The original post: /r/diy by /u/ElbowSkinCellarWall on 2024-12-22 23:54:38.

I’m replacing a dying over-the-range microwave with a new one, and I thought that while I have the area open I might install a duct to vent the microwave outside. (The current microwave vent recirculates back into the kitchen, no external duct/vent present).

The duct would have to go straight upwards about 20 inches, then turn 90 degrees to the left and run 54 inches (through 2 cabinet walls), before venting through a rear cabinet wall and a brick exterior wall.

1. Are there any rookie pitfalls I should avoid in terms of efficiency in the air path/air pressure, etc? Best practices for duct size and the ratio of vertical vs. horizontal (if that matters)?
2. Does starting vertically from the microwave result in oils/moisture dripping back into the microwave vent? Should there be some equivalent of a u-bend/s-bend near the start of the duct path?
3. If running the duct along the wall ends up terminating at a stud on the “exit” wall, can I make a little turn to get around the stud, or is it best to run a straight path to the exit point even if that means occupying more of our precious cabinet space?

Anything else I need to consider that a first-timer may not anticipate?

Thanks!