If your budget allows, upgrading windows to better-sealed and better-insulated models can pay huge dividends in the fight against high energy costs [source: Energy Star]. Energy-efficient windows typically use a number of features to separate the climate-controlled air in your home from outside air. Your budget may allow you to install multipane windows, in which the space between panes is filled with an insulating gas, such as argon [source: Efficient Windows Collaborative]. Insulating windows in this manner improves their U-factor, a measure of how well the windows prevent heat from escaping. A lower U-factor number identifies a more efficient window [source: Putnam].
The glass on these efficient windows is often tinted or treated with a glazing material that reduces the solar energy allowed into the home [source: Efficient Windows Collaborative]. This not only reduces glare, but also improves the windows' Solar Heat Gain Coefficient (SHGC), a measure of how the windows prevent sunlight from raising the home's indoor temperature [source: Putnam]. As with U-factor, a lower SHGC value identifies a more efficient window.
Often, multipane and tinting or glazing technologies are combined to produce custom windows that meet the specific insulation needs of a given house. If your budget doesn't leave room for the top end of the efficient window spectrum, something as simple as selecting windows with nonmetallic frames (the metal transmits heat through the wall) can provide some savings at a more reasonable cost [source: Efficient Windows Collaborative].