Intake and exhaust with CO2

I am about to make my grow room airtight so I can use CO2. The lights (2 600W HPS) I'm using will be aircooled with less than 10 feet of venting from start to finish. I assume its best to have the pressure in the room be a little bit positive so that I don't suck the CO2 out through any leaks in the lights/ducting. Am I better off using two smaller fans (one for intake and one slightly smaller for exhaust) or just one big intake fan? Is this: http://www.plantlightinghydroponics.com/valueline-inch-435-cfm-centrifugal-inline-fan-p-2260.html way more cfm than I need?

...hey man, I just went through the same shit your upto. I made an airtight room, got a double hose a/c unit. The airtight room was made of panda poly. The a/c unit was making the walls cave in due to negative pressure <<< that was the first problem. So, I reenforced my walls with trim wood. 2nd , the humidity was a problem from hell....you'll need a kickass dehumidifier. 3rd, I raised my temps to upper 80's as they say to do.....which I think is a bad idea. My buds ended up waaaay too fluffy (which I blame on the heat).

...when it was all said and done, the bud was totally different...fluffy as hell, non-sticky...different.

...what I'm doing now is: I'm running a room inside of a room ( like a tent), freash air coming in at the bottom of my flower room....while my co2 burner sets outside of my flower room. My co2 statys around 1200ppm like this in the flower room. idk if that helps with anything, but...I was pissed to realize that co2 is more complicated then I first thought.


...only run your co2 while the lights are on, and I wouldn't use a sulpher burner unless you see powerdy mildew...sulpher can change the taste of your buds too. Good luck.