A cold draft is a sure sign of an inefficient window, but gaps or cracks in or around the window are not the only ways that drafts can occur. While a properly fitted and installed window is extremely important, so are the materials that comprise the panes and frames.

Through conduction, heat is transferred through the window itself. In the wintertime, this means the heat generated by your HVAC system is lost directly through cold, inefficient window panes and window frames.

When warm air comes in contact with a cold window pane, it is cooled, and the cold air sinks while more warm air from your home rises to replace it. This creates a cycle of rising warm air and sinking cool air that creates a cold draft in your home.

For better energy efficiency and to preserve heat, energy efficient windows are made of materials that have a higher insulating value. Features include multiple panes of efficient glass that are often given a reflective coating. The space between the panes is then filled with an insulating gas, such as Argon, which also helps to slow and reduce the transmission of indoor heat to the exterior of your home.

Another label to look for is that of the National Fenestration Rating Council. This label will provide information about "whole window" energy factors. As the name implies, a window's entire energy value is expressed in several values, including:

• U-factor, which measures heat loss. Windows with a lower U-factor are ideally suited for cold climates.

• Solar Heat Gain Coefficient, which measures how much heat from sunlight passes through the window. Windows with a low SHGC are better suited to warmer climates.

• Air leakage factor determines the likelihood of drafts occuring. The higher the number, the more likely the window will be drafy.

• The higher a window's Condensation Resistance, the less likely you are to see water condensing within multiple window glazes.

• Visible Light Transmittance is akin to sunglasses; the higher the number, the less visible light that passes through the window.

The energy efficiency of a window is also affected by an invisible protective layer called an e-coating. Argon or krypton gas sealed between each layer further enhances the efficiency of multiple glazed windows. Various configurations of these factors determine the Energy Star rating and thus the most energy efficient window for your home.

Also keep in mind that a window's energy efficiency is also determined by, among other things, your local climate, the orientation of your home, the size and location of the windows, the method you use to heat and cool your home and the degree of shading around the house.

Additional reporting by Angi contributor Charles R. Hooper.

Editor's note: This is an updated version of an article originally posted on April 17, 2013.

Have you recently installed replacement windows and noticed a difference in energy savings? Tell us about it in the comments section below.