First timer here. I would imagine that the a fan runs constantly during flowering, but what about at the other stages of growth, from seedling to veg? I currently have a bunch of seedlings in a large rubbermaid grow box that exhausts out the top with an in-line fan, with inlets on the lower sides. How much does it need to be on during this period, I would think the constant air movement might dry out the space?

Thanks!

You Need To Have Your Oscillating Fans Going 24/7, The Exhaust Fan's Or If You Have Vented Hoods & Inline Fans Need To Run While The Lights Are On (i like to have them set where they come on 30min before light on & 30min after they go off), If It Is Just A Exhaust System For The Grow Area They Would Need To Do The Same While The Lights Are On, If You Live In A Real High Humidity Climate You Will Want To Have The Exhaust System Come On Every Few Hours For 15-to-30min To Refresh The Grow Area & Keep The Humidity Down.
You Can Tweak You System For What Works Best For You, This Is Just A Guide-Line That Works Good For Me.

Hope It Help You As Well...

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agree with Hatch here. definitely when the lights are on you should keep the fans going to keep down the temp. i would suggest to keep all your fans running 24/7, but if you want the intakes to switch on/off every 15-30 minutes while the lights are off i guess your plants will be fine. the air flow is needed for bringing in the fresh CO2.

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Thanks guys! I'll keep them running 24/7, and I think I need to add an additional intake hole.

if you have a co2 coming from a tank rather than just relying on fresh intake air, would leaving the exaust fans off all night be alright so long as temp and humdity stay the same?

Co2 does nothing at lights out. You only need it during lights on.

And just like people, plants need to breath.

Peace

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My Little Grow LST'ing w/Hardware

My Outdoor Odyssey 2008 BONSAI MUMS

My Little Grow Indoor To Outdoor 2009

my fans/intake stays on 24/7