Rigid steel duct is required. The meaning of rigid here is that of sheet metal, not cast pipe. The issue is resisting a grease fire in the duct, which corrugated aluminum will not properly resist.

Check with your building inspector on packing around the duct. I would expect fiberglass insulation to be acceptable. Else ceramic insulation, firecode sheetrock, and similar products may be suitable.

You can use any combination of straight and curved ducting you wish, up to tens of feet, with the caveats that the diameter has to be appropriate for the flow rate, and that added length and/or elbows increases pressure loss and thereby reduces the blower's actual performance. In your stated geometry, I expect the elbow loss to be less than the pressure loss across the baffles in the hood.

Not that minimize elbows means use as few as possible, not make them small.

kas

i was writing this on my phone while trotting through home depot! I am shocked you understood my gibberish haha.

We are using the rigid duct. Shockingly enough, the hood came with a flex pipe.

The wall we are punching through is sheet rock, fiberglass insulation, wood clap board siding, finally composite shingle then outside air.

: <at 19 inches = hole punches out to exterior. the duct goes 90' out of it > :

: :

: chimney / duct for 19 inches straight up

: :

: :

_________

<top of fan portion (the big triangle piece) It is 13 inches from bottom baffle to chimney start>

_________________

28 inches

___stove top____

O O O O

The duct is 6 inches - The top fan of the hood is made to receive 6 inch duct so assuming that is the correct diameter.

We will be using the high heat tape to connect the duct together unless there is a better method.

Thank you for all the input. I just wanted to clarify everything in case anyone else had some tidbits of wisdom. HAHA I couldnt figure out how to edit my original post. not very tech savvy :-P

Although there can be occasions when it is "better to ask forgiveness than permission," these don't include interactions with local Code Enforcement. When in doubt, ask. One might view Code Enforcement / Building Inspection as the means for avoiding future expensive legal fees or insurance payout refusals.

The outside duct cap should have enough sheet metal covering the side shingles that the hole in the shingles can be larger than the duct diameter, thereby providing a thermal gap. Check your directions for the recommended hole size.