Ring Blower : A side channel blower of the type used as a combustion air blower for motor vehicle heaters wherein a vaned impeller compresser air within a channel formed in a blower. The blower hosing has an inlet opening and a discharge opening, between which there is a cross piece. In order to increase the compression pressure which can be achieved with the side channel blower, the inlet opening is in an axial plane and empties into the side channel in the direction of rotation of the impeller. Furthermore, the cross piece has a substantially uniform length in the circumferential direction of the flower and extends into close proximity to a boundary edge of the inlet opening that extends across the flow channel so that anaxial projection of the inlet opening onto the plane of rotation of the impeller is as small as possible relative to the area of the inlet opening in the axial plane. To adjust the output of the blower, a bypass opening is probided in the wall of the side channel, at a poing from approximately one-third to one-half the circumferential distance toward the inlet open from the discharge opening. In this way, a blow delivery characteristic can be achieved with the bypass opening open that is substantially directly proportional to that achieved with the pypass opening closed.