Two important ratings to check when buying windows and glazed doors are the R-value and the U-value. See Window R-Values and U-Values.

Insulating glazing typically has two, or sometimes as many as three, panes of glass sealed together with either air or argon gas trapped between them to act as an insulator.

Some units have a plastic film suspended between two glass panes. If the unit is properly sealed, condensation shouldn't occur between the panes; sometimes a drying agent (called a desiccant) is used in the spacer (the strip inside the panes that helps keep them apart) as added insurance against condensation.

There is no easy way to get rid of condensation in dual glazing, so one very important reason for buying windows and doors with a strong warranty is to ensure that they will be backed if the seal fails and condensation does occur.

You will discover that there are also a number of glass products on the market for special situations and uses, including safety glass and stained glass. Also see the HomeTips closer look at both high-performance and specialty glazing.

Low-Emissivity Glass
Low-emissivity, or low-e, glazing has a film applied to one of the glass surfaces or suspended between the panes. This coating or film allows light in but also prevents some solar rays from being transmitted through the glass.

A low-e coating can help keep your home cool on a hot day by blocking longer-wave radiant heat from entering, and on a cold day it can prevent the radiant interior heat from escaping through the glass. Low-e coatings also block ultraviolet rays, which reduces the fading of floors, floor coverings, drapes, and upholstery.

See more about Buying Window Glass:

• High-Performance Window Glass
• Safety Glass Windows
• Stained Glass Windows
• Tinted Glass and Reflective Glass
• Window Film
• Window R-Values and U-Values