I built a small grow cabinet 45'x22"x32" I can either buy a 3.25" axial fan or a 4.5". One has a 25cfm rating the other 125cfm. The problem I'm having is the small one seems maybe too weak, but the 4.5 seems like it could be overkill. I was going to just buy the smaller fan but I watched a DIY youtube video and the giuy used 4" 100CFM fans on a box much smaller than mine. Any help would be greatly appreciated Index bird
Give my Ventilation FAQ a read if you don't mind and give me a little feedback on if it helped make your decision. Short answer, when in doubt go with the bigger fan.
Id go with the 4.5". And like Bohbo's ventilation FAQ says, if you're worried, go with the little bit bigger size, it won't hurt