So many vents...some of them can be up to 1500 CFM (CFM is cubic foot per minute or how many cubes of air are filtered in a minute), this does not guarantee proper venting.
Assuming the vent is specified correctly, the following is the best way to duct a hood.
Pardon the non industry terms...
1. Straight up...smoke is headed in that direction. This is the most efficient way to vent.
2. Straight back: Smoke is still going up, but is being redirected through the back of the hood.
3. Straight w/elbow: Right direction for the smoke, but adding an elbow decreases efficiency.
4. Downdraft: If you searched the blog for venting, you will find I am not a huge fan. Proper venting requires capture area, which is non existent in a downdraft...It is however better than nothing and can be useful in an island.
Avoid:
Too many turns/elbows: This decreases efficiency.
Long runs: same as above.