If you plan on having a closed environment (e.g., grow room, grow tent, etc...) then you need to properly ventilate your growing environment to ensure your plants yield up to their potential.
Proper ventilation helps regulate humidity and temperature in your grow room by exhausting the warm air that your grow lights and electronic equipment are producing. Cycling out this air also provides relatively carbon-rich air for your plants to breathe better, which will help them yield more.
Many websites give a blanket rule-of-thumb for CFM calculation that fails to take into account the uniqueness of each growing room. Below we will show you a way to calculate CFM taking different aspects of your growing environment into account to give you the minimum CFM recommended for your grow room.
Growing Environment Volume: Calculate the volume of your room by multiplying the length x width x height. For example, if you have a grow tent that is 8' x 8' x 7', then the volume would be (8x8x7) = 448 cu./ft.
Volume To CFM: Your exhaust fan should be able to exhaust the equivalent of your growing environment's volume in two minutes, or one minute if you are having issues with high temperatures. Assuming we are not having issues with heat, the growing environment volume from our example is 448 cu./ft., which means we need to exhaust 448 cu.ft. / 2 minutes = 224 CFM. From this I know that I need a 224 CFM fan at a minimum.
Other Variables To Account For: We're not done yet. Now to account for other variables that can require you to have more CFM required for your grow room:
- Lights: For each air-cooled light (600-1000w) add the equivalent of 10% of the calculation you finished in the 'Volume To CFM' step. For non air-cooled light add 20% per light.
- CO2: Add 10% for rooms with CO2 enrichment via a CO2 burner or generator (they create heat).
- Carbon Filters: Add 20% if you're using a carbon filter.
- Ambient Temperature: For hot climates (Southern California, Arizona, etc...) add 25%. For humid and hot climates (Florida, Georgia, etc...) add 40%.
Let's run through a full example of calculations accounting for each one of the four variables noted above. Let's still assume we're using the 8' x 8' x 7' grow room used for the example above. We're at 224 CFM before we jump into adding in the accessories, so that will be our starting point.
Let's now assume the room has two non air-cooled 700w LEDs, a CO2 burner, a carbon filter and we're located in Southern California.
Lights: Add 20% per light x 224 CFM = 48 CFM. 24 CFM x '2 lights' = 96 CFM. Add the 96 CFM to your calculation of 224 CFM to give you 320 CFM.
CO2: Add 10% x 224 CFM = 24 CFM. Add this to your 320 CFM to give you 354 CFM.
Carbon Filters: We are using a carbon filter to remove odors, so we'll add the 20% x 224 = 48 CFM. Add this to our 354 CFM to give us 402 CFM.
Ambient Temperature: We're assuming we're in Southern California so we're going to add 25%. 25% x 224 = 56 CFM. Add that to our 402 CFM to give us 458 CFM.
Our final calculation gives us 458 CFM in this example. Remember that this is the minimum amount of CFM we'd recommend for a grow room with all of these parameters. That said, we would want to shop for a fan with higher CFM than 458 and we can always use something like a fan controller or fan speed controller to adjust the speed down if needed.
In this example, I'd personally recommend going with a 8" fan that produces between 550 - 800 CFM and would adjust the speed down until it hit the sweet spot of temperature and humidity.
First make sure to unplug your fan. Then go outside or lay down a tarp or newspaper inside to collect the dirt and debris. You'll want to get a damp cloth and wipe the blades and the inside of the exhaust fan. Next you'll want to take a can of compressend air and spray the inside of the fan in those hard to reach areas that you couldn't wipe down.
Make sure the fan completely dries out before you re-install it and turn it back on.