Noise heard by passengers due to the HVAC system involves many sources and paths. The blower is a radial fan that generates noise from the interaction of the moving blades with the surrounding air, and the impact of the moving air on nearby static components. This fan noise is acoustically propagated through the complex network of ducts, out of the registers, and into the cabin. The duct and mixing unit airflow noise sources are generated mainly by flow separations and vortices resulting from airflow past the detailed geometric features, and are also acoustically propagated through the system. Noise due to the flow exiting the registers depends on the fine details of the grill and its orientation, and the resulting outlet jets that mix with the ambient air and can impact a solid surface (such as defrosting the windshield). Therefore, the requirements for the numerical flow-acoustic prediction are challenging and include handling of very complex geometry, prediction of fan- and flow- induced noise sources, and their acoustic propagation all the way through the system to the passenger locations. Accurate prediction of fan noise has been a key challenge and an unsolved problem in the field of aeroacoustics.