That is irresponsible of your builder and is a warning sign about their knowledge, quality and integrity. Reduction from 8" to 6" alone is a problem. It will reduce air flow and so the effectiveness of your hood and it will increase hood noise as well as the amount of electricity used. So increased cost, more noise, less odor, gas combustion by-products and other effluent removal. Flex duct creates two problems; It's a major fire hazard and it increases static pressure (reduces air flow). From a static pressure standpoint 6" flex is roughly the same as 4" rigid in most installations. At a MINIMUM you should have 8" rigid for your entire run if that is what your hood calls for (Many US hoods undersize this). If you have many bends then you should increase that to 10" to keep static pressure down.

>>It's interesting that there's crown molding on the columns and a lot of detail on the wall, but no crown in the kitchen. Is there crown molding elsewhere in the house?Oh my, have you hit on a sore subject. Crown molding was only included in the formal areas and master bedroom. They also crowned no sloped ceilings. Adding crown to other areas was $250 per "room". $250 now, not so much. 20yrs ago when we're building a house and running out out money, it was. Crowning just that hallway and the adjoining family room cost $500 because it counted as 2 "rooms" even though it was only as much crown as a bedroom; the exterior wall is sloped so the family room is really only 1/2 crowned (one wall not crowned and open on one side). I didn't crown the kitchen because the only wall that would have received crown is that single wall (because again, the outside wall is sloped), and it would have cost me $250. Don't think so. I did the crown in my office myself (come on -- a box) along with the sloped ceilings in the formal living room. If *I* can do it, why in the heck couldn't a carpenter? New cabinets will go up to the ceiling in the kitchen. They put tile crown where I cared in the master bath when it was remodeled. What I should have done was made them crown the hallway to the bedrooms just to punish them. It has so many compound angles it would make any carpenter cry.

I want to echo Weed's caution about being sure on code compliance when having your vent going out near that window. Last year, when I was doing a re-routed of the vent on my range hood, the local building inspector happened by. (We are on pretty good terms so there was no compliance issue.) I asked him about the rules and got a long dissertation as he handed vent tubing up to me. The gist of it was that the rules for range hood vents are different than for those that directly vent gas appliances (say a water heater power vent). There is some discretion when it comes to venting from a range hood over a gas stove. How far the vent has to be from an opening window also varies with whether the vent is above the opening window, at window level or below window level. I was told the vent that is above an opening window can be closer than one at or below window level. BUT, you want to be sure that, if you open the window while the hood is running, it won't be sucking in the vaporous stuff that was just blown out the vent.

We have a 36" 6-burner Bluestar with a 600cfm 42" wide 24" deep VAH over it. Our duct goes straight up and out of the roof of our 1-story home. I hightly recommend that you go with the 27" deep model. Whenever we use the front burners, some of the steam escapes the front of the hood, even when the hood is on high and it's the only burner being used. The 24" hood exterior does cover the burners completely, but the thing is, the front 3-4" of the inside of the hood is a ledge that houses the lights and controls. The steam bounces off of that ledge and some escapes. If I had to guess, probably ~15% of the steam escapes. With the 27" deep model, the control ledge would be beyond the front burners, and that bouncing off of vapors would probably be eliminated or at least greatly reduced. A 900 cfm hood that's only 24" may correct the problem too, but I couldn't be sure. It's just I can literally SEE the vapors hit that control ledge and be deflected out of the hood.