90° FLAT DUCT CONVERTER: A converting element that can be placed between the start and end points of an air-conditioning system, for connecting a flat duct and an air-conditioning pipe with a circular cross-section. The system can be more easily covered/hidden by using air-conditioning ducts with a rectangular cross-section and the corresponding fittings. it has a smaller "thickness" size compared to the elements of an equivalent "traditional" circular cross-section pipe system, so it can be placed in narrower places (e.g. above false ceilings, behind floor beams) without reducing (narrowing) the useful cross-section. Restrictions used in the ventilation system can result in higher pressure loss and noise from higher air flow. Characteristics of Gonal Fit&Go system elements: An air-technical element equipped with a special rubber seal on the connection surfaces, which can be used to create a system classified in the highest air-tightness class ("D" air-tightness class!). The advantages of this:- Fast and precise fitting;- Can be installed without tools;- Fixed, displacement-proof rubber seal at the factory;- The position of the fittings can be changed / fine-tuned afterwards without deteriorating the sealing efficiency; - It does not require the use of other solutions that improve/increase the airtightness;- A leak-free system can be created by using them;- Lower noise level resulting from air flow;- High energy efficiency.