The air leakage measured using the laboratory test of fenestration is important to gauge its initial performance and for certification. Field testing based on a statistical approach was carried out in this study on newly installed fenestration product to study the nature of distribution of air leakage measurements. The measured values from these tests were also compared to the laboratory tested value of the same product and to the values as suggested in field testing guidelines as provided in AAMA 502. Results indicate that field measured values at standard pressure difference follow a normal distribution with a mean and a variance. The results also show that while number of test results fall within a certain range of the laboratory value and the AAMA 502 stipulated value, there are number of values that are higher than them.