Ventilation Question

Hello all,
I am nearing finishing my grow room, but I'm hit with the universal grow room problem: ventilation. I have two boxes. Each one is 2x2x4. Both will use hps/mh lights(250w) , which means heat. Additionally I also have a 200cfm sunleaves windtunnel. My goal is to ventilate both boxes with one fan. The dimensions of the 2 boxes added up match my cfm requirement. So how should I do it? Do a y joint and exhaust air simultaneously that way( problem is I might lose exhaust pressure)? Do an inline series (problem is I will add heat from one box to another)? I'm sure others are facing the same issue with having just one good fan...please help a brother out. PS: I'm planning on passive intake and odor is also an issue.
Cheers

Hey Holmes, I'm a newb, but if you're willing to entertain what I've done you may see results. Though I'm not growing in two boxes, I do have a room within a room and needed a clever way of exhausting all the way out without increasing ambient room temps in the outer cell. I purchased insulated ducting (duct sock), which was a pain to wrestle with, but my temps in the outer cell are perfect, as well as the inner room where the initial heat from my cooltube would leech into ambient temps.

I hope that's clear; I'm rambling a bit. By the way, I'd personally go in-line.

Hey thanks for the reply dude! Could you elaborate more on how you ducted? Or some diagrams on how it would work?

I'm sorry I'm not clever enough with pictures, I hope this helps:

I have passive air into outer cell (just 1 six inch vent port to outside)
I have two passive ports (very similar to above) in the inner cell
1 Can Fan carbon filter is at the start of my active extraction line in my inner cell (this would be your first box)
Insulated duct from filter to cooltube (I just run a baby: MH/HPS switchable at 400w)
Insulted duct from cooltube through inner wall to outer cell (your outer cell being 2nd box)
In your sitch, the outer ducting would connect in-line with your 2nd box light
Mine gets hooked straight to a 6" Can Fan (centrifugal)
After your second light, ducting would go outside box (inside if you choose/have room), and then to your fan, which is hopefully extracting outside of room all together.
Again - I am not a seasoned vet, just an observant student. Good luck, and sorry for all the text.

Hey Fykshun, thanks again for your advice bro; greatly appreciated. This leaves with me with one more question. So I have a 200cfm fan. You are saying have a 6" (radius or diameter?) hole for air to be pulled through in the first box. What about the second box? 6" hole again or smaller to account for loss of pressure? Sorry for all the questions, but you are being a great help.
Happy tokes

You could have a T, with the fan in the middle, blowing out, and the 2 other ends going to the top of both of your cabs. For as small as your cabs are, that plus a passive intake system would be all you need. Maybe a clip on oscillating to break up the heat between your light and plants. Don't over think it, ventilation is what it is.

So are you saying a T joint vs a Y joint would work with no insulated ducting? That would be easier, I just wanna make sure that I wont be running into the dreadful temp problems.

What size passive intake holes would I also need on each 2x2x4 box with a "T' joined fan thats 200 cfm?

I've seen V's posts before, and yield to his knowledge. The six inch passive intake in my outer cell was actually a pre-existing breather for a water-heater. I did no math on the intake. My only real input at this point is that my insulated ducting prevented heat leakage through the flimsy ductwork, thereby ceasing the increase in ambient room temps.

Oh - and sorry, the six inches is diameter not circumference.

in my opinion y would be the only way to go. and the fan would have to be an equal distance from each box otherwise it would simply pull air from the nearest opening leaving the other room to heat up. i would also reduce the size of the two lead in pipes so the fan really has to pull through both pipes just to fulfill its airflow needs.

so to be a little clearer say your fan has a 200mm opening i would probably run 2 x100mm ducts from each box then join them together into a 200mm y piece then your fan then 200mm pipe away. if you simply run 200mm all the way i think the intake system would get lazy. in theory it should still pull the same amount of cfm but it would just be more inclined to draw from whichever side had least resistance. does that make sense?