Marijuana Horticulture: The Indoor/Outdoor Medical Grower's Bible

remain open, divide the number of cubic feet of gas required by the flow rate. If the flow meter is set at 10 cfh, the valve will need to be open for 0.1 hours (1 divided by 10) or 6 minutes (0.1 hour × 60 minutes) to bring the room up to 1500 ppm. Remember, CO 2 leaks out of the grow room. On average, the CO 2 level of the room returns to 300 ppm in about three hours due to plant usage and room leakage. To maintain a steady level of CO 2 , split the amount of CO 2 released per hour into two or four smaller increments dispersed more frequently.
    Distribute the CO 2 from the tank to the grow room by using a tube or fan. Suspend lightweight perforated plastic from the ceiling to disperse the CO 2 . The tubing carries CO 2 from the supply tank to the center of the grow room. The main supply line is attached to several smaller branches that extend throughout the garden. CO 2 is heavier and cooler than air and cascades onto the plants below.
    To make sure the CO 2 is dispersed from the tubing evenly, submerge the lightweight plastic tubing in water and punch the emission holes under water while the CO 2 is being piped into the line. This way you know the proper diameter holes to punch and where to punch them to create the ideal CO 2 flow over the garden.
    Overhead fans help distribute CO 2 evenly throughout the room. The CO 2 is released directly below the fan into its airflow. This evenly mixes the CO 2 throughout the air and keeps it recirculating across the plants.
    Compressed CO 2 is expensive, especially in large grow shows. At roughly $0.50 per pound (450 gm), compressed gas is much more expensive than fuels used in generators. Cost of equipment and fuel make compressed CO 2 enrichment systems less economical than generators.
CO 2 Generator Systems
    CO 2 generators are used by commercial flower, vegetable, and marijuana growers. Green Air Products has introduced a complete line of reasonably priced CO 2 generators that burn natural gas or LP (propane) to produce CO 2 . However, heat and water are by-products of the combustion process. Generators use a pilot light with a flow meter and burner. The inside of the generator is similar to a gas stove burner with a pilot light enclosed in a protective housing. The generator must have a cover over the open flame. You can operate the generators manually or synchronize them with a timer to operate with other grow room equipment such as ventilation fans.
    CO 2 generators produce hot exhaust gasses (CO 2 + H 2 O). Even though CO 2 is heavier than air, it is hotter and therefore less dense and rises in a garden room. You must have good air circulation for even distribution of CO 2 .
    Carbon Dioxide generators can burn any fossil fuel–kerosene, propane, or natural gas. Low grades of kerosene can have sulfur content as high as 0.01 of 1 percent, enough to cause sulfur dioxide pollution. Use only high-quality kerosene even though it is expensive. Always use grade “1-K” kerosene. Maintenance costs for kerosene generators are high, because they use electrodes, pumps, and fuel filters. For most grow rooms, propane and natural gas burners are the best choice.
    When filling a new propane tank, first empty it of the inert gas which is used to protect it from rust. Never completely fill a propane tank. Propane expands and contracts with temperature change and could release flammable gas from the pressure vent if too full.
    Generators burn either propane or natural gas, but must be set up for one or the other. They are inexpensive to maintain and do not use filters or pumps. Hobby CO 2 generators range from $300 to $500, depending on size. The initial cost of a generator is slightly higher than a CO 2 emitter system that uses small, compressed-gas cylinders. Nonetheless, growers prefer propane and natural gas generators, because they are about four times less expensive to operate than bottled CO 2 generators. One gallon of propane, which costs about $2, contains 36 cubic feet of gas and over 100 cubic feet of CO 2 (every cubic foot of propane gas produces 3 cubic feet of CO 2 ). For example, if a garden used one gallon of propane every day, the cost would be about $60 per month. In contrast, bottled CO 2 for the same room would cost more than $200 per month!

CO 2 generators produce carbon dioxide by burning LP or propane gas. They also generate heat and water vapor as by-products.

Spray soapy water around all propane gas connections to check for bubbles (leaks).
    CO 2 generators