I have the 36" version. The fan assembly/blower sits inside the pyramid part of the hood. The extension is just a three-sided box of metal to cover the ducting for aesthetic purposes.

Although I haven't looked up the specs, my guess is that you'll need an 8" duct for that hood.

Gtadross - thank you! Just what I needed to hear! That's what I thought too but the pictures on the wiring diagram page had my husband thinking that the fan unit extended above the pyramid piece. We are getting the walls ready for Sheetrock next week and we wanted to be sure of the vent placement.

Willtv- The instructions say 6" duct. We are just getting the 600 CFM. 1200 CFM makes the jump to 10" I think.

khallock, Yep, a 6" duct should work for a 600cfm unit.
Although, it may be more quiet with an 8".
Just something to consider.

Well the 6" elbow and vent on the outside of the house has already been purchased. Not that its a big deal but my husband will not want to change anything at this point. I thought you had to go with whatever the size they tell you that the blower takes? Oh well! This is a DIY kitchen remodel and I wont both DH with these details. I dont expect us to have to use the vent all that much anyways. We've functioned on a useless Jenn-Air downdraft that didnt even pop up for the past 7 years and before that we always had an OTR microwave, so this will be a huge step up!

Its hard to get the wall ready for sheetrock when you dont have the actual hood in front of you yet! And we want to get it right so we dont have to change anything after the fact. But I didnt want to have the hood & range delivered early when we arent ready for them yet. I would like to take advantage of the delivery guys to set this beast into place!