i dunno where you are, but every grower in the uk (that i know lol) seems to use RVK inline fans, they are powerfull and designed to work in negative pressure ducting, so no worries about that 4 meter duct you have on either end. reasonably quiet to. they come in a range of sizes from 4 in ch upwards, so thres one for every application.

i personally have found them to be easey to set up, reliable, and quiet ( provided some simple steps to elliminate vibration are used ) its not the fan itself that makes the noise its the vibration against whatever you mount it to.

they are available from many places, but this link shows most of the range.

i have the 8inch(i think) version, and its more than enough for my needs 4-8 plants, 1x400w hps
i could probably get away witha smaller one.
http://www.aquaculture-hydroponics.c...ts.aspx?sq=rvk
babystarbud Reviewed by babystarbud on . help me find a centrifugal fan before i can start again i need a bigger better fan i noticed these fans are pricey but seem well worth the investment i just really cant find a good place with a decent price so im looking for help, something in the 465CFM range would be best......:thumbsup: Rating: 5