ventilating-jack

from The Century Dictionary.

• noun A hood or cowl of sheet-iron, or some other thin metal, placed over the opening of a fresh-air inlet and directed toward the flow of the air in order to catch and induce a flow of it into the opening and so into the space to be ventilated.
• noun A similar hood or cowl over the outlet for foul or vitiated air, directed in the direction toward which the outer air-current is moving, so that a current shall be induced outward from the space to be ventilated.