Pipe size for vent in over the cooktop microwave
I have a microwave that’s mounted over the cooktop. It has a built in range hood that can be ducted to the outside. I need to avoid a stud to get the vent outside, so I’ll have to convert from the 3-1/4 X 10 outlet to round pipe and make a 90 to go through the wall. The directions for the microwave say to convert from 3-1/4 x 10 to 6” round.
I have a really nice 5” vent that’s left over from a Jenn Air downdraft cooktop that I’d like to use so I can make smaller holes in the wall and take up less space in the cabinet above. The total run is probably less than a foot. It’s basically up a couple of inches from the top of the microwave, a left turn, then out through the wall.
Is going from 3-1/4 x 10 to 5” round too much reduction given the shortness of the run?