Indoor growrooms need proper ventilation in order to remove heat and odor. The use of exhaust fans with a high CFM (cubic feet perminute) rating ensures that hot air won't wilt growing plants. For odor control, the fan should blow stinky air through a compatible charcoal filter to scrub the offending molecules clean.
CO2 enrichment easily doubles or triples eventual yields. Plants need light, water and carbon dioxide for photosynthesis, and a lack of any one of these will bring growth to a halt. Maintaining a proper level of CO2 in the air can be tricky, since plants quickly use up all the available carbon dioxide. They stop converting light, water and gas into the sugars that build new cells. Adding extra CO2 allows plants to continue growing at an optimum rate at all times.
Tanks of gas are available from welding supply stores or beverage distributors, but the best solution is to purchase a CO2generator that burns propane or natural gas. Replacing the tanks is easy (they're widely available). Be sure to set timers so that exhaust fans are off when the CO2 is being added. This will avoid venting the expensive, CO2-rich air.