Conventional wisdom is double diameter for passive intakes.
That's not very accurate... maybe you knew what I meant.

"Double the number of ports" (same diameter) is the recommendation. Looks like your exhaust is actually 3" (with a 4" pickup). So, 2 x 3" intakes, minimum. More is better, if you can keep the light out.

Plan looks do-able; now's the time to test it for ventilation, temps, and light leaks, before you get all green in there. Good luck! :thumbsup:
DreadedHermie Reviewed by DreadedHermie on . Input needed Ok, so let me preface this by saying I live in an urbanized desert, where the temps can be unstable and typically high(even with A/C), as well as avg humidity <20%. Also the components I've listed in the pic are what I already have. I'm trying to make it work with what's available, as I'm on a limited budget, so please don't start recommending something unnecessarily too expensive for this sized grow like a 400w cooled HPS with a 6" vortex fan. I'm trying to rework the ventilation system Rating: 5