Method for making a concealed vent for ventilation, heating or air conditioning systems, comprising the following steps, not necessarily in sequence: S. 1) providing a ventilation conduit for feeding or drawing air in an environment to be ventilated, heated or cooled, wherein the ventilation conduit is concealed inside a wall which delimits the environment and exits outside the same through a wall opening; S. 2) providing at least one fixing spacer on which the following are obtained: - at least one spacer-fixing zone arranged to fix the spacer to the ventilation conduit; and - at least one spacer-supporting zone arranged to support the fixing spacer against the outer surface of the wall; S. 3) fixing a diffuser panel to the at least one fixing spacer; S. 4) fixing the at least one fixing spacer to one or more zones of the ventilation conduit and at the same time supporting the fixing spacer against the outer surface of the wall, so that the diffuser panel comes to be located in front of the wall opening concealing the same and allowing the air coming from the ventilation conduit to come out from the wall opening and be fed in the environment, where the perimeter of the diffuser panel ideally contains the outer perimeter of the wall opening, and at least the perimeter edges of the diffuser panel project from the surface of the wall which delimits the environment for a predetermined maximum distance, where the at least one fixing spacer allows the mutual position between the at least one spacer-fixing zone and the at least one spacer-supporting zone to be reversibly adjusted. S. 1) providing a ventilation conduit for feeding or drawing air in an environment to be ventilated, heated or cooled, wherein the ventilation conduit is concealed inside a wall which delimits the environment and exits outside the same through a wall opening; S. 2) providing at least one fixing spacer on which the following are obtained: - at least one spacer-fixing zone arranged to fix the spacer to the ventilation conduit; and - at least one spacer-supporting zone arranged to support the fixing spacer against the outer surface of the wall; - at least one spacer-fixing zone arranged to fix the spacer to the ventilation conduit; and - at least one spacer-supporting zone arranged to support the fixing spacer against the outer surface of the wall; S. 3) fixing a diffuser panel to the at least one fixing spacer; S. 4) fixing the at least one fixing spacer to one or more zones of the ventilation conduit and at the same time supporting the fixing spacer against the outer surface of the wall, so that the diffuser panel comes to be located in front of the wall opening concealing the same and allowing the air coming from the ventilation conduit to come out from the wall opening and be fed in the environment, where the perimeter of the diffuser panel ideally contains the outer perimeter of the wall opening, and at least the perimeter edges of the diffuser panel project from the surface of the wall which delimits the environment for a predetermined maximum distance, where the at least one fixing spacer allows the mutual position between the at least one spacer-fixing zone and the at least one spacer-supporting zone to be reversibly adjusted.