Vortex control can be supplied on most fans for accurate and efficient volume regulation, so necessary for most combustion air installations. This device consists of movable blades mounted in the fan inlet ring and arranged to produce variable velocity of approach of the air entering the fan wheel. This arrangment produces volume control superior to other low cost methods, as well as increased power savings. Close regulation with Vortex control is effective from full fan performance, down to approximatly 20% of full volume.