Im getting ready to install a vent system for a new electric brewery Im constructing. I bought an ActiveAir 6 inline fan and speed control. (one of these http://www.plantlightinghydroponics....an-p-2754.html) Ill have about a 5 straight run from my hood, then a 90 degree turn and about another 2 of venting before it ports outside. I have a nice 4 hole saw, so I was thinking I would cut a 4-inch hole and use a reducer to drop to 4 right at the outlet. Ill be drilling though aluminum siding and I believe there is just one rim joist I have to go through. My question is, being I have to drill a hole either way, am I better off just drilling a 6 hole? Its kind of scary drilling that big of a hole in the side of my house. 6-inch hole saws seem hard to come by and very pricey, which is also why I am hesitant to do this. Im guessing airflow will be pretty good even with the 4 reducer. Ill be brewing mainly 10gallon batches. Any thoughts would be appreciated.