ANSI/ASHRAE/IES Standard 90.1 requires vestibules to be installed in buildings in climate zones 3 through 8 based on building energy simulations with a series of assumptions which can be avoided using a new method of airflow and energy simulations. Instead of vestibules, it is believed that air curtains can also reduce infiltration and the associated energy loss through building entrances. Therefore, this study proposes a method to estimate energy savings from vestibule and air-curtain doors for two U.S. Department of Energy reference buildings in 16 U.S. climate zone locations in terms of national weighted average energy savings and a sensitivity study of different contributing parameters.