A centrifugal blower system includes: a) a series of blower units, each blower unit in the series comprising a casing having an axial inlet and a radial outlet, an impeller disposed within the casing for drawing a gaseous medium at a first pressure into the inlet and expelling gaseous medium at a second higher pressure through the outlet and a motor for driving the impeller; and, b) a duct connecting the outlet of at least one blower unit in the series with the inlet of at least one other blower unit in the series.