This study investigates the energy saving impact replacing vestibules with air curtain doors (single doors fitted with air curtain units) has on energy usage of commercial buildings. Laboratory experiments were used to investigate the infiltration characteristics of air curtains in a small size chamber and to validate numerical simulation methods. Experimental flow and pressure as well as particle image velocimetry data confirmed that air curtains can significantly reduce air infiltration when compared to the single and vestibule doors. In addition, the results indicated that the CFD modeling methods used are valid in capturing the characteristics of the airflow at the door with air curtains. CFD simulations were conducted for a full scale door with consideration for the door operation cycle and the existence of people in the doorway. The results of the simulations were used to conduct energy simulations for two reference building models. The end use site-energy performances of the whole buildings with air curtain, vestibule and single doors are compared using two infiltration calculation methods. The energy simulations conducted show that, on a national average level, air curtain doors save energy (in comparison to code requirements). Finally, considering the space saving benefit of air curtains and their lower initial costs, air curtains are concluded to be a valid and energy saving alternative to vestibule doors in climate zones 3 to 8 and a valuable energy saving addition in climate zones 1 & 2
