A ventilator comprising an air blower; a casing comprising a first wall and a second wall configured to house the air blower centrally and to define a radially decreasing volume therebetween, a circumferential gap between the first wall and the second wall configured to allow a high velocity air stream to exit and to spiral in a direction away from a structure to which the ventilator is configured to be mounted, and a central opening in the second wall configured as a suction inlet of the air blower; and a flow amplifier adjacent the casing and configured to amplify air flow through an air flow passage defined between the flow amplifier and the second wall of the casing.