Rotor-only ducted axial fans with small hub-to-tip diameter ratio are widely used in many branches of industry, especially for cooling and ventilation purposes. For such fans, extensive regions of backflow are present downstream of the fan near the hub. Only few computational fluid dynamics (CFD) studies for such fans have been reported in the scientific literature. In order to develop guidelines for obtaining accurate CFD predictions for such fans, validation simulations of a fan with small hub-to-tip diameter ratio have been performed by comparing experimental and computed aerodynamic performance characteristics. These guidelines pay special attention to the trailing edge shape, presence of nonaerodynamically shaped blade sections, tip gap, and employed turbulence model. The results for the fan studied here show that the actual (rounded) trailing edge is necessary; the main blade (without nonaerodynamically shaped blade sections) well represents the aerodynamic performance of the whole fan blade; it is recommended not to take the tip gap into consideration due to the existence of significant flow separation; the use of the Spalart–Allmaras turbulence model is advised for giving better agreement with measurements.