The efficiency of air curtain in reducing infiltration and associated energy usage is currently evaluated statically by using an efficiency factor,ηair, based on single steady/static condition, which is often not the case for actual buildings under variable weather conditions and door usages. Based on a new method to consider these dynamic effects on air curtains, this study uses a dynamic efficiency factorηB in terms of whole building site end-use energy to assess the efficiency of air curtains when compared to single doors (i.e. without air curtains) and vestibule doors. Annual energy simulations were conducted for two reference building models considering their specific door usage schedules in 16 climate zone locations in the North America. The variations of the proposed efficiency factor for different climate zones illustrated the dynamic impacts of weather, building, unit fan energy and door usage frequency on air curtain efficiency. A sensitivity study was also conducted for the operation temperature conditions of air curtain and showed thatηB also considers these operational conditions. It was thus concluded that using whole building site end-use energy to calculate the efficiency factor,ηB, can provide more realistic estimates of the performance of air curtains operations in buildings than the existing static efficiency factor.