 The U.S. Department of Energy Building Energy Codes Program released a publication on June 19th, 2018 which detailed the requirements of a vestibule to be used in commercial buildings.The publication states it requires vestibules to reduce the amount of air that infiltrates a space in order to aid in energy conservation, as well as increasing the comfortability near entrance doors.By creating an air lock entry, vestibules reduce infiltration losses or gains caused by wind.