Question for the aerodynamicists
Installed a commercial upblast fan on my exterior wall.
Fan "throat" is 8" diameter.
Duct from hood is 10"x10".
Stud spacing is 8" (?) so absent more work than I'm willing to do, I need to use a 10"x10" to 8" round reducer to get through the wall.
Q: should I . . .
Choice A: end the 8" duct at the wall exterior, so the air goes from 10"x10" duct to 8" duct to large space between duct and throat to 8" throat?
Choice B: extend the 8" round duct to meet the fan throat, so the air goes from 10"x10" duct to 8" duct to 8" throat?
I was thinking Choice B will have less turbulence, even if the air is confined in the 8" duct for an extra six inches or so compared to Choice A. I was also thinking it might make no practical difference so i should do whatever is easier.