Intake/Exhaust Set Up

Ok People,

I've searched and researched the topic but every thread that i read points me back the other direction.
After a week of plannig and getting the items needed I am beginning the build tomorrow.
The box will be 30"L x 18"W x 54"H.

The only question that i have unanswered is this one.

"What would be the best intake exhaust set up for my grow box?"

Out of the researching that i did do i came up with the following options for my setup:

1.) 120 mm, 74 CFM Exhaust Fan - 80 mm, 33 CFM Intake Fan.



or

2.) 120 mm, 74 CFM Exhaust Fan - 8" Passive Intake Hole.





Thanks for the help!

Figure out your cubic feet multiple it by 3 that's your Exaust cfm size needed. u can have a lil more or less. Then for intake find a fan with a lil less cfm then Your Exaust. That will cause negative pressure and u want slight negative pressure.

Cubic ft = length x width x height

A lil more info- the reason u want a cfm 3 times your cubic ft is cuz u want the air changed 3 times per minute in your grow space

Thanks much for the info.

The cubic ft of my box = 16.8. So my CFM needed would be around 50. The exhaust fan i plan on using is 74 CFM, and will be pushing the air through a small carbon filter. Intake is a smaller 33 CFM fan. That setup should put me right around the CFM that i need if my thinking is right. This was my original idea when i first started planning.

Would anyone suggest using the "8" Passive Intake idea" instead of this one? Or any other ideas.

Sounds like your right on the money bro . Uhm what kinda light u using? A passive intake would probably work fine for your set up if u r using hid lights I'd use the intake fan though they run hotter and a fan will pull more cool air in quicker

High temps wont be a issue with my lights.

I'm using 8 - 26w 6500k CFL's for veg, and then switching to 2700k for flowering.

I think i'm still going to go with the Intake fan simply because it will be much easier to trap the light than a 8" hole in my box would be, and i already have the two fans ordered.

I would go w/ the passive intake
here is some good info on venting
https://www.rollitup.org/grow-room-design-setup/406726-all-air-guide-proper-ventilation.html