I second the AC Infinity fan! These things are AMAZING, cheap, they move a TON of air, and they're relatively quiet compared to the BUZZ and RATTLE you get with most cheap, stamped galvanized fans. I have a single 12" fan in my 1200 sq/ft print room, and I have mine reduced down to 8" and it moves a LOT more air than just a 6" alone. I found that you kind of NEED a little bit of reduction in the output ducting in order to increase the velocity and get the air to MOVE. Once I put the reducer in, I lit a cig in the area below the intake duct, and the smoke moves up toward the ceiling and when it get's within a foot of the ceiling it's quickly sucked toward the intake grill and out of the room!
I also bought a couple cheap electric dampers, and hooked them up to the intake side with a Wye adapter, and I have the first run going to a ceiling grill above the printer, and the second run comes out the ceiling via flex duct and runs directly into my Laser Cutter cabinet.
I can run the fan on full speed with both dampers open, and it still clears all the smoke out of my laser cabinet, but most of the time I only run with 1 damper open (above the printer) and the laser damper closed off, to help increase the suction in ceiling intake. I have both dampers hooked up to a cheap doorbell transformer and wired into a low voltage swtich box with a couple of toggle switches mounted in it (one for each damper).
As long as no one accidentally closes both dampers, it works GREAT!
AC Infinity ALL THE WAY! (Go with the 8 or 10" and reduce it down to 6" as close to your external wall as possible).
Keep in mind you can easily control the fan speed with the included controller, so I would go with the bigger fan, and you can always slow it down if it's too much (which it won't be).
a side note, after installing the AC Infinity at my shop, I went on amazon and bought 2 more of them (another 8" and a 10") and installed them in my HOME because I was THAT impressed at the build quality and performance. One in my bathroom (with the optional "muffler" to make it quieter), and the second one in my attic with their optional smart controller that automatically spools up the fan if the temperature or humidity level hits my pre-set point, my attic has never been drier, and it helps keep the house cool in summer by sucking the HEAT out of the attic space!
A tip, to reduce the noise, remember to install it by suspending it from a ceiling joist with cord/rope, and to reduce the "jet engine" sound of all that air moving, remember to keep your duct runs as straight and smooth as possible! Don't use ribbed flex duct, use smooth galvanized if you can, and mount the fan away from your ceiling intake grate if you can. I mounted the shop fan in another room, so the only sound I hear is the air moving through the ceiling grate, it's not a "fan" noise, it's more of a continuous "whisssshhhhhhhh" sound, like a commercial AC duct sounds when it's blowing.
I LOVE LOVE LOVE this product!
Good luck!
