Abstract: A heating, ventilation, and/or air conditioning (HVAC) system includes a variable-speed fan comprising a first fan blade, a variable frequency drive (VFD) configured to drive the variable-speed fan to rotate the first fan blade at various speeds to deliver a first airflow at variable airflow rates, and a constant-speed fan having a second fan blade. The HVAC system also includes a fan motor of the constant-speed fan configured to rotate the second fan blade at a fixed speed to deliver a second airflow, and a controller configured to determine an operational combination of the variable-speed fan and the constant-speed fan that achieves a target flow rate with a combination of the first airflow and the second airflow without operating the variable-speed fan in a stall region based on stall region data for the variable-speed fan.