Normal or exhast fans used?

Guys just wondering what type and where you got your exhast fan? Im using a fan i got at a store atm and this whole set up a DIY carbon filter things is shitting me.. Ive read all the tutorials on the site but i think i may have a wrong type of fan or set up. Any tips?

imo rhino carbon filters are the best ive tried. tried phat filters and mountain fresh. if youre in uk/europe. i use these for all my supplies.(as there one round the corner) there a good solid hydro store. but like most . you can find the same product cheaper if you look around. but here is the link
http://www.hydroponica.biz/airflow.html

I've made 1 of those DYI carbon filters, had a 250cfm 6" inline exhaust fan & w/ only 1 wrap, vented outside, didn't take smell away. Read you need to use a 80 - 140cfm or the air moves to fast threw the carbon filter to clean the air, switched to a 4" inline 80cfm exhaust fan & double wrap of carbon filter. So far so good no smell at all.