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I'm replacing the over the range microwave in my house, and the new microwave's exhaust vent does not align with the existing ductwork and hole in the wall for the exhaust - neither vertically nor horizontally. I'm unsure of the best way to solve this issue.

Complicating the issue is that the place where the new hole would be placed is centered on a stud. The left side of the duct is very close to or in contact with the stud.

This is an interior wall. The duct work runs up to the roof of the house.

What are my options here? I'm not sure how I could get the air flowing into the existing ductwork.

enter image description here

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  • Is that the duct going out the back of the wall? Is the MW duct on top? – HoneyDo Dec 7 '20 at 3:49
  • The microwave can be adjusted to have either a rear facing exhaust or top facing exhaust. – you786 Dec 7 '20 at 3:59
  • In the picture, the blue rectangle represents the new microwave's exhaust placement if configured as rear facing. The existing hole is into the ductwork that exits to the roof. Does that answer your question? – you786 Dec 7 '20 at 4:00
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You may need a custom fabricated part in that configuration. Alternatively, how do you feel about the microwave venting vertically? If you sacrifice cabinet space you can use a flexible connector inside the cabinet and may be able to use off the shelf parts

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  • Ahhh, a custom fabricated part? Sounds expensive and/or complicated. I think going into the cabinet might be an acceptable alternative if it's going to be too much to try to use the rear facing exhaust. – you786 Dec 7 '20 at 4:29
  • Would the idea be to cut one hole in the bottom of the cabinet and one in the back of the cabinet into the duct, then use some sort of flexible connector? – you786 Dec 7 '20 at 4:30
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    "Custom Fabricated Part" - a small galvanized steel or aluminum box with a hole on one side that matches the microwave and a hole on the other that matches the wall, the thickness of the space between the back of the microwave and the wall. i.e. a rather simple duct, that any HVAC place worth its salt could whip out without breaking a sweat. – Ecnerwal Dec 7 '20 at 5:25
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    I ended up going with your suggestion of venting vertically through the cabinet space. So far, so good. – you786 Dec 11 '20 at 3:03
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The simple solution is to return the unit that you just purchased. Then using the information that you now have (i.e. the wall duct location) shop for a compatible unit.

There are probably a number of ways to deal with the existing venting but they will entail opening up the wall and installing alternate framing so that you can re-locate the in wall venting. To be honest with you, being as you are asking this question here, the idea of opening the wall may not appeal to you and may very well not be your cup of tea. What this means is that your first option is likely the path for you.

If you do elect to open up the wall do consider if it would be better to open up on the opposite side of this interior wall. This would be especially true if the wall on the other side is much less encumbered with cabinetry and back splash tiles.

A big consideration will have to be made if that interior wall is load bearing or not. Below I show a possible framing change to make to the existing wall from the opposite side. This layout could be used for supporting wall or not.

enter image description here

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  • I actually expected that to be part of the solution (opening the wall and installing new framing) so I'd love to hear a detailed explanation. It's actual the duct work that I'm more concerned about. The framing as far as I can tell seems to be some use of a reciprocating saw and a few 2x4's cut to the right lengths, right? Doesn't seem so bad - but I could definitely be wrong. – you786 Dec 7 '20 at 4:28
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    Changing the framing will be much dependent upon the nature of that interior wall. If it is load bearing then you would have to account for that to make sure the wall above is properly supported. – Michael Karas Dec 7 '20 at 4:38
  • Gotcha. Great idea to use the opposite wall, which like you guessed is just some paneling and drywall rather than tile work. Would the framing be unnecessary if the wall is not load bearing? – you786 Dec 7 '20 at 15:45
  • Do the framing anyway to keep a solid and secure wall. – Michael Karas Dec 7 '20 at 19:33
  • Thanks for the detailed explanation and suggestions. I upvoted this one, but I'm accepting the other answer because it's what I ended up doing - going through the cabinet above and making a hole out the back of the cabinet. – you786 Dec 11 '20 at 3:02

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