I got this extra-wide (42") range hood from a Sears store that sells refurbished appliances. It's dented right in front, but it was cheap, and it has twice the flow rate of a standard unit. There were knock-outs for a standard-sized (10"x3.25") rectangular vent in the top and back. I opted for the top and adapted it to 6" round pipe.
In the next photo, you can see the round pipe running from the hood through the joist bay to the rim joist. I really ought to insulate that pipe.
Here's the vent assembly on the outside of the the house.
To put that in, I had to cut a hole in the side of the house. A friend with a hammer drill came over to help me (thanks, Tom).
Keeping the fan on full blast during the boil keeps condensation and humidity in check. It doesn't completely eliminate the smell of boiling wort in the house, but it's a considerable improvement. I keep the fan on low when working with cooled wort or yeast, thinking the resulting updraft will prevent bacteria-laden dust from landing.