Carbon filter/fan question

Hi,
I'm about to start my first grow in a 4x4x6.5 grow tent and was wondering if a 6' 250 cfm fan will be enough for the 6' carbon filter, I've heard you need a 400 cfm fan for a 6' filter.
I used this cfm calculator http://cheaphydroponics.com/Merchant2/cfmcalc.htm and worked out that I only need 104 cfm to change the air every 1 min. I then I found this website http://botanical.com/hydro/air/calculating_fan_requirements.html which says to add 20% of the cfm to account for the carbon filter, bringing the total cfm to 124.8.

Is this information/calculations correct or should I invest in a bigger fan?

Link to the fan and carbon filter - http://www.ebay.com.au/itm/281096899278?ssPageName=STRK:MEWAX:IT&_trksid=p3984.m1423.l2649

Regards
Bict


EDIT: Would this be better? http://www.ebay.com.au/itm/6-INCH-ODOR-CONTROL-SYSTEM-WITH-CENTRIFUGAL-FAN-CARBON-FILTER-AND-DUCTING-/281009852591?pt=AU_Seed_Starting_Hydroponics&hash=item416d7e10af&_uhb=1

im using a 6" 440 cfm fan with a 6" inlet X 8"w X 24"L with 150oz of premium activated charcoal (its a big filter). now i might also run a fan speed controller and or may route this thru my ac cool tube hood. i havent decided yet. have to do some more testing before i make the final decision.

from what ive read, always go bigger. that way you can turn it down for less power with a fan speed controller. go smaller and you cant get any more power out of it.

thats a booster fan in the ebay link. imo, boosters are garbage. i only use them for fresh air in and fresh air out.

So ditch the 250 cfm fan and go for a 300 -400 one with a speed controller? Or will the 250 suffice?

yes, an actual fan, not a booster fan.

use the booster fan for fresh air intake or exhaust. they work great for it.

I thought the carbon filter attaches to your exhaust fan?

http://www.ebay.com.au/itm/6-INCH-ODOR-CONTROL-SYSTEM-WITH-CENTRIFUGAL-FAN-CARBON-FILTER-AND-DUCTING-/281009852591?pt=AU_Seed_Starting_Hydroponics&hash=item416d7e10af&_uhb=1
Would this be better??

Yes. And yes.

Thank you guys.

you can lount a c/f and fan any way you like.

examples:

duct/tent/duct/fan/duct/carbon filter
duct/tent/duct/fan/carbon filter
carbon filter/duct/tent/duct/fan/duct