Our hood goes right to the ceiling, and I decided I did not want to cut holes in the hood for the fans as the tank/hood can be seen from three sides. So I decided to mount bathroom type vents in my ceiling and duct their output down thru the top of my hood. I went to the Home Depot and they had a bunch of bathroom fans setup in a display. You could turn them on to see what kind of noise levels they produced. I found a nice fan that moves 110CFM and operates at 1.5 sones (sones is a measure of sound that most household fans a rated with). 1.5 sones is VERY quite. They are bit costly as you get to the higher quality, quieter models, but if quiet is what you are looking for, THAT is quiet. I ended up buying them online to save a few bucks, but actually being able to hear what the sones numbers mean made all the difference for me. If you have suspended ceilings and there is clearance above it, you could get a cheaper/louder fan and duct it from another room where noise isn't so much of a factor. In fact, if you do take this route, I have 4 50 CFM fans that I paid $15 each for and am not going to use. I don't know if this will do you any good, but I figured it might help if you go that way.
-Dave
