Ventilation is one of the fundamental environmental factors that contribute to healthy indoor growing, but matching fan CFM with tent size can be confusing and we often get questions about which fan is right for given tents.
We’ve decided to write this blog post to help guide anyone needing a little advice on how to match your ventilation with your tent size.
Ventilation Equipment – Matching Tents and Ventilation
Your tent will require a few pieces of equipment to make the most of the ventilation, thereby refreshing the air inside your tent.
Inline Duct Fan – Matching Tents and Ventilation
An inline duct fan is used to push or pull air through your grow tent. This is important because it helps remove hot air, circulate refreshed air, remove excess humidity, and improve the fiber strength of your plants. Indoor grow tents are insular so temperatures inside can get much higher than outdoor growing and just like outside, a constant breeze keeps temperatures lower, which in turn leads to lower humidity levels so you will be able to control the overall environment easier.
The amount of air an inline fan can move is measured in Cubic Feet per Minute (CFM), which is how much air flows through the fan each minute. We will use CFM to match the fan with the tent size.
Ducting – Matching Tents and Ventilation
Ducting is another key component of ventilation. The primary use of ducting is to direct exhausted air. By connecting ducting to your fan, you will be able to force air into a specific area, whether that be into or out of the tent.
Ducting has a secondary use of muffling fan noises, if you decide to jump for insulated ducting—not a necessary add-on but a nice one to have! Also note, when calculating CFM, each bend in the ducting will increase your CFM requirements—keep reading for more information.
Carbon Filter – Matching Tents and Ventilation
A carbon filter is a great addition for anyone who wants to filter out unwanted smells that may emit from your plants. Carbon filters often come with felt or cotton covers for added filtration and an aesthetic look. If you do decide to include a carbon filter in your setup, you’ll have to organize your ventilation system in a specific way. You can check out how to organize your set-up by clicking the link below:
Matching Tent and CFM – Matching Tents and Ventilation
In order to know which fan matches your tent, we can create a simple equation.
First, we need to calculate the cubic feet of your tent, which is done by multiplying Length x Width x Height. For example:
This is our standard 4’ x 4’ x 6’8” (or 6.67 feet) tent. Let’s multiply this together:
L x W x H = 4 x 4 x 6.67 = 106.72 sq. ft.
If you had nothing else contributing to the ventilation requirements, you would only need a 107CFM fan to manage this size of tent, however, because we are including some other items in the tent we will have to change our equation. In general, growers estimate the following equipment to add higher CFM requirements to your fan:
Ducting: For each 90° bend in your ducting your CFM requirement will increase by about 40-60%, so try to minimize the number of bends in your ducting.
Carbon Filter: A carbon filter will increase your CFM requirement by about 60%.
Grow Lights: Due to heat output, your CFM requirement will increase by about 50% for LEDs.
Now, with all of this information, we can measure the approximate CFM required for our fan. The equation will be:
(cubic feet of space) x (ducting) x (carbon filter) x (grow lights) = CFM required.
107 x 1.6 x 1.6 x 1.5 = 410CFM
Check out the following chart to match CFM with tent size (this includes a calculation for ducting, LED lighting, and a carbon filter):
| Tent size | CFM required |
| 24” x 24” x 36” | ~46 CFM |
| 24” x 24” x 48” | ~62 CFM |
| 32” x 32” x 63” | ~135 CFM |
| 36” x 20” x 63” | ~95 CFM |
| 36” x 36” x 72” | ~207 CFM |
| 48” x 48” x 80” | ~406 CFM |
| 60” x 60” x 80” | ~634 CFM |
| 48” x 48” x 72” | ~369 CFM |
| 60” x 60” x 72” | ~576 CFM |
| 96” x 48” x 72” | ~737 CFM |
| 96” x 48” x 80” | ~811 CFM |
If you have any questions, please don’t hesitate to reach out to us!
And be sure to check out our other blog posts for useful tips on becoming a great grower!
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