Method for making and operating a concealed vent for ventilation, heating or air conditioning systems, comprising the following steps: S. 1.1) providing at least one ventilation conduit for introducing or drawing air in an environment to be ventilated, heated or cooled, where the ventilation conduit is concealed inside a wall which delimits the environment; S. 1.2) providing an air casing in turn comprising: - a box-shaped body in which a wall opening is obtained; and - a diffusor panel; s. 1.3) providing one or more fixing brackets or spacers arranged for fixing the diffusor panel to the box-shaped body; S. 1.4) arranging the diffusor panel in front of the wall opening so as to conceal it allowing the air coming from the at least one ventilation conduit to exit from the wall opening outside the same wall and be introduced in the environment, wherein the perimeter of the diffusor panel ideally contains the outer perimeter of the wall opening; S. 1.5) recessing and concealing the box-shaped body in the wall which delimits the environment to be ventilated, heated or cooled, wherein the wall opening is provided in the box-shaped body; - introducing air into the environment to be ventilated, heated or cooled, through a vacuum chamber obtained in the box-shaped body; - wherein the at least one ventilation conduit is arranged for introducing air in the air casing possibly joining thereto through respective connecting unions, characterised in that: - at least the perimeter edges of the diffusor panel project from the surface of the wall which delimits the environment by a maximum distance comprised between 0,2 centimetres and four centimetres; - the box-shaped body is without grids, fins and deflectors projecting into the vacuum chamber or through the wall opening and arranged for deviating and directing the airflow passing through the vacuum chamber and/or the wall opening; - the section available for the passage of air in the air casing is equal to or greater than 1.5 times the overall passage section of the air through all of the conduits or the connecting unions. S. 1.1) providing at least one ventilation conduit for introducing or drawing air in an environment to be ventilated, heated or cooled, where the ventilation conduit is concealed inside a wall which delimits the environment; S. 1.2) providing an air casing in turn comprising: - a box-shaped body in which a wall opening is obtained; and - a diffusor panel; - a box-shaped body in which a wall opening is obtained; and - a diffusor panel; s. 1.3) providing one or more fixing brackets or spacers arranged for fixing the diffusor panel to the box-shaped body; S. 1.4) arranging the diffusor panel in front of the wall opening so as to conceal it allowing the air coming from the at least one ventilation conduit to exit from the wall opening outside the same wall and be introduced in the environment, wherein the perimeter of the diffusor panel ideally contains the outer perimeter of the wall opening; S. 1.5) recessing and concealing the box-shaped body in the wall which delimits the environment to be ventilated, heated or cooled, wherein the wall opening is provided in the box-shaped body; - introducing air into the environment to be ventilated, heated or cooled, through a vacuum chamber obtained in the box-shaped body; - wherein the at least one ventilation conduit is arranged for introducing air in the air casing possibly joining thereto through respective connecting unions, characterised in that: - at least the perimeter edges of the diffusor panel project from the surface of the wall which delimits the environment by a maximum distance comprised between 0,2 centimetres and four centimetres; - the box-shaped body is without grids, fins and deflectors projecting into the vacuum chamber or through the wall opening and arranged for deviating and directing the airflow passing through the vacuum chamber and/or the wall opening; - the section available for the passage of air in the air casing is equal to or greater than 1.5 times the overall passage section of the air through all of the conduits or the connecting unions. - introducing air into the environment to be ventilated, heated or cooled, through a vacuum chamber obtained in the box-shaped body; - wherein the at least one ventilation conduit is arranged for introducing air in the air casing possibly joining thereto through respective connecting unions, - at least the perimeter edges of the diffusor panel project from the surface of the wall which delimits the environment by a maximum distance comprised between 0,2 centimetres and four centimetres; - the box-shaped body is without grids, fins and deflectors projecting into the vacuum chamber or through the wall opening and arranged for deviating and directing the airflow passing through the vacuum chamber and/or the wall opening; - the section available for the passage of air in the air casing is equal to or greater than 1.5 times the overall passage section of the air through all of the conduits or the connecting unions.