An air mixing device mitigates temperature stratification between two incoming air streams by creation of turbulent airflow through an arrangement of channels in the device. The device also provides selective passage of air for incoming airstreams to achieve functionality for damper control typically associated with separate inlet dampers. A method provides for selectively controlled airflow through the device so effective mixing occurs along with an economizer function to control separate airstreams such as outside air and return air. Existing dampers may be integrated with the air mixing device to control airflow in which flow of one airstream through the device increases as the flow of the other airstream is proportionately decreased. A minimum outside air duct can be incorporated in the mixing device to efficiently satisfy building code requirements regarding monitoring and recording of outside air input to air handling units.