Choosing an exhaust hood -- where to begin?

msbrandywinevalleyOctober 7, 2013

We're in the design stage of a kitchen remodeling project. I'll be keeping my Dacor gas cooktop, but ditching the useless Dacor downdraft, which we hope to replace with an overhead exhaust hood.

But this is not without its challenges. The cooktop is in a peninsula and a straight-up exhaust system is not possible because there's a room directly above. We'd like to go up, through the ceiling and out, but the joists change direction before we can go up and out. After consulting with an HVAC person, my kitchen designer has suggested coming down into a transom, going across below the joist and then going up and out. That means a total of 4 bends in the duct. He tells me that every 90-degree bend adds 5 linear feet of ducting. If that's correct, I'll have a total of 35 linear feet of ducting.

Another piece of information -- my gas cooktop has 4 burners. It's 30" wide and has a total of 46,500 BTUs.

So my questions are: Is overhead venting feasible, given the constraints? And, if it is, what size (width) overhead hood should I get, and what CFM fan? Also, is there a reason for me to consider a fan on the outside at the end of the duct, rather than at the hood? (I apologize if my terminology isn't correct -- this is new territory for me.) Are there certain brands of vent hoods I should NOT consider? I don't have an unlimited budget, but I don't want a piece of junk.

Any guidance that anyone can provide will be greatly appreciated. Thanks!

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kaseki

Heh heh heh. This topic can be as complex as you are willing to tolerate. If you have the time, I have the material. Visit my My Clippings for links to relevant references that will provide background information. Review the near endless threads on this forum related to this subject.

I don't have the time right now to repeat this material, but one key fact you need to internalize is that there are more restrictions to flow rate than just the feet of ducting, and these reduce the actual flow rate. So once an effective flow rate is determined sufficient to capture and contain the effluent over the aperture area of the hood, it should be scaled up by some factor (such as 1.5) to specify the zero-static pressure capability of the fan.

kas

    Bookmark   October 7, 2013 at 8:08PM
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