I like fanning in outdoor air from another room near the grow when it's cold enough outside to get away with it...This air contains between 0.03-0.04% CO2,(300-400 PPM),that naturally occurs in the air...Think I'm also gonna go back to fanning in some CO2,probably with the disposable CO2Boost,as I'm a ghetto grower who grows with an open closet during "lights on"...:420thought: