The ASHRAE Applications Handbook states that air curtains/air doors are local ventilation devices that supply a high-velocity stream of air to reduce airflow through apertures in building shells, as well as many other applications. The terms "air doors" and "air curtains" are often used interchangeably in the HVAC industry. Whichever term is used, there is generally no difference in the equipment that is specified. This article will use the term "air door" to mean air door and/or air curtain.