When consumers begin searching for new windows, there are two ratings that are commonly provided by the manufacturers, and used for comparison of windows: U-Value and Solar Heat Gain Coefficient (SHGC). While these ratings are important, they don’t tell the whole story on a window’s efficiency, and more importantly, the durability of the window.
Air Leakage Ratings (AL) are every bit as important as U-Value and SHGC, but it’s typically a rating that is much harder to obtain from manufacturers. That is, unless a window has a stellar rating. AL ratings are obtained by closing and locking the sample window and then applying a 25mph wind to the exterior, while testing to see how much air leaks through the window. Since one of the primary expectations of new windows is keeping indoor air in and outdoor air out, identifying a particular window’s AL rating is critical to determining the overall efficiency of the window.
The American Architectural Manufacturer’s Association (AAMA) requires a window to have a AL rating of .30 cfm/ft² or lower for certification. Most vinyl windows are rated between .12 and .24, but a high performance window will have a rating of .05 or lower. Okna’s Enviro-Star double hung vinyl windows have the industry’s best rating of .01 cfm/ft². That’s really tight! And that tightness means better efficiency, better noise reduction, and less dust in the house.