Welcome to
The Exhaust Fan Calculator
In order use the exhaust fan calculator to figure out your type and size exhaust fan, you must consider the size of your garden area first. The general rule is to have an exhaust fan that will completely exhaust the garden area in less than 5 minutes. This is how...
Let's figure out the cubic feet of your garden area. Measure the floor of the area (example 3 feet by 4 feet), and multiply this by how tall the area is (example 8 feet). In this example, I would have 3 times 4 times 8, which equals 96 cubic feet.
Naturally, if I got a 96 cubic foot per minute (CFM) fan, I would be able to exhause the whole room in one minute.
If you divide this number by 5, you get the smallest CFM (cubic foot per minute) that you would want to go with. In my example, 96 divided by 5= 18.24CFM. An 18.24 cubic foot per minute fan is the smallest I would want to consider.
Now, to get a better idea of your fan needs, you need to look at your whole exhaust setup. Your light, your fan, and the way you move the air through the garden area are known together as your exhaust setup.
Reality Check
In reality, there are a number of things to consider that will affect the actual cubic feet that your fan will move each minute. These things fall into three catagories...
- your air exhaust duct runs
- your light reflector options
- the addition of a carbon filter
The exhaust fan is designed to move air FROM your garden area TO another area. In order to do that, you normally need to move the air through air ducts.
The minute you connect an air duct to your exhaust fan, the amount of air you can move (your CFM) drops. This is because it takes more energy to blow air through ten feet of air ducts than to just blow the air straight out the fan.
The longer the air duct run, the more your CFM will drop, especially if there are bends/turns. Try to keep it under 20 feet.
Your grow light reflector can block your airflow and reduce your CFM. This is critical information for anyone who wants to get started in the right direction. These detailed considerations can be found in my about your reflector section. I highly recommend you read these.
The above are all good reasons to get an oversized fan (one larger than indicated on the exhaust fan calculator).
Everything you have read up to this point can be accomplished with a squirrel cage fan.
With a Carbon Filter
If you decide to add a carbon filter, than a squirrel cage fan is not quite powerful enough to do the job well. You need the kind of air pressure only one kind of fan can deliver. You need a centrifugal fan. Your centrifugal fan will both filter your air, cool you lights, AND exhaust your garden area.
In addition, a centrifugal fan will maintain its CFM in many situations where a squirrel cage fan will not, so it is not neccessary to get an "oversized" fan. Simply follow whatever the exhaust fan calculator indicates to do.
The Setup
By now you have a good idea of where your garden will be, what light you will use, and what fan to use. Now it's time to put it all together. The next step is to design your exhaust setup.
Leave the exhaust fan calculator and
Continue to the Exhaust Setup Page
Leave the exhaust fan calculator and
Return to the Garden Design page
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