As your plants "breathe" CO2 and "exhale" O2, the balance of these two critical gases begins to shift. In nature, this exchange fits in perfectly as animals "breathe in" O2 and "exhale out" CO2. Of course, a perfect world this is not. Modern industry and the burning of fossil fuels has somewhat "unbalanced" this effect. However, in your greenhouse or grow room, you will need to help your plants breathe by supplying a constant exchange of fresh air, which by nature contains about 2% CO2. If you have already employed a thermostat and humidistat in combination with a vent fan, there is a good possibility that these two mechanisms will provide a good exchange of fresh air. However, if your fan is not operating frequently enough, you may be starving your plants of their most important atmospheric gas, CO2.
Generally speaking, it is best to exchange the entire contents of your growing area about once an hour during daylight hours. To do this efficiently, you can use a fan that either runs continuously at a slow speed, or a fan that runs at high speed in short bursts. To determine the size of the fan that is necessary, simply multiply the length of your growing area by its height and then by its width. This number (use feet as a measurement unit) will be the Cubic Feet of your area. When buying a fan, you will notice that they are sold according to "Cubic Feet per Minute," or CFM ratings. What this means is the amount of air this particular fan will move in one minute. Therefore, if your greenhouse or growing room is 10 feet x 10 feet x 8 feet, that's a total of 800 Cubic Feet. You will need an 800 CFM fan to exchange the air in the entire greenhouse in one minute. That's a big fan and you certainly don't need to move it all out in just a minute's time. I would suggest using a 100 CFM fan and running it for 4 minutes every half hour. You can do this with a cycle timer.
Was this article helpful?
You Might Just End Up Spending More Time In Planning Your Greenhouse Than Your Home Don’t Blame Us If Your Wife Gets Mad. Don't Be A Conventional Greenhouse Dreamer! Come Out Of The Mould, Build Your Own And Let Your Greenhouse Give A Better Yield Than Any Other In Town! Discover How You Can Start Your Own Greenhouse With Healthier Plants… Anytime Of The Year!