Double paned windows have several key advantages over standard windows. Among these are better insulative properties, noise reduction, and ease of cleaning. They can also protect items in the house from sun damage, and they easily slide open and lock closed with no cranking or lifting necessary.
In a double paned window, two facing glass panels are set in a frame, separated by a small space 0.5 inch to 0.75 inch (12.7 - 19.05 mm) wide. The void might be filled with air or nontoxic gasses like argon, which can improve insulation. Decorative frames might also be installed between the glass panels to give the impression of individual windowpanes.
Decorative inset frames make double paned windows very easy to clean, as the glass is one solid panel. Also, inset frames are protected from the elements, staying as pristine and clean as the day they were installed, no matter how old or how soiled windows become between cleanings. A squeegee can be used to make the windows look brand new.
Windows of this type can also block street noise more efficiently than traditional windows. This is particularly important for buildings or homes built near high traffic areas or grade schools, but it is also nice to slide a window closed when the neighborhood gardeners are at work.
Although all double paned windows were originally considered energy-efficient, advances in technology since the 1980s have created many grades of efficiency. Picking the right windows can mean a significant savings in energy bills, but what's right for one part of the country might not be right for another, depending on the local climate.
For example, framing materials contribute greatly to the insulation properties of windows. In extremely cold climates, the outer frame should ideally be wood, vinyl or fiberglass. Colder climates can also benefit from gas-filled windows. In areas that have warmer weather year round, however, aluminum frames might be used, and air-filled windows are fine.
Another factor in the efficiency of double paned windows are the various glazings or UV coatings. For those in very cold regions, the UV coating should allow as much solar energy though as possible to maximize the sun's warmth and reduce heating bills. In hot regions, however, UV coatings should be at a maximum to keep out solar heat and reduce air conditioning use. High UV coatings also protect floors, rugs, and photographs from sun damage. In regions in which a combination of weather is normal, windows can be designed with a combination of factors to best maximize energy-savings.
In the United States, the Environmental Protection Agency (EPA) and U.S. Department of Energy grant the Energy Star seal to products that meet the most serious energy-savings guidelines.