Has the ducting been installed? If the roof isn't in and trusses aren't installed, then I don't see a big deal in asking for the change. That being said, I installed a Kobe Range hood with (I think) 1200 CFM rating in an 8" duct. It works fine. I cannot remember what the max flow rating is on 7" duct. Have you already picked out a hood? Do you know what the duct size mount on the actual hood is, because that is as big a duct as you should run. I.E., if the hood has an 8" diameter output, going to a 12 inch diameter duct is not going to help as the 8 inch hole becomes limiting.

Be aware that if you're talking about serious air movement volume -- like the 1200 CFM reel time mentioned -- you're going to have to consider provision for make-up air.

The answer is: do it up front. Else you'll have to probably rip out walls and such to pull the 7" duct out and put a 10" duct in.

Thanks for all your replies. The house has not broken ground, so I have some time to decide. When I installed my parents's range hood, I was limited by their house's 7"-diameter duct. I don't want to run into this problem with my house.

I am planing to install a unit with approximately 1000-1200 CFM. Hopefully, this will eliminate almost all of the odor. The Kobe that I came across on here looks promising. I put a Zephyr in my parents's kitchen, so I have experience with that brand.

Like weedmeister says, I am leaning toward doing it up front. I just wonder about cost. I think the builder is going to charge a few thousands for this.

A few thousands??? to run a larger duct? If that is the case, do it yourself, or get a new builder.

Thousands?!? The difference in the cost of the material is minimal and the labor is the same. You're being ripped off!

Concur with weissman. Material cost difference is small

I almost feel the same way as weissman. I don't like the money they charge for JUST obtaining a quote. That bothers me a little bit. It seems like a pretty simple question from the superintendent to the contractor. I could install the duct myself if the builder let me, but that is out of the question for liability matters. I just don't know how much it will cost and would want to avoid a costly remodeling later on after the house is built. My goal is to be able to maximize the CFM and remove all the fume/smoke/smell.

The $150 cost just to ask a question really discourages upgrades, doesn't it? ;)

I would do it now. It shouldn't cost that much extra for a larger duct. A while back when talking to a potential HVAC contractor, I wasn't sure which hood, and therefore duct size, I was going to choose. I asked a question about the cost difference in duct size. They said it was about the same if I went 6" or 8" so I shouldn't base my hood choice on the duct cost.

If there's no re-design work to be done (and writing "10"" doesn't count), "thousands" seems pretty darn steep. Some extra materials cost, sure, but not thousands. I'd ask why. But if you're looking at 1000-1200 cfm units, it's likely better and less expensive to start with 10" than to try to upgrade later.

Is this a house being done by a builder in a subdivision of many homes (more than one)? If so, then I could see why he would want to discourage you from changing from the 'standard' plans. When he's building 'many' homes it is much simpler for him to order hundreds of feet of 7" duct than it is to order both a bunch of 7" and a few feet of 10" for you.

Actually, you should buy the 10" ducting yourself and hand it to the builder with a check for $150 for the change order. I'm only half joking.

10" is probably overkill. But one thing not to overlook is the vent that is being put on the roof or out the wall. I recently installed a Kobe hood which pushes over twice the air of the builders grade hood. This was going up a 5" duct and out of a roof jack that tapered at the top. I replaced the 5" duct with 6" (the biggest that would fit) but the air flow only partially improved. I had to call a roofer to replace the roof jack with a larger 'air hawk' and that really improved the air flow.