Placing boundary condition fan on ejecting side

[athomas]

Hi
I am doing analysis for a mechanical room to study the forced stack effect. The wind is forced into the space through by fans placed in front of louvered openings on both sides of the room at floor level. There is an opening at the clerestory level and a fan facilitates the exhaust. For boundary condition properties, I have defined the type as fan with flow data and defined boundary. For supply windows the boundary arrow look right, but I am unable to get the exhaust arrow correctly.
The program automatically directs the user to the interior side of the wall when you go down a level. So how do I draw the fan boundary on the ejecting side of the exhaust ie external wall side.
Pls help