low-E) coating covers the outside pane of the double glazed window. To retain heat in a cold climate, the Low-E coating would be on the inside pane, and have a high solar gain property to bring more heat into the home through natural sunlight.

Double glazed windows can be treated to screen out harmful rays, protecting furniture, carpeting and wall hangings. Direct sunlight on fabric and wood can cause damage by bleaching or discoloring the material over a period of time. A special coating can be applied to the glass, which blocks out ultraviolet light, preserving the condition of pictures and furnishings.