i'm setting up a homebox xs (2' x 2' x 4') pretty soon and i have all the parts ready except for the exhaust fan. for the light, i plan on having a 250 watt hps housed in a cooltube. i do plan on using a carbon filter...and probably will do carbon filter --> cooltube --> exhaust fan. i know that carbon filters often half the cfm of inline fans. would i be alright with a 4" inline fan at 170 cfm or do i need a 6" inline at 480ish cfm?
i would go with the 6inch, its always better to over do it on you ventilation, then not get a big enough fan, and have to go spend more to get another one....i made that mistake of getting a 4 inch and should have gotten a 6 inch.
mind that a lot of times fans rate the CFM on BOOSED air, not FREE air. so a "250 CFM" fan is actully a 170cfm fan that can keep up with a maximum 250 CFM boosted airflow.
170CFM is plenty for a 250W cooltube. Instead of worrying about a bigger fan, I would be chaning the setup of your filter. Putting the filter behind the cooltube is an awefully bad idea, you'll get no filtration of the smelly air created by your plants! Consider 3 fans, one exhaust with the CF, another intake (could be passive), and your cooltube fan.
i think you may have misunderstood my original post. its going to be..... passive intake--> plants --> carbon filter --> cooltube --> exhaust fan --> outside of cab the fan will be blowing air out of the cabinet...there are passive intakes on the bottom of the cab
It is better to blow cold air throutgh a cool tube as the Fan will move more cold Air than hot as hot Air is less Dence than cold and be mutch more efficient for you there. This means that you can have a less powerfull fan to do the same job. I would make the cool tube a sealed system so no filtering is needed. This way you will only need a small carbon filter and fan for the rest of the room to rid of any smells and bring in your co2 that is mutch needed and I would just run with a passive Air in so still only 2 fans needed. Hope this helps you out there. Best of luck