The closet is a closet that is under a set of stairs. I would say about 3 feet by 5 feet, probably a good 9 feet high at the tallest part. There is no exhaust fan, just a fan circulating air in the closet. The room that the closet is attached to right now is acting as a heat sink and air sink, with the closet door open 4 inchs or so. I'm kind of stuck with not having proper ventilation, as this is a rental and there is no easy way to hook up a fan that connects outside the closet. The plants seem to be growing real well right now. I'm about a week away from when I want to start flowering. I honestly wasn't going to bother with CO2, but the dry ice got me thinking that if adding some CO2 would make a large difference in yeild that I should try to do something. There is a cheap place to get dry ice where I live, so I figured that would be a low tech good way to increase the CO2. Is this a good idea or am I fucked until I get proper ventilation?