Assembly comprising: - an extraction system, and - a hob with burners disposed in a first lateral portion and in a second lateral portion of the hob, wherein said extraction system comprises: - a main duct provided with an extraction fan actuated by an electric motor, - a first extraction branch and a second extraction branch connected to said main duct, wherein the first extraction branch serves the first portion of the hob and the second extraction branch serves the second portion of the hob, - a mobile deflector disposed in a connection point, - an actuator suitable for moving said deflector, - an electronic control unit operatively connected to the actuator of the deflector to control a movement of the deflector, and - detection means operatively connected to the electronic control unit and suitable for detecting a state of the burners respectively in correspondence of the first portion and of the second portion of the hob, wherein said extraction branches (20, 30) are mounted under the hob and lead to a first grille and a second grille respectively disposed near the first portion and and near the second portion of the hob, the main duct is mounted under said extraction branches (20, 30), the detection means are disposed in said hob, characterised in that said mobile deflector is disposed in said connection point which is between the main duct and the extraction branches (20, 30), in such a way to be: in a first position, wherein the communication between the main duct and the two extraction branches (20, 30) is enabled; a second position, wherein the communication between the main duct and the first extraction branch is enabled; a third position, wherein the communication between the main duct and the second extraction duct is enabled, - an extraction system, and - a hob with burners disposed in a first lateral portion and in a second lateral portion of the hob, wherein said extraction system comprises: - a main duct provided with an extraction fan actuated by an electric motor, - a first extraction branch and a second extraction branch connected to said main duct, wherein the first extraction branch serves the first portion of the hob and the second extraction branch serves the second portion of the hob, - a mobile deflector disposed in a connection point, - an actuator suitable for moving said deflector, - an electronic control unit operatively connected to the actuator of the deflector to control a movement of the deflector, and - detection means operatively connected to the electronic control unit and suitable for detecting a state of the burners respectively in correspondence of the first portion and of the second portion of the hob, - a main duct provided with an extraction fan actuated by an electric motor, - a first extraction branch and a second extraction branch connected to said main duct, wherein the first extraction branch serves the first portion of the hob and the second extraction branch serves the second portion of the hob, - a mobile deflector disposed in a connection point, - an actuator suitable for moving said deflector, - an electronic control unit operatively connected to the actuator of the deflector to control a movement of the deflector, and - detection means operatively connected to the electronic control unit and suitable for detecting a state of the burners respectively in correspondence of the first portion and of the second portion of the hob, wherein said extraction branches (20, 30) are mounted under the hob and lead to a first grille and a second grille respectively disposed near the first portion and and near the second portion of the hob, the main duct is mounted under said extraction branches (20, 30), the detection means are disposed in said hob, characterised in that said mobile deflector is disposed in said connection point which is between the main duct and the extraction branches (20, 30), in such a way to be: in a first position, wherein the communication between the main duct and the two extraction branches (20, 30) is enabled; a second position, wherein the communication between the main duct and the first extraction branch is enabled; a third position, wherein the communication between the main duct and the second extraction duct is enabled,