Hello,

There are many economical ways to get CO2 to your plants; I personally used these methods long ago with great results, way ahead of CO2 injection at that time....

1 - Channel your hot water heater or dryer (only if they use natural gas) exhaust to your grow room, the by product from burning natural gas is CO2.

2 - Buy one of those propane cylinders and attach a propane gas lantern (camping type) to the cylinder (buy and install a automatic shut-off valve for safety reasons), line the globe on the inside with foil so that unwanted light does not get to your plants if feeding CO2 at night/darkness, light the lantern at the lowest possible setting and wala you have CO2 which is the by product of the propane burning. This woud be used for something larger than a closet and usually last about 5-7 days non-stop or if you run it only when the lights are on... about 2 weeks

3 - For large operations that happen to be using a portable generator (no matter how large), you can get the generator changed over to use propane instead of gas, use all of the exhaust to feed your plants CO2

Good Luck