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 4-Zero fire-rated flexi-ducting at no extra cost. These perform optimally at their issued lengths and deliver quality performance at up to 3x that - when connected to an Isodrive® motor system.
Good design practice would always see a fire-rated ducting system extend to the house exterior, rather than to the ceiling cavity. When a rangehood is ducted only into the ceiling space, the collection of humidity and grease can present very real health issues and fire hazards. Over time, the back pressure will also impact the longevity and performance of the rangehood motor.
Different Australian states have varying legislative requirements for the installation of rangehood ducting. Some will insist on ducting being vented externally (i.e. not in to the ceiling cavity); others will not. It is imperative that you check with your state building authority and/or private certifier to confirm their position.