Grow Room CO2 Setup

by Bobby Mercer

I'm pretty new to the indoor garden game. My grow room is 7 ft by 5 ft by 8 ft tall. It has a 1000 watt HPS running for 12 hours day with a six inch exhaust fan pulling air from the room outside of it (which is keep at about 68 to 70 degrees). My grow room temp stays at 82 as long as it does not get insanely hot outside. Still, it has only been 90 degrees once. The room is also air tight if you where wondering. My question is how do I go about setting up my CO2? I have the tank, I just need to get everything else....I need to get started, please let me know.

Answer: Bobby- your grow room is still running a few degrees on the warm side. If possible, I would try ventilating the grow light with it's own exhaust fan, pulling air from somewhere outside the room, through the enclosed light fixture, and exhausting it somewhere outside the room. If you are running your exhaust fan constantly to keep the room cool, this makes it very difficult to increase the CO2 levels inside the room. The best solution for CO2 supplementation is to have your grow room air conditioned and the grow light ventilated separate from the rest of the room.

If you can get your room temperature to the point where there are appreciable spaces of time in between exhaust cycles, then here is how you set up your CO2....first, you will need a pressure regulator and a flow control valve. The pressure regulator takes the pressure in your CO2 tank (which can be 1200 psi) and steps it down to about 50 or 100 psi, which your solenoid valve can handle. The flow control valve can be adjusted up or down to control how many cubic feet per hour (CFH) of CO2 is released. The solenoid is simply an open and close style release valve that can be electronically controlled by either a timer or a digital CO2 controller.

Attached to the solenoid is plastic tubing, often called laser tubing. It has very tiny holes manufactured in it (by lasers) that allow the CO2 to be evenly dispersed along the length of the tubing. Since CO2 is heavier than air, the tubing should be placed evenly around the garden above the tops of the plants. The only thing you have left to do is adjust the CFH of your flow control valve and set your timer, or else plug the solenoid into a digital CO2 controller.

Controllers can be expensive, so many growers decide to go with the timer method. For these calculations you will need to know the volume of your grow room, as well as the desired level of CO2 supplementation. On my Plant Growth and CO2 page I walk you through all of these calculations step by step. For this example I will use your garden dimensions, and our goal will be to bring the room up to 1500 ppm CO2 (a fairly common level of supplementation).

Your garden is 7 x 5 x 8, which equals 280 cubic feet (the volume of your garden). CO2 levels in the atmosphere are normally around 300 ppm, and our goal is to bring the grow room up to 1500 ppm. Therefore, we need to increase the CO2 levels by 1200 ppm (or .0012). We calculate the amount of CO2 we need to release into the garden area by multiplying the increase (.0012) by the garden volume (280). In this example, we will need to release .336 cubic feet (CF) of CO2 to reach our goal of 1500 ppm. For convenience, I am rounding this number up to .34 CF.

In this example, if you set your flow control valve to .34 CFH, and programmed your timer to open the solenoid valve for one hour, you would slowly bring your grow room up to 1500 ppm CO2. This will only work if your exhaust fan does not kick on in the meantime to lower the room temperature. In reality, you should set your exhaust fan to kick on when the room reaches 85 or 87 degrees, and to kick off when the garden reaches the ambient air temperature. Now time how long it takes before the exhaust fan kicks on again.

For maximum plant growth, you want all of your CO2 released by the time you are 1/2 way to 2/3 of the way through this time period. If you have 10 minutes in between exhaust cycles, then it is a good idea to release all of the necessary CO2 within 5 minutes.

Your flow rate and the amount of time you take to release it share an inversely proportional relationship. This means if you take 1/6th of the time to release your CO2, then you will need to multiply your flow rate by 6/1 (which is simply 6) in order to end up with the same level of CO2 supplementation you began with.

5 minutes is actually 1/12th of an hour. In order to release the necessary amount of CO2 in this time, you need to multiply the original flow rate in this example (.34) by 12. This gives you a flow rate of 4.08 CFH. Now you can set the flow control valve on your tank to 4.08 CFH, and set your timer to open the solenoid for 5 minutes immediately following the end of each exhaust cycle. An even more efficient setup would be to get an atmospheric controller which would monitor temperature, turn your exhaust fan on and off, and also release CO2 after each exhaust cycle. Hope this helps Bobby, and Happy Growing!

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