Poor duct design and incorrect or ill-fitting ducting are the leading cause of venting inefficiencies in rangehoods. And when that happens, all the extraction power in the world isn’t really going to help. Not to mention the pollutant build-up over time that may lead to costly maintenance and safety issues.
The Schweigen Isodrive® system is externally-mounted, and works by pulling air through acoustically-matched flexible ducting. This results in high-flow extraction that is virtually silent at the rangehood. The use of a rigid ducting system here would have an organ piping effect - similar to a didgeridoo, where noise produced at one end of a hollow rigid pipe is amplified out the other.
This is why all Schweigen silent rangehoods come with quality, right-sized flexi-ducting at no extra cost.