An HVAC system includes a blower. The blower includes a driven pulley and a motor with a driver pulley. A motor drive supplies electrical power to the motor. A controller receives a benchmark rate of the flow of air provided by the blower and a corresponding benchmark output current of the motor drive. A benchmark input power corresponding to the benchmark output current is determined based on a predetermined relationship between input power and output current for the motor drive. A ratio of the benchmark rate of the flow of air provided by the blower to the benchmark input power is determined. The controller determines a pulley ratio for the blower based on this ratio.