I am installing my OTR microwave. The venting looks like it will definitely not align.
In any case, can I simply use flexible venting to connect the microwave flange to the roof venting?
Also, I need to extend the boot to allow for the damper to close (nobody does this on the YouTube videos). Do I need to create this, or can this be found in stores? I could not find anything like it a Home Depot the other day. I guess I could use a longer boot (say 4" instead of the "required" 3.25").
I would find a boot that covers the cabinet opening and install that, then see where you stand. A bit of flex duct may be a good solution (the semi-rigid kind, not the cheap foil junk), but a side-offset boot may line up perfectly. This one looks like what I have in mind, though the offset may be an illusion:
Image courtesy of Home Depot
Be aware that such a boot should slip over the flange on the microwave, eliminating contact between the exhaust and the wood of the cabinet.
I had the exact same problem. I used a 3.5" x 10" rectangular duct to go up through the cabinet into the attic. In the attic, I used a rectangular to 6" round adapter, then 2 adjustable elbows to get the right offset and angle to line up with the roof vent, and a straight pipe from the elbows to go up through the roof. Bonus... I still have enough space in the cabinet to use it for storage.
I wouldn't recommend flex duct because all the ridges will collect airborne grease being sucked up from the stove.
