NOTE 1 The centrifugal fan is also known as a radial-flow fan.NOTE 2 The impeller can have one or two inlet(s) and might include a shroud and/or a backplate (centreplate) (see Figure 16).NOTE 3 The impeller is defined as “backward-curved or inclined”, “radial” or “forward-curved”, depending on whether the outward direction of the blade at the periphery is backward, radial or forward relative to the direction of the rotation(see Figures 9 and 16).