REPLACEMENT WINDOWS The Learning Center Any operable window or door, even new ones, will have some degree of air infiltration. All windows are tested under the influence of a 25 MPH wind, under which the air infiltration rate must be less than 0.30 cubic feet of air per minute, per square foot of window area. Therefore, a 3 feet by 4 feet window can have a total air infiltration of 3.6 CFM. During a 50 MPH wind, the wind pressure is four times greater than it is at 25 MPH. As a result, considerably more leakage will occur at higher wind speeds. Most new windows will have an air infiltration rate below the 0.30 maximum. However, a number of factors such as window size, location, building design, and terrain, will affect the air infiltration performance of a window.   5. Will new windows be air-tight? 3245 Miracle Drive Murrysville, PA 15668 724-387-2991 PA Contractor ID PA001856