The Air Change Rate Method estimates infiltration rates based on the number of air changes per hour (AC/hr). For commercial buildings, the range is 0 to 10 AC/hr, with higher rates corresponding to more exterior walls. For example, a building with one exterior wall might have an air change rate of 1.0 AC/hr, while a building with three or four exterior walls might have a rate of 2.0 AC/hr. Vestibules typically have a higher air change rate of 3.0 AC/hr.