Looking at your floorplan/schematic I think that the open window, next to the fan, in the kitchen, is hurting airflow. It is likely that your predominant air f

Looking at your floorplan/schematic I think that the open window, next to the fan, in the kitchen, is hurting airflow. It is likely that your predominant air flow is right in that window and right out the fan. You could probably establish a much longer - and more useful - flow if you closed that nearby window and left the dining room window open. It's not certain - flows and turbulence do weird things - but it's worth trying.