"Exhaust Fan" by intake and exhaust ports are divided into wall type (partition wall holes are free space on both sides, from one side wall to the other side of the ventilation), the catheter exhaust type (from the side of the free space intake, while the other side through the exhaust conduit), - inlet ducts (intake side through the conduit, and the other side to the exhaust gas free space), the whole conduit type (fan duct disposed on both sides, by intake and exhaust ducts). Press into the form of a centrifugal air flow (air from the direction parallel to the axis of rotation of the entry, in the direction perpendicular to the discharge axis), axial flow (air to enter by a direction parallel to the axis of rotation, still parallel to the axis of the discharge direction) and cross-flow type (air inlet and outlet are perpendicular to the axis).