I have a 8ft High 4ft x 5ft grow closet. The temps with no exhaust fan are 89 degrees. I was wondering if a 6" in-line duct fan would be good enough for the room that has 1 feet of ducting going to a vent that is in the grow room door would be sufficient enough? Or I have 2 of these http://www.frys.com/product/7190142?site=sr:SEARCH:MAIN_RSLT_PG could I just add one of them to the end of this http://www.homedepot.com/p/Master-Flow-10-in-x-4-in-to-6-in-Universal-Register-Box-RB10X4X6/100200159#.UmrTOnCsh8E which is connected to my vents. Which should I add to the duct?