A radial fan (1) or centrifugal blower is provided having a fan housing (2) with a spiral pressure chamber (D) and a rotor assembly (10) comprising an internally axially open bearing tube (20), in which a shaft (40) carrying a fan wheel (30) is mounted with a rotor (50) of a canned motor. An air-guiding channel (L) between a first pressure-chamber region (2a) and a second pressure-chamber region (2b) of the spiral pressure chamber (D) is formed between the bearing tube (20) and the wall (W) of the canned motor, so that an air flow flows through the air-guiding channel (L) from one pressure-chamber region (2a, 2b) to the other and in the process dissipates heat from the bearing tube (20) into the pressure chamber (D).