the rule of thumb with fan's is that the center point that the blades are attached to or, the front, is the part where the air is sucked into. the back, the base that the fan is attached to and screws onto the case, is the exhaust side. follow?
It your choice if you want to put a side fan or just block it. Some say that it disrupts the normal airflow (front to back) but who knows. I personally use a low cfm fan as side intake in my antec 300 just to not cause too much turbulence in the video card area.
When in doubt - use a 9Volt battery and an old connector with the wires stripped and attach the red and black wires to those on the fan plug and the fan will run so you can check it !! ( the 9volt battery provides enough current to spin the fan but not enough to harm you or the fan )