Exhaust Fan Conundrum

ok, i have a 250cfm duct fan which works fine on its own. the problem is that my exhaust flanges are 4 inches in diameter, causing me to use a 6inch to 4 inch reducer. this causes a rather large amount of back-pressure making the fan expel air from both ends, instead of moving air from one end out the other. so far i have come up with 2 possible solutions, 1: buy a 6 inch flange for my HydroHut and cut new holes to accept it or 2: buy a 4 inch duct fan which is only rated at 80 cfm.

maybe i'm missing something here, but i don't really want to have to cut my HydroHut if it's not absolutely necessary. i have a 6 inch diameter cooltube, so even if i went with a 4 inch duct fan, i would still need a reducer, placing me right back in the same boat. does anyone have any suggestions?

180 cfm Eco Plus 4" Squirrel Cage Blower Fan / Dayton - (eBay item 200147830585 end time Sep-07-07 07:48:26 PDT)
toss out the inline fan and hook this up to your cool tube and scrubber

do you think that will be able to pull enough air through the entire duct layout to keep it cool?

those fans push and pull really well. and i dont know if its a possibility for you but you can find fans like that at places like flea markets or hardware stores cheap. i got a 1000CFM made for home A/C units for just under 150.00 new. its enough to pull air in threw 12' of intake. (2x6" lines) then push it out of 5' of exhaust. (2x6' lines)

nice. maybe i should be paying closer attention to the classifieds and such

New Portable 3 speed Industrial Floor Blower Dryer Fan - (eBay item 120156363720 end time Sep-03-07 21:30:14 PDT)
i have a friend with a room about the size of yours and this is what he uses, but it takes alil DYIing

3 SPEED SQUIRREL CAGE BLOWER FAN EXHAUST FURNACE HPS MH - (eBay item 290156668711 end time Sep-08-07 14:45:40 PDT)
thats almost exactly what im useing to in my room for 2x1000watt lights and a home made air scrubber made from a 5 gallon bucket.

wow! that's some serious air movement! thanks for all of your help