Abstract: A method for determining an air flow of an air handler including an indoor blower and a motor coupled to a heating, ventilation, and cooling (HVAC) system, includes receiving a signal indicative of an air flow at an extreme operating range of the HVAC system; receiving operational constants of the air handler, the operational constants representing performance characteristics of the air handler; transmitting a torque command to the motor; receiving a motor signal indicative of an operating speed of the motor; and determining the air flow using at least the operating speed and the operational constants.