Some grow box Q's

Hey everyone, I'm working on putting together my first grow box and i have some questions concerning air circulation and ventilation. First off, do I need an intake fan or can i just have an exhaust fan? I was thinking with only an exhaust it would pull air through any leaks i might have making sure i can get all the air from my grow room through my scrubber to keep odors to an absolute minimum. Also I was wondering if just a 4 inch inline duct fan will move enough air to keep temps down? What kind of fans or blowers would you recommend? I have been having trouble figuring out computer fans, maybe I'm doing something wrong or maybe the fans are broken. (I pulled them out of really old computers) Thanks Everyone!

You ideally want to exhaust your space with a fan rated to move the volume of air in that space out of there within 3-5 minutes. If your space is 4 x 6 x 8 feet your volume of the room will be 192 cubic feet. In this case you would want a fan rated at a min. 38 - 64 cfm. (divided the volume by time desired to empty space)

As far as intake fans go, you don't necessarily need one. You can use passive system (ie holes) But you should really seal your area as tight as you can to help manage scents. If you decide on a passive system, I believe you will want the size of your intake hole to be twice the area of your active output (the exhaust). If you use a intake fan to help with this, I believe you want your intake fan rated at 80-90% the rating of your exhaust fan. Hope this gets your started.

Thanks flamdrags! I think I'm just gonna go with with an 80cfm duct fan to start out with on my first grow box because i don't plan on having a large grow or grow box

Having a passive intake is fine.

You just need to create negative pressure in the box through your fan/filter and you should be all set.

cool tortoise picture, too

Haha thanks man! I have decided that is what I'm gonna go with unless someone convinces me to do otherwise.
Another question i have is what can i use to fill cracks and really make my box "air tight"? it would be nice if it solved light leaks as well but that can be taken care of later, my first concern is keeping smells to a minimum. I am going to start building tomorrow and I'm aiming to finish it this weekend. (probably wont finish it but I'm gonna try)