A cross-flow fan is a type of fan that moves air from the inlet side to the outlet side by drawing air from the outlet side to the inlet side. The air moves in a cross pattern, or perpendicular to the direction of the blades. A cross-flow fan is best used in a location where a lot of air needs to be moved in a short amount of time. A cross-flow fan is most commonly used in commercial applications such as warehouses, factories, and other large buildings.