One of the advantages of new window installation is improving the energy efficiency of a home. Old, leaky windows may be responsible for up to 40% of the energy loss when trying to heat or cool a home. By getting rid of air leaks and installing new windows with good energy-performance ratings, the cost of maintaining a pleasant interior home temperature during all seasons may be significantly reduced. In fact, the energy savings may offset a substantial portion of the new window installation costs.

Windows conduct heat directly through the glass, by leaks around them, and by radiating heat from the exterior usually from the sun and from inside the house due to the ambient room temperature when compared to the external environment.

Energy Performance Ratings

The U.S. Department of Energy notes that the National Fenestration Rating Council has a voluntary program that conducts tests and certifies windows for their energy performance and then gives them a label under the ENERGY STAR® program. This program rates windows based on a “U” factor, solar heat-gain co-efficiencies, sunlight transmission, and air leakage.

U-Factor Considerations

The U-factor is the rate that the window conducts non-solar heat. The heat conduction of the window that determines the U-factor includes the transmission of non-solar heat through the glass, any spacer material, and the framing. A low U-factor is better than a higher one.

Solar Heat-Gain Co-Efficiency Ratings

The solar heat-gain co-efficiency (SHGC) is a calculation of the amount of solar radiation that passes through a window, either directly or indirectly, which is then released as heat within a home. One benefit of having a low SHGC rating is that it is easier to cool a home because the windows are better at shading during the hot summers. On the other hand, having a high SHGC rating means that the windows are better at transmitting heat during the winter time to help keep a home warmer. Homes benefit from having both types of windows installed with proper alignments for the seasons.

Sunlight Transmission

The glazing on the window glass impacts the sunlight’s visible transmission (VT). Different types of glazing allow sunlight to pass through the glass and blocks out the heat caused by the ultraviolet rays. The efficiency of window glazing to block heat, while at the same time let as much light through as possible, is called the light-to-solar-gain, which is a ratio of the SHGC and the VT.

Air Leakage

Air leakage is tested by using an air pressure test to determine the amount of air that moves around a window. It is measured by the amount of cubic feet per minute of air passing around a window compared with the square footage of the window frame. Low air leakage is obviously preferred over higher amounts. Proper installation of windows is important to minimize air leakage around them.

Contact the experts at Window World Western Chicago serving the metro area for help with making good choices about energy-efficient windows.