My first experiments with co2 were generating it by either the soda/vinegar or sugar/yeast methods. I found both to be messy, inconsistent, smelly to the point of visitors to the house commenting on it, and a constant maintenance hassle. If you're using yeast, you have temperature thresholds to monitor as well as everything else. I'm into low-tech and keeping things simple as much as possible, but I can't see the economy or pleasure of this type of co2 generation.

The heat-based methods (burning something to produce co2 exhaust) seem counter-productive: You're either compensating for the heat with some additional technology, or you're losing the benefit of the atmosphere enrichment through the stress to the plants. Please note that I've never tried to generate co2 by heat -- it just reasons out that way for me.

I'm just into my first "technical" experiment with co2. I don't have all the stuff in-hand yet to complete my latest method, but here is what it is:

20# bottle of co2 -- This is readily available through your local soda/beer bottlery or welding supply house. Up here a convenient 20# bottle is $30 initial cost, and less for the refill, since they charge a deposit for the container.

aquarium valve and regulator -- I got a Milwaukee MA957, available on ebay for under $100. This puppy has a hi and lo-side pressure gauge, a main regulator valve, and a secondary regulator needle valve for fine tuning the discharge rate of the gas. On the exit side of the needle valve is a 2-oz cylindar that is half-filled with water. The co2 discharges through the water, and then goes via tubing to the garden. The rate of discharge can be visually seen as bubbles in the water. There's an electric solenoid that stops and starts the gas flow.

This is really as much as a person needs to get co2 enrichment. It's not real precise, but it ought to be more reliable, controllable, and consistent than the other two types of generators mentioned above. I went a step further and bought a co2 monitor as well. This unit plugs into the wall and the solenoid from the co2 regulator plugs into it. It has a relay that will turn the solenoid on and off according to the (programable) ppm/co2 you want in the room. For me it's an economy measure that ought to pay for itself in a year with the savings in co2.

The sophisitcated growers get a total environment monitor that you can plug your fans, co2, lights, music, and prolly cigarette lighter and cell phone into. I figure I can duplicate the functions of one of these monitors with some simple 24-hour timers and surge strips.

But you say you don't have room for any of this shit. Please consider that the footprint of the co2 tank is about the same as the footprint of a gallon milk jug. It's taller of course. The monitor is 10"x10"x3" and is wall mounted. If you have the room to mix soda and vinegar, or to mix yeast and sugar, you have the room for this setup. If you don't have room for he tank in the grow area, you can put it somewhere else and pipe in the gas. It doesn't have to be close to the garden. Once you have your flow rate figured for the duration/cycle rate of discharge you want, it's a set-it-and-forget-it proposition.

I'll let you know how my experiment progresses as soon as I have the remaining piece (the monitor) in-hand.

Good luck!