ive never heard of dividing it in 3. is there a formula behind why its 3?
in my experience an inline fan with a speed controller is going to do loads of help. you can then adjust and dial in the proper speed that you need.
CFM is pretty straight forward as its literally cubic feet per minute. so for example i have a 6inch exhaust fan with a rating of 442 cubic feet per minute and my tent is 104 cubic feet (4x4x6.5)
so you would assume that i would only need to be set at roughly 1/4 strength. but you also have to take into account the movement of the air being exhausted and also how often you would like the air to be changed in your tent ( some say 3 times a minute and some say 1 time every 5 minutes is just fine. it will eventually be up to your environment and its needs). distance of ducting and how many turns are in the ducting like 90 degree turns are also factors that reduce your fans efficiency . also having a carbon scrubber is going to reduce CFM as well and whether or not you are pulling or sucking air. i run my exhaust at 50 percent and sometimes slightly higher if its a warm day out. i maintain 50 percent humidity with that setting....i have yet to reach the decision on whether im just going to kick it up a notch to kill the humidity or if im going to invest in a dehumidifier....but i can tell you that i will prolly just try to kick it up a notch because i dont want the hassle of emptying the water tank off the dehumidifier, but thats just me.
i hope that helps....oh also if you want some science behind CFM ( im a big fan of learning the actual reasons why and how)
http://contractingbusiness.com/service/use-air-changes-calculation-determine-room-cfm
this site helps with contractor building for tonnage and AC (air change) requirements for residential and commercial buildings. just omit the part where you multiply the CFM by 60 to get CFH ( cubic feet per hour) and you will have your self a nice and accurate plan of how to tackle exhaust and air changes
happy growing and of course read read read practice practice practice rinse and repeat
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