My carpenter recently installed an externally vented, internal motor, cabinet mount Kobe Range hood in a manner that is consistent with the printed instructions, but inconsistent with the FAQ's on Kobe's website. This is frustrating: the FAQ's state that when the duct is attached to the top of the unit but an elbow will be put in so that the transition goes through an external wall (as opposed to straight up through the roof), then the vertical duct should rise 24" above the hood before the elbow directs the exhaust out of home horizontally. Of course, the printed instructions do not say this. Thus, my carpenter put the elbow in a mere 4" above the hood. My question is: will the exhaust capability of the fans be substantially reduced because the elbow is so close to the top of the unit? (I have not had the opportunity to cook under it yet to see how it works).

I do not have 24" above the unit to raise the elbow, but I can pipe the exhaust straight up out the roof over the hood. My carpenter decided to go out the side because he wanted to avoid poking a hole in the roof. That's a fine concern, except I don't want to impair the exhaust capability of my hood for the sake of saving a few bucks on well-done roof install.

I figure I can live with the current install if there is no more than a 10% reduction in exhaust capability. Any comments would be appreciated. Thank you!!!