There are two ways to use an air curtain. You can use it in an open doorway, in which case a stream of air runs continuously. You've probably felt the puff of air from this type of air curtain when you've entered a big-box, warehouse-style store. Or, you can use the air curtain as a second line of defense behind a closed door, in which case the air curtain is activated only when the door opens. It springs into action, blasting air for a couple seconds until the door is again closed.
In both cases, the curtain is mounted on the heated/air-conditioned side of the doorway, extending across the length of the door opening. Its intake sucks in conditioned air and blasts that air either straight down or at a slightly outward-tilted angle (see more on next page) to push away any outside air that otherwise would enter through the doorway.
An air curtain can be augmented with an electric heater. Imagine walking into a building on a freezing winter day to feel a cascade of heated air. And speaking of heat, because hot air tends to pool by the rafters, an air curtain also helps re-circulate that heated air. The current of air is also strong enough to fend off flying insects, dust, pollution and any other unwanted contaminants [source: AirDistributors.com]. In fact, some businesses use air curtains for the purpose of keeping airborne contaminants from sneaking into sterile spaces. And curtains can even be used to guard open ovens and freezers.