No Lion you read it right. I dont have an exhaust line. I have two lines in. One 6" line running thru the hood and then thru the ceiling. The second line is a 4" line that just brings in fresh air. What are my options? Can I just reverse the fan and run it thru the ceiling too? Or do I need to get another fan and leave the fresh air one in too?If I got a fan and carbon scrubber could they both in the same room? The scubber would clean the air and dry the moister out of the air at the same time?
You have all sorts of options... and this is just a suggestion or two based on my own experience and formed opinions. There is lots of info out there on this subject and so many variables that your final solution will likely be unique.
If you aren't running CO2, then simple ventilation is all you need - intake and exhaust. It's great the way you have your sealed hoods - drawing in cool air from another room and exiting up through the ceiling. The 4" intake fan you have is also good - especially if the room does not have a natural inlet for fresh air such as an open door. You need to get an exhaust fan to match the size of your room, so that the air in your room can be exchanged with fresh air in a reasonable amount of time. If your room is not large, you may be able to use your current 4" intake fan as exhaust, though 4" fans with can filters are usually reserved for huts and closets. You will likely need a 6" or 8" fan minimum, if you want to hook it up to a can filter and exhaust up through the ceiling. You can try your 4" fan as exhaust and see if the negative vacum created exchanges enough fresh air naturally. Most rooms have plenty of cracks and spaces around windows and floor boards to allow fresh air to enter. Your current hole for intake will likely work well to allow air to enter your room.
The scrubber really just removes odor from the air. They are most effective when humidity is below 55%. At first, see if you can get away with just the can filter on your exhaust. If odor is really a concern, then you will need to scrub too (or use some other sort of odor control).
CO2 and a sealed room is the way Stink rolls. In that case, exhaust is really just for emergency venting. With sealed rooms, AC and deumidifiers are usually required to keep temps and humidity in check.
Again, please look at all your options, as there are many solutions.