What to Know About Air Infiltration Ratings
Air infiltration is rated by the industry standard ASTM E283 air infiltration test, which measures how many cubic feet of air passes through the window per minute in relation to the size of the window. Looking to meet ENERGY STAR minimum requirements? Look for numbers lower than .30 cfm/ft2. The difference in ratings between various operable windows will vary by manufacturer, but to add context, Siverhus notes that for Marvin, all three of the window styles mentioned above are well below minimum requirements for air infiltration, with the Ultimate Casement Window coming in at less than 0.01 cfm/ft2.
If you want to make an apples-to-apples comparison, ask your window dealer for the air infiltration ratings on the windows you’re considering buying for your next project.
Prevent Unnecessary Air Infiltration
Windows are tested using the exact manufacturer’s installation guidelines. If installed incorrectly, even the highest performing window can be doomed to underperform. Follow installation instructions to the letter, and be aware of other factors that could affect the performance of the windows you’ve so carefully installed. Have a conversation with your painting contractor. Let them know that oil-based stains and finishes will cause weather stripping to harden prematurely, which will reduce their capacity to prevent air infiltration.
Keep in Mind – Windows are only part of the solution
Managing customer expectations is key to every successful project. Well-built windows can reduce a home’s energy bills and increase comfort levels, but energy efficient windows are only one component in creating a tight and energy efficient building envelope. A homeowner is bound to be disappointed if they pay for the highest quality windows that end up having very little positive impact on comfort levels because the house has no water resistant barrier, poorly insulated walls, and is riddled with attic air bypasses.
Take what you know about the energy-saving qualities of various windows and glass packages, and ensure they are one component of a host of efforts and improvements to the overall energy efficiency of a home.