Airflow is part of the equipment's operating conditions
Homeowners often focus on the furnace, air conditioner or heat pump while treating ductwork as a separate issue. In a forced-air system, that separation is artificial: the equipment depends on the blower and duct system to transfer heating or cooling into the home.
If airflow is too low, a cooling coil may operate too cold, a furnace may run too hot and the equipment may not deliver its intended capacity. If distribution is poor, the equipment can operate while rooms remain uncomfortable.
Airflow therefore belongs in both service diagnosis and replacement planning.