I used 8" round duct when we installed our wave-solder machine. The fan enclosure is mounted on the wall at the rear of our building - right next to where the exhaust exits the building. The fan enclosure uses a pair of 10" or so diameter fans removed from old DEC racks. The 2 fans are in series with each other - I seemed to get better draw when I added the 2nd fan. Those fans move a LOT of air. As a point of interest, I also added a fume hood on the other wall of the little room containing our wave-solder machine. In other words, the wave-solder machine is flat against the west wall of the little room. I extended the ducting across the room to a fume hood on the east wall of that same room. Dampers in the duct allow one or the other to be selected. The fume hood is great when we are applying conformal coating to PCBs and such. Hope this helps. dwayne PS - I *think* that our machine has a similar 4" outlet. We capped it off - our exhaust is instead taken from the end of the machine where the boards exit the solder wave. We built an enclosure that sits over the end of the conveyor rails and is sealed to the end of the machine (its flush with the top of the machine). The exhaust comes from the top of that enclosure. Both that and the fume hood work well - barely any smell of flux in the room while wave-soldering, no smell of solvents when using the fume hood. No smells of any sort outside the wave-solder room. dwayne At 10:21 PM 1/23/2008, Forrest Christian wrote: >So, I'm putting in (finally) a new-to-me wave solder machine. It has a >4" duct attachment, and the manual indicates that some sort of exhaust >fan capable of 400CFM needs to be attached. -- Dwayne Reid Trinity Electronics Systems Ltd Edmonton, AB, CANADA (780) 489-3199 voice (780) 487-6397 fax www.trinity-electronics.com Custom Electronics Design and Manufacturing -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist