This test method measures air leakage associated with the window assembly. A sheet of plastic is adhered to the exterior face of the specimen. An airtight chamber is built on the interior of the specimen, the chamber is then put under a vacuum at a specified pressure, and the air leakage is measured and recorded. Then, the plastic on the exterior is removed, and the air leakage is measured and recorded for a second time. The difference between the recorded airflows is the air leakage of the specimen. This test passes if the air infiltration rate is lower than the maximum allowable rate.