After installing a whole house fan like the Ventamatic CX36BD2SPD, you should open multiple windows and/or exterior doors on the lower floors across different rooms or sides of the house to allow fresh air in, while keeping attic vents open for exhaust. Closing interior doors to unused rooms can help direct airflow. This setup creates proper cross-ventilation, enabling the fan to efficiently pull hot air out through the attic and bring in cooler air.