New Windows Improve Energy Efficiency in Homes and Businesses

Whether selecting windows for new construction or window replacement, it is important to understand the role windows play in improving energy efficiency and reducing energy costs. Windows make up part of a home or businesses’ building envelope. The components making up the shell of your structure or building envelope include window, doors, roofing, walls, and foundations. The building envelope separates the outside world from your interior space and help to regulate temperature, airflow, and moisture control.

In the 1980s, a major shift in window manufacturing took place in building codes requiring vinyl rather than aluminum windows. Although aluminum was more durable, the metal conducted heat and cold, thus compromising the building envelope. In addition, because of its conductive properties, aluminum windows were prone to producing window condensation. Along came the advent of vinyl windows.

Technological advancements over the intervening years resulted in the move from single pane windows to insulated windows also known as double paned windows. In fact, there are even triple-paned windows available today. Argon gas fills the space between most windows, although some windows contain krypton gas between panels, a more costly and much more energy-efficient option. Some windows contain a mix of these gases.

Another factor contributing to higher energy efficiency is the use of metallic coatings applied to one or two of the glass surfaces, depending upon if they are dual or triple glazed windows. The metallic coating is referred to as low emissivity or more commonly as “Low E”. Although tinting of glass is still available, used mostly in warmer regions, the Low “E” coating has high energy efficiency while allowing more visible light to be transmitted. After market tinting – although available – is often discouraged because it voids the window manufacturer warranty for glass breakage due to heat stress cracks.

The National Fenestration Rating Council (NFRC) created a system to help consumers understand the energy measurements of windows through product labeling. Affixed at the time of manufacturing, the labels are required so consumers know exactly what they are purchasing. The NFRC measures the entire performance of the window’s components as a whole, inclusive of the glass and frame. Information contained on each label includes the following:

1. U-Factor: U-factor or rate of heat loss where the lower the number, the greater the window resists heat flow. The U-factor range is typically 0.50 to 0.15, where high efficient double-pane windows have a U-factor of 0.30 and some triple-pane windows achieve U-factors of 0.15.

2. Solar Heat Gain Coefficient (SHGC): The SHGC ranges between 0 and 1, with a lower coefficient indicating less solar heat transmitted through a window. This rating applies to the entire window.

3. Visible Transmittance (VT): The VT captures the amount of visible light transmitted through a window. Most window VT rating falls between 0.30 and 0.70 where the lower the number, the less light transmitted. Higher VT windows maximize daylight and view.

4. Air Leakage (AL): Because window frames contain seams, the potential for air leakage exists from the manufacturing process. The lower the AL level, the less airflow that takes place through these seams. A rating of 0.30 or less is ideal, although this rating is optional on the BFRC label.

5. Condensation Resistance (CR): The CR indicates resistance of condensation on the inside of a window surface. With a range of 1 to 100, a higher CR is better able to resist condensation. This measure is also optional on the NFRC label.