Abstract: An in-line centrifugal fan including a housing having an inlet and an outlet spaced apart and substantially coaxial one to another and a motorized centrifugal-type impeller mounted centrally within the housing substantially coaxially between the inlet and the outlet. A plurality of spaced air flow redirecting vanes are each connected to and radially extend inwardly from the housing toward, but not to, a radially outermost perimeter of the impeller whereby air flow through the housing is increased by the vanes. Various vane configurations, clearances and number of vanes are disclosed.