roughing in 3 1/4X10 duct for microwave/fan combo

First I like to thank everyone for helping me with my kitchen remodel. I have yet another question. My stove and microwave will line up between 2 studs. I want to vent the microwave out of the back with a 3 1/4 X10 elbow, up between the 2 studs into the attic where it will go out a roof vent. My queston is should the duct be flush with the sheetrock in the back of the unit or should it stick out a little? How does the unit connct to the duct? The instruction manuals on GE's website are kind of vaque and really does not say how to attach the duct to unit. Thanks again!
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venting, you'll see that it leaves a small projection that fits into the elbow in the wall. However, usually, I think the m/w is vented out the back normally when it is to be vented straight out the wall to the outside. Most of the time, the m/w would be vented straight up into the cupboard above the m/w, where it is converted to round pipe and then straight up through the cupboard, the soffit, and then on up through the attic and out the roof. If you're planning on just venting it into the attic and hoping a roof vent will take care of the added moisture in the attic, I think you'll be disappointed. Might not meet code, also, as it would have the potential to push a stove top fire up into the attic. Furthermore, what did you plan to do about getting that rectangular vent pipe in the wall, through the horizontal 2x4 capping the wall joists. (couldn't remember what you call it, actually). Around, here (Northern Illinois), hoods and m/w hoods are usually ventless because of the loss of heated air and/or infiltration of cold or hot air in the Winter or Summer. Back in the 70's during the first energy crunch, I remember that in Wisconsin, you couldn't get a permit for a gas furnace in new construction if the hood was vented. May not be that way anymore. Sorry for the lengthy post...(my experience was in selling these things from their beginning until my retirement a couple of years ago.
Tom G
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Thanks for the info. I was at Lowes tonite looking at the floor models, and the adapter is about 11/16 long, plus the back of the microwave is flat, so I have no choice but to make my duct fluch with the sheetrock, otherwise the microwave would hit it. I am not venting my fan into the attic. I will be using a roof vent.
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