island cooktop hood ducting question


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Old 11-21-07, 03:05 PM
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island cooktop hood ducting question

We are remodeling the kitchen and are planning how to route the ductwork for the island cooktop hood. We know where the island is located and have also purchased a hood with a CFM based on the size of the cooktop (1000 CFM). Directly above the center of the cooktop is a floor joist from the floor above. The floor joists are 2x8 (shrunk to 7 1/4) and are 16" oc.
The range hood uses an 8" round duct, but can transition to 3 1/4" x 12". I would like to run the 3 1/4" x 12" duct in between the joists.

So, my questions are;
How can I run the ductwork without moving the island (the layout is such that the island can move, but it is not preferable)? Do I need to reframe the joists above? Reframing the joists can get the ductwork in, but then this framing would have to be cut to accomodate the 3 1/4" x 12" ducting and would essentially diminish the strength of the framing (see the dilemma?). I can move the joists above, but that would be a lot of work. So much work that it prompted a DIY.com question.
Lastly, where do I find an 8" round to 3 1/4 "x 12" adapter? Would such an adapter fit into the area of the 16" oc x 7 1/4" deep? Would such an adapter have to be custom made? As I mentioned, I could move the island, but the location is limited and would result in an adapter that may not be 'normal/typical' since a 'normal' one might not fit.

I have bought the hood, but did not take delivery yet. I was thinking that I probably should just pick up the hood and get a better idea as to what the fittings need to be.

Any help would be appreciated.
And Happy Thanksgiving.
 
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Old 11-23-07, 04:07 AM
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No replies, your question is not easily answered and probably not to your satisfaction. Locating the hood exactly where it needs to be may not be easy You can modify your ceiling joists, but as you pointed out, not easily. You don't want to compromise the structural integrity of the framing, and certainly not a basic DIY job, unless you have better than average knowledge and skills. 3 1/2 x10 is a common size, and it should work with that. Adapters are usually available at plumbing/heating suppliers. But consider using an oval duct, it might fit better, and big box might have the needed fittings.
 
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Old 11-24-07, 07:40 AM
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Thanks for the info. I am working with a framer that could do the major reframing, but I like to 'think smart' on this stuff and explore other alternatives if there are any. I have a fairly good working knowledge of these things, but I am not an expert and I like to solicit advice from the 'experts' as they may have some 'tricks'.
Thanks again.
 
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Old 11-24-07, 07:55 AM
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I think it is time to bring in a real tin knocker (sheet metal worker). I have seem them do miraculous things with tin.

I would suggest the possibility of splitting the run into 2 ducts run on either side of the in the way floor joist or another possibility would be to make an offset that would run the exit from the hood to one or the other joist spaces above. any competent tin knocker would be able to make this for you. I don;t know how the duct would be concealed in your installation but if needed, the knocker could even make a cover piece that would not show the offset so it would look like a conventional install.
 
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Old 11-27-07, 06:29 AM
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Thanks Nap. I will be looking for a tin knocker today. I agree - the adapter that I need is probably a custom one. I am sure a tin knocker could make something easily.

We have shifted the island plan so that the 8 inch duct can be put into one of the joist bays. The 8 inch duct will be to one side of the bay against one of the joists and hence the need for the 'special' adapter to a 3 1/2 x 12 in square duct. I think splitting the ductwork is too complicated, but I will leave that to the tin worker.

Hopefully, I can find someone in the area within a couple of days.
Thanks again.
 
 

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