An air purifier having a polygonal casing defining one or more inside corners, a cylindrical air filter extending along a center axis within the polygonal casing with a space formed between a radially outwards facing surface of the filter and at least one of the one or more the inside corners of the casing, and a filter cleaner at least partly located in the space. The filter cleaning has a cleaning member, a gear mechanism, at least one UV light source, a motor configured to drive the gear mechanism to thereby drive the radially outwards facing surface of a cylindrical air filter past the cleaning member and the at least one UV light source, and a filter cleaner housing encasing the motor, the cleaning member and the gear mechanism.