A method of calculating the aerodynamic characteristics of centrifugal fans that operate in a gaseous medium passes in the reverse direction. Mathematical formulas for calculating the value of the total backpressure created by the centrifugal fan of the geometric dimensions and the basic parameters of its work. Found experimental amended to allow with sufficient accuracy to calculate the characteristics of centrifugal fans with aerodynamic configuration «Ц 14-46». Examined picture of the flow and the patterns of distribution of the gaseous medium inside the volute casing of the fan at the inlet to blades of the impeller. Application areas are outlined of the proposed methods for calculating the reversing flow devices used in convection furnaces with a periodic change in the direction of the gas medium is reversed.