It's just a wood box about 24?x18?x36? where you have air drawn in through the top with a furnace return grill about 16x20. Next you get 5 medium quality filters the ones with screen mesh on one side are the strongest. You can use 5 to 10 pounds of active charcoal from the fish store for each layer. I use 5 but next time I think I will add one more. You make a charcoal sandwich and use gray tape to seal the sides and make it one big thick filter. You build the box so the filters fit tightly on all sides. You have a stop of about ½? trim all around the part where the filters end so you can keep them in place and tight but do not restrict the air flow through the filter.

Next you have a 12? air gap between the bottom of the filter sandwich and another plywood sheet you attach the high volume fart fan (bath room fan) to the underside. This is about 18? from the top going down overall measurement. You should have about 18? of empty space for the return air to fill so you drill 2? holes along the bottom of the box for return air back into the room.

The idea is to pull the air through the filters clean the air with the coal and return the clean air back to the room. Mine is in the ceiling and has a duck return system back into the room. You need to build the same thing but in a self contained wood box.
Zandor Reviewed by Zandor on . I should know better - but here's the dumb question anyway hi folks: i've done two grows in two years and have pretty much just paid attention to what was happening to my plants and used good judgment. HOWEVER, i have this question: when a plant description says 8-9 weeks for a flowering time, does that mean flowering will be at it's peak in 8-9 weeks? i just bought some nirvana white widow seeds and have seen some vegging for 10 weeks alone (which seems excessive). i'm planning an indoor grow with 125W fluoro (which worked tremendously well with Rating: 5