Microwave Exhaust to Exterior from Interior Wall?

Will be doing a kitchen remodel soon and was thinking of venting new microwave to the exterior. However, it will be located on an interior wall perpendicular to the exterior wall. The 12x12" existing kitchen soffit will remain. Was thinking I could run the rectangular ductwork up through the cabinet above the microwave and into the soffit leading to the exterior wall. Seems like this would be easier than opening the wall, but I'm not sure it would even be possible to run ridgid ductwork that distance through the soffit and be able to make connections, etc. And I'm not certain the 90 degree turn would be possible. Might be twisted. (I'm under the impresson that round flex piping is not appropriate for such vents.) Thoughts? Suggestions?

 

7" round is the norm. You might be able to get by with 6" round depending on the length of run.

A typical installation:

- Rotate blower to vent up
- Use included 3.25 x 10 damper. Connect to a 3.25 x 10 x 7" round adapter.
- From ceiling or top of cabinet, run 7" round out wall.

It helps if the cabinet above the microwave is about 24" high. This gives room for the transition piece.
If short, like 15 or 12" high, it can be tough to get a transition in the space.

 

Thanks. Flex pipe or rigid? Wouldn't think rigid could be fed up into soffit above cabinet.

 

Rigid duct. Feeding it up, or running it, will involve removing the soffit drywall and maybe some horizontal supports.

It's worth the extra effort to get a solid run to the exterior.