WINDOW PERFORMANCE The Learning Center Any operable window will have some degree of air and water infiltration. The only way to totally eliminate air and water from entering is to completely seal the exterior with caulking, which obviously would make the window inoperable. The trick then is to design a product that you can open and close while minimizing the amount of air and water that passes through it. Test methods used by the industry and by the government to determine water resistance are ASTM E 331 and ASTM E 547. These nationally recognized standards require the simultaneous application of water and pressure to the exterior surface of the window. Water is applied to the exterior surface of the window at a rate of 5 gallons per square foot per hour. This rate corresponds to a rainfall of eight inches of water per hour. According to Technical Paper No. 40 on rainfall frequency published by the National Weather Service, the greatest rainfall anywhere in the contiguous 48 United States for a one hour period during a span of 50 years is less than five inches per hour. Therefore, windows are put through water tests far greater than any rainfall will ever produce. To simulate moving air and wind striking a window, the Water Resistance Test is conducted at a pressure equal to 15% of the design pressure, but is never less than 2.86 PSF (corresponding to a wind velocity of 33.4 MPH). The significance of these pressures becomes apparent when they are related to the height they will raise water. This height is referred to as water head. The higher the pressure, the higher the height of water required to balance it. 3. How is a window tested for water resistance? < back to list of questions about window performance 1-877-SWING CLEAN info@energyswingwindows.com 3245 Miracle Drive Murrysville, PA 15668 724-387-2991 PA Contractor ID PA001856