CO2 is heavier in concentration than regular "room" atmospheric air. It needs to be released slightly higher than its intended target plants. You can see the problem in dispersal immediately. Therefore treat it like water. Release it where it is needed or where it can follow a path to the canopy.
Uh oh, what about ventilation? I'll take ventilation with good total room air exchange every 5-10 minutes and heat control over supplemental CO2. In small grows I am saying right now CO2 is a luxury and far from a proven necessity. The CO2 (which is NOT cheap!) will exit the room as quickly as the rest of the air.
Now, as a positive side to global warming (maybe the only one) is the increase in CO2 in atmospheric air. Due to people, internal combustion engines, melting of permafrost in the Arctic (HUGE releases here). In short - screw CO2. Focus on ventilation and cooling. Control and provide those and the plants will reward you more than with CO2.
Saying this as a welder who grew up in a welding shop. That drove me into medicine but I still weld. TIG/MIG/DC. LOTS of CO2 around and trust me, I've used it. Lug those damned huge "K" cylinders to the gas company for refill. Load it, rolls allover your truck bed smashing stuff. Break your back and buddy THE PAYOFF IS NEGLIGIBLE! Buy a bag or two of ExHale and hang them over your grow. Good luck.
