Inline fan/humidity

Hello fellow growers,

I have read optimal humidity during vegetative growth is between 60% and 70% RH. There is a humidifier running, and I have an inline fan set up in the grow room. When running the fan in the low position, humidity drops to 40%RH. Is the exhaust fan only necessary while flowering.

Any help or suggestions would be much appreciated.

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The exhaust fan is important for many reasons, one of which is to control air flow and proper c02 is getting to your plants. 40%rh isn’t bad for veg alot of people run that. If your plants are smaller right now you could put a dome over them to help hold moisture


Depending on the size of your grow space and the amount of CFM your fan can move(even at its lowest setting) will cause this problem. If you have a 2’x4’x6’ space( 48 cubic ft) and you have an exhaust fan that can move 220 CFM (110 CFM on lowest setting), you end up exchange the air 2-3 times per minute and nothing you add into that room will stay long enough to do anything.

I would turn your exhaust fan into an intake fan to your room (only during veg) and have an exhaust port/or hole at the lower section ( 2”-3” hole) of your grow space. The humidity will always rise upward before falling downward. Let me know if this helps you?


Thank you!

Thank you, I will try this out!

I actually have a small intake fan at the bottom, I will just reverse my setup while in veg.

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No worries bud, happy to help. If you need any help calculating exhaust and intake, let me know. I can at least get your clothes to watch your intake and exhaust equate to.