If I vent my fan out of my grow box through a duct that goes into my attic and split it onto an existing exhaust out the roof would I even need a carbon scrubber. I have a 3'x2'x4' box and plan on using a 4 or 6 inch ventech fan with a speed controller. The duct from the top of box to the fan would be about 6 feet then about 15 feet of duct from fan out to roof. I live in a neighborhood where the houses are about 20 ft apart. I will have two to three plants going at a time.