Thank you cooksnsews and cat mom. I was stunned at how dirty the exterior of the hood was even though it was wrapped in plastic. DH says he thinks that stainless hoods are shipped with some sort of protective film of, for lack of a better word, "vaseline" over it that needs to be cleaned off and that might have trapped a lot of dust before it was wrapped up. When I wiped the hood down it did seem to that it had that feel of something like that. Of course in all the mess we have right now I can't find the instruction booklet that came with the hood to find out for sure. Right now we are in the final stages of cleaning up trying to get our c.o. so I'll try a better cleaning after we move in. Thanks again.

The vents are for when it's in recirculating mode. They aren't functional otherwise. So, it's a visual thing for you a to whether or not you want the duct cover flipped.

Mine's a Vent-a-hood (Euroline Pro model, EPH18-242-SS) that I bought from a local retailer. I wanted something eye catching yet still simple since there's a lot going on with the tile. It works great, too. I have a 42" hood over a 36" rangetop. Here is a link that might be useful: Vent-A-Hood Euroline Pro

If your hood is on an outside wall, your not going to want to protrude through the roof too close to an overhang, especially if you are in cold country with ice dam concerns.You would have to elbow up to a higher location.In our area,a fire stop is required where the ducting enters the cieling/attic with any framing required to be 2" away from the duct.A fire stop is a sheet metal jack that accepts the ducting in the center.The fire stop is attached in your attic to cieling joists or blocking or both.The fire stop isn't so much for heat,as hoods aren't high heat,but are required to slow fire through penetrations.Your roof sheathing should be cut 2" larger than the ducting as well. The roof jack will easily cover that. A t-top roof jack is simply a jack that has a horizontal "hood" that keeps water out of the jack/ducting. You are going to want to study how other vents on your roof were flashed as well concerning your roofing, as an improper flashed jack is a guaranteed leak.If you use foil tape on the seams of your ducting,(my choice), make sure it is rated for heat.Good luck on your project! You might want to check in with your local yocals for venting requirements in your area. That's what they are there for and is a safer bet.