Studies influence on energy loss of an air curtain installed at building entrance. The energy loss consists of transmission loss and ventilation losses caused by stack effect, pressure difference due to wind, direct wind on the entrance and differences in the specific gravity of inside and outside air. Gives an example of calculated energy loss at the entrance of a simulated department store. Outlines principles and types of air curtain. Suggest that an air curtain can effect a saving in energy but that closing the entrance by means of a draught hall or revolving doors is the most economic solution.