An extractor assembly to be installed inside an air duct, the extractor assembly comprising: - an impeller having a base (1.1) and blades (1.2), the blades (1.2) projecting from the base (1.1); - an actuating element for imparting rotational momentum to the impeller such that it generates an air flow by means of the blades (1.2); - a support having a first face (3.1) and a second face (3.2), the first face (3.1) being for fixed arrangement of the actuating element; - a case comprising a first portion (4.1) and a second portion (4.2) 4ef surrounding the impeller, actuating element and support; wherein the support comprises: - an internal wall (3.3) that determines, with the first face (3.1), a housing for accommodating the actuating element; and - an external wall (3.4), which is disposed radially and externally with respect to the internal wall (3.3), such that these walls (3.3, 3.4) define a passage for the movement of air; and, when the extractor assembly is mounted in a use position, the external wall (3.4) makes radial and internal contact against the first portion (4.1) and the second portion (4.2), as well as against a joining area of the first portion (4.1) and the second portion (4.2) with each other, such that an air outlet along the external wall (3.4) remains blocked, and characterized in that one of the first and second portions (4.1, 4.2) has a step to overlap with a corresponding longitudinal end of the other portion (4.1, 4.2) and the joining area is formed by the overlap between the first portion (4.1) and the second portion (4.2). - an impeller having a base (1.1) and blades (1.2), the blades (1.2) projecting from the base (1.1); - an actuating element for imparting rotational momentum to the impeller such that it generates an air flow by means of the blades (1.2); - a support having a first face (3.1) and a second face (3.2), the first face (3.1) being for fixed arrangement of the actuating element; - a case comprising a first portion (4.1) and a second portion (4.2) 4ef surrounding the impeller, actuating element and support; wherein the support comprises: - an internal wall (3.3) that determines, with the first face (3.1), a housing for accommodating the actuating element; and - an external wall (3.4), which is disposed radially and externally with respect to the internal wall (3.3), such that these walls (3.3, 3.4) define a passage for the movement of air; and, - an internal wall (3.3) that determines, with the first face (3.1), a housing for accommodating the actuating element; and - an external wall (3.4), which is disposed radially and externally with respect to the internal wall (3.3), such that these walls (3.3, 3.4) define a passage for the movement of air; and, when the extractor assembly is mounted in a use position, the external wall (3.4) makes radial and internal contact against the first portion (4.1) and the second portion (4.2), as well as against a joining area of the first portion (4.1) and the second portion (4.2) with each other, such that an air outlet along the external wall (3.4) remains blocked, and characterized in that one of the first and second portions (4.1, 4.2) has a step to overlap with a corresponding longitudinal end of the other portion (4.1, 4.2) and the joining area is formed by the overlap between the first portion (4.1) and the second portion (4.2).