Abstract: An axial flow fan operates with increased efficiency, reduced noise, and improved resistance to stall. These benefits are achieved by providing a fan shroud with a bellmouth and a hub with a curved bellmouth wherein both have a substantially parabolic shape, and by providing a blade shape with an air pressure distribution that promotes smooth airflow and resists stall. The blade is provided with a twist that varies with distance from the blade root such that the work done on the air moved by the blade, whether at the blade root or tip, is substantially equal.