A nozzle (10) for contact-free treatment of a running web, having a main frame (11) forming an outer part of the nozzle, and two side chambers (14, 15) on each of the longitudinal sides of the nozzle (10). The side chambers having openings (17A, 17B, 16A, 16B) for the air to blow toward a fiber web. A U-shaped air channel (20), through which the air is lead to the side chambers (14, 15), located between the side chambers (14, 15), having at least one opening (19, 18) on each side wall for leading the air into the side chambers (14, 15). A U-shaped inner part (13) which is movable by a mechanism (12) comprising a screw (21) and bushings (22) to at least partially open and close the opening (18, 19).