Low E is a metal oxide applied to glass that reflects heat back to its source. The “E” refers to emissivity defined as, the measure of the ability of a surface to radiate energy. Adding Low E to glass will assist in heat control and block UV ray penetration.
The window industry introduced Low E in the 1980’s. Since then technology and research have produced excellent products recognized by Energy Star. The U.S. Department of Energy and the Environmental Protection Agency have developed an ENERGY STAR Designation for products meeting certain energy performance criteria.
There are many choices of Low E available to the consumer. Energy Star recommends different performance ratings depending on climate zones (click here to view map). Low E can vary in its ability to insulate glass and block solar heat gain.
Argon & Krypton Gas:
Argon and Krypton are inert noble gases that are colorless, odorless, tasteless, and non-toxic. Argon and Krypton slow heat transfer through glass. Both gases are denser than air thereby creating an insulation layer between layers of glass.
Argon and Krypton are injected between thermo-pane units at the factory and then hermetically sealed to prevent leakage. Due to the nature of glass, minimal dissipation of gas occurs over time. According to the NFRC, IG (insulated glass) systems containing gas filling other than air must be tested and certified in accordance with the IG Certification Program which will establish proof of gas content to an average minimum initial 90% insulating gas fill content and an average minimum of 80% insulating gas fill content following completion of respective IG durability testing.
At higher elevations gas is not available due to the pressure on the glass at altitude. Altitude maximums are left to the discretion of the window manufacture.
Understanding NFRC sticker on windows:
NFRC is the National Fenestration Ratings Council, a government body that rates and regulates the window industry on the same standards. The NFRC mandates three ratings displayed on a sticker of each window. The mandatory ratings include U-Factor, Solar Heat Gain Coefficient, and Visible Light Transmittance. Optional ratings include Air Leakage and Condensation Resistance. Click here to learn more about the NFRC Sticker.
AL measures the heat loss and gain through window components including cracks, mechanisms, frames, etc. AL is an optional rating that a manufacture can opt to measure. Efficient Windows Collaborative recommend AL rating of .30 or less.
CR measures resistance to condensation build up. CR is an optional rating that a manufacture can opt to measure. CR ratings range from 0-100. The higher the number is the more resistant to condensation build up. Click here to learn more about condensation.