I have an idea if it isin a corner like I think it is. OK bear with me. The back wall of your grow box(which I assume is facing the corner leaving a triangle of empty space behind it) Take that back wall off and put the fan right in the corner. It will suck the air down the empty space and direct it into the box. The only thing is that you will have light shooting up out of the corner. It should help a little. It would help more if you could open the side coming out towards the room, even a 4" hole would allow for the air to flow out a little better. The only othe tip I can give yu is that light can't bent so if you get your hands on some flexible dryer tubing and bend it 90 degrees light will not escape but air can travel through, but it does restrict airflow. I gotta update my log though I'll pop in later.