One would have expected Prestige to provide some advice, but without it, I recommend you match six-inch vents with six-inch ducts. Larger ducting reduces resistance but also slows down the air velocity. Commercial ducting requires 2000 ft per min air velocity to limit the amount of grease that will condense. According to some sources I've read, residential velocities should aim for the 1000 to 2000 ft per min range. The two six-inch vents can be merged into a duct with the same cross-section, around 8-inches, but only if both power packs are powered at the same time. Otherwise, keeping the velocity up requires individual ducts. A call to Prestige may be desirable. kas

advisor - maybe we just are reading this differently: "contractor is saying we can run 10 inch off the hood and then "choke it back" to the 8 inch for the majority of the run. " You see , only an idiot would got to the trouble to install an 8" to 10" transition at the hood and then immediately add another one going in the opposite direction to go back down to 8". So what is likely happening is there is the takeoff at the hood at whatever size to 10" for a run of between 2 and 24 feet at which point there is to be another reducer of 10" down to 8" for the rest of the run - or majority as o.p. says. This leaves a big belly in the middle of the assembly. If you think this is good design then you are certainly entitled to your opinion, but fancy website aside I say you're wrong. You are correct about the transitions 8" to 10" is quite common , you can get one of the shelf at your local home depot, and VAH will even sell you one. They'll even sell you one of their wacky 8" plus 6" dual takeoff to 10" round if you get one of their larger hoods. BUT, I'm not letting any contractor go from 8" to 10" back down to 8" again in our projects. You can do what you want, and I'd suggest mrd gets someone that knows what they are doing locally to advise him/her because 1. neither you or I are on site to see what's actually going on, 2. have not been engaged to design the system, 3. seems that the onsite HVAC guy is not quite on the top of his game based on the quoted gameplan. RE: the 600 cfm, might be enough, but what if it's actually not in this case. Are you going to pay for the swap, refund the consult fee, ect.??? I know 900 + will work because it there is a lot of xtra headroom built in. It might cost more, or maybe not as VAH is proud of their hoods, but that cushion is nice. You also do not mention how loud that VAH is going to be especially on full tilt ! May not be important to mrd as (s)he didn't mention it - but what if it is???? Doesn't seem prudent to make a rec to a stranger that is too conservative - but hey it's a free country.

"I may have answered my own question. It seems the max. horizontal run after the loop vent is 6 ft for a 2 in pipe. Does this sound about right?" No. It doesn't sound right. There should be no limit at all for the length of a horizontal run or 'foot vent' that gets connected to a main stack. The only limit in most cases would be on the horizontal length of the trap arm between the sink trap and the island vent itself...which is limited to 8 feet for 2" pipe. See the links below for how Code compliant Island vents should be installed under most codes: http://www.plumbinghelp.ca/images2/Island%20loop%20vent.jpg http://www.terrylove.com/images/island_vent.gif If your kitchen island vent doesn't look like the above diagrams, you're not installing the island vent properly.

Well, Deedles, I'm with you. I love vintage stuff too. In fact, I was actually hoping to come upon a red Chambers stove after my vintage Smoothtop range died in the middle of my kitchen reno. (Not finding one, I ended up with the red Aga 6-4 instead.) Red is definitely not a neutral color though. Most folk either love it or hate it. In my book, this red range and fridge are super!