Ya huge difference in CFM's. I first bought a 4" as a hood exhaust which worked until summer, then I ended up with a 8" which works pretty well for a 600 watt and triple digit summers. The second one as it turns out I also own. I use the second one on a 6" insulated A/C duct as a way to draw in a little more cool air as well as to draw in fresh air for when the A/C is off. I wont tell you it's the most efficient way to go about this, but it works. Huge difference in cooling and air moving capacity in those two fans.

I will also be using something like the second fan on a roof mounted turbine in my garage as well. I'll use it to push all the smoke out of my garage. Since I wont need much to vent second hand smoke, a lower cfm fan should be fine.

You can use the second fan for general light air circulation only. If you need any type of cooling or heat dissipation, then the first fan is what you want. Pay close attention to the size room you have, the amount of heat you have and as a result how large of fan you buy. One size does not fit all.

Also, there is a line of Chinese made vortex fan's on ebay. I have only been using it for about 6 months but it was through 106 temps and it's still running. I mounted it on a bungee cord suspended from my rafters and as such the noise is more apparent at the intake then where the fan is located. Bottom line, some people argue those fans are shit, but at 1/3 the price of the others, I'll go ahead and tell you it's worth the risk.
Prodaytrader Reviewed by Prodaytrader on . Exhaust Fan Where can i find a good exhaust fan for my grow room? Would a, 6 inch INLINE DUCT FAN exhaust BOOSTER blower cool air, work? i found it on ebay lol Rating: 5