Recently, I reworked a Hood Duct exhaust system for a customer. The unlisted 15' Hood provided many constraints and obsticles to properly size the duct. We were able to fit a 8" x 22'' trunkline on top of the Hood with 2 Exhaust risers centered on each side. The ductwork 90'd off the right side of trunkline( to the rear of the Hood), then transitioned to 16" x 16" (with 2 offsets inorder to get through the wall and obsticles) out the building 10' to an Outside Wall curb positioned at 45 degrees. The system passed inspection but needs to draw more CFMs as the Kitchen is very Hot and smokey because of the Radiant Charbroiler.
Also installed was a Front PSP Make Up Air system.
The Upblast fan is 2Hp 4750 CFMs.
I'm thinking about changing the 90 to a radius corner and ending the Trunkline at the end of the Leftside riser( currently the trunkline extends 8-10" beyond the Riser).