Over-the-island exhaust vent question

msbrandywinevalleyOctober 5, 2013

We're in the throes of designing a new kitchen (actually, a modification/update of the existing kitchen is more accurate). I have vowed to get rid of my totally useless pop-up downdraft exhaust fan and replace it with an overhead exhaust. This is not as simple as it sounds because the island is in the middle of the room and there's a room right above it, so it can't be exhausted straight up and out. In fact, because of how the joists run, it's going to require four separate bends of the ductwork in order to accomplish this.

We'll rely on the advice of an HVAC expert to design an efficient exhaust system, assuming it's even possible. But I'd like to hear from anyone else who has experience with this kind of situation. How large (diameter) does the duct have to be? How powerful does the fan have to be? Should we consider putting the fan on the end of the system, rather than on the end where the hood is? Is such a design even feasible -- that is, after going through considerable expense, will it work efficiently? How can I make an informed decision about this design? Thanks for your input!

This post was edited by msbrandywinevalley on Sat, Oct 5, 13 at 13:38

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We have selected the Miele Decor hood because we won't know until we open up the ceiling and walls if we will be ablel to vent into our building chase vent, or if we will need to recirculate. We also have an island cooktop.

    Bookmark   October 5, 2013 at 6:14PM
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I briefly considered the option of a recirculating hood, but then decided against it. If I can't have an exhaust that goes to the outside, I'll opt for no exhaust at all. In a sense, that's what I have right now, since my downdraft system, which cost as much as my cooktop, is beyond useless.

    Bookmark   October 6, 2013 at 11:47AM
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Our architect has used the hood as recirculating in several clients homes and said they are vey happy with the results. When I asked about a down draft he said he would refuse to install one because they don't work.

    Bookmark   October 6, 2013 at 11:57AM
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I just had a conversation with my kitchen designer who has consulted with his HVAC person. Here's what he told me -- he said that every 90-degree bend adds 5 linear feet of ducting. That means that the 4 bends plus the distance from the hood to the outside will total about 35 linear feet of ducting. He told me that an exhaust fan of 300 to 400 CFM will adequately vent cooking odors and steam. Keeping in mind that this is over an island, does this seem like adequate exhaust ventilation?

    Bookmark   October 7, 2013 at 4:31PM
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