Air curtains create an invisible barrier to separate hot and cold air. Air curtains can also be used to prevent air or contaminants from moving from one room to another. Air curtains can be activated manually or automatically, based on temperature difference. In case of manual air curtain control, the air velocity can be adjusted via a switch or potentiometer. This can be done locally or remotely. For automatic air curtain control, temperature sensors measure the difference between inside and outside temperature and activate the air curtain if necessary.