I use a small closed space, with an AC to regulate my temperatures from my lights so no exhausting air to the outside or intake into my grow room. Around the door and sockets I have sealed, and now this allows me a more efficient use to a 20 lb. tank with a CO2 controller to regulate the levels in my grow room to about 1000 ppm during lights on. This is not a cheap investment, but their are other ways of adding supplemental CO2 which would help somewhat, but again their is a cost associated with it to be effective. A 3 x3 space may not be worth your costs, but go ahead and look at your options if you so desire.