It is disclosed a connecting device for the manufacture of ducts for heating, conditioning, ventilation comprising a plate-like element (2) which is provided, on a face (2a) thereof at opposite positions, with at least two hooking points (3) adapted to penetrate contiguous portions to be joined of a duct (4) segment or of two consecutive duct segments. Also provided is a connecting process comprising a step of applying at least one connecting device (19 on either side of a junction line (4a) defined by two opposite longitudinal bands of a panel (5) adapted to form a duct (4) segment.