Abstract: A heat generating device includes a sealed metal drum with spaced peripheral fins and houses a cage-like agitator mounted on a rotatable shaft axially disposed therein and extending through one end for connection to a source of power. The agitator includes a plurality of elongated flat bar-like vanes arranged in close concentric relationship to the drum and supported by spaced apertured hubs on the shaft. The periphery of each hub has serrated type notches so that the vanes are tangential to the hubs and in off-set alignment with each other. Relative to the direction of rotation of the agitator, the leading edge of each vane is spaced inwardly from the trailing edge of the adjacent vane a predetermined distance to provide a restricted passageway.