Here is the duct run. It is in a false ceiling of the side stairwell, and is pretty short. There is a 12”x10”xI forget” box above the hood with a 12” (?) collar that fits on the hood outlet, a 90 deg elbow 10”x10” comes out the side of that box (visible in the pic), a 35” straight run 10”x10” to the exterior wall, the 10”x10” to 8” round reducer, then about a foot of 8” round that goes to the 8” fan throat. The Captive Aire guy calculated the pressure drop and selected the fan. He didn’t know about the reducer, because I didn’t know about it then. Hopefully it will all still work.