garden knowm is right. smell can be a huge problem, depending on the strain. i usually keep my rooms sealed, no ventilation. in that case i use a large carbon scrubber to recirculate the air in the room. inline ozone generators are decent, i'm just not a big fan of them. if you set your room up properly with three thousand watts, hydro, co2, and moderate your temp. you'll easily get 2.5lbs per light. three thousand wattts is much easier to control than four thousand watts. you can figure about ten degrees extra heat above ambient temperature for each thousand watts of light.