An improved, low cost conditioned air vestibule for use on a doorway of a refrigerated storage room permits unobstructed passage of vehicles while effectively reducing the exchange of air through the doorway and substantially eliminating precipitation both inside and outside the doorway by providing spaced inner and outer movable doors in a portal and extending across the doorway to define a closed entrance vestibule, and circulating conditioned air through the vestibule. Heated air is directed downwardly from adjacent the top of the doorway through the vestibule along substantially its full width and adjacent the surface of the inner or cold side door and air is withdrawn from the vestibule at the top of the doorway adjacent the outer or warm side door. The doors are spaced close together and actuators are provided for opening and closing both doors simultaneously to permit unobstructed passage of vehicles. Preferably, the doors are transparent strip doors permitting unobstructed vision through the vestibule while permitting passage through the doorway without opening the doors.