Some people.
There's no need for carbon in a filter bringing air in tho the air should be filtered pretty finely to prevent intrusions by nasties of all sorts. It would be easy enough to DIY a great filter with cut up HEPA vacuum bag filters for the ultimate in filtration but no need to go that far really. You would need about 10x the area of the intake to get decent flow thru even regular vac bags. The filter itself could be inside if designed to work like an inline filter.
I'm planning to use a furnace filter at one end of the new 8x4' grow space I'm adding on to my current room. All my air comes in from the basement and is cool even in the summer. I'll put a layer or two of cheesecloth over it and just change that out once in a while tho there's very little dust down there. 10x30' concrete box with my current room taking up 7x9ft in one corner. Built as a cold room it has well insulated walls other than the two outside walls that just have 1/2" OSB on them. I'll be running two 600W HPS on a light rail to flower lots of girls in there.
I have my exhaust fan running on a temp/rh and speed controller so it's not running all the time. RH is always low here so want to keep the air in until it gets too warm. I burn an alcohol lamp in there to keep CO2 way up as just one 600 isn't enough to heat the room up to trip the fan but once an hour.
It can be a real juggling act to keep everything dialed in sometimes but getting easier all the time.
Whatever I’m only looking to have 5 flowers plants out of these..
