A housing for a radial fan, wherein the housing forms: - internally an impeller space accommodating an impeller rotatable about a rotation axis, - an air intake opening in direct communication with the impeller space, - an exhaust opening for exhausting an air-gas mixture from the impeller space outside the housing, - a gas inlet opening spaced apart from the air intake opening and in direct communication with the impeller space, so that the impeller space forms a space for mixing an air flow from the air intake opening with a gas flow from the gas inlet opening, - an air intake duct extending from the air intake opening which opens outside the housing to an inner end which opens in the impeller space, - a gas inlet duct extending from the gas inlet opening which opens outside the housing to an inner opening zone which opens in the impeller space at a distance from the inner end of the air intake duct, bypassing the air intake duct, wherein the air intake duct is parallel to the rotation axis and the gas inlet duct has an annular portion extending all around the air intake duct and which forms the inner opening zone, said inner opening zone comprising one or more gas openings extending or distributed along a circumference about the air intake duct, wherein a front wall of housing forms: - a truncated-cone-shaped portion which protrudes towards the outside of housing and externally delimits the annular portion of the gas inlet duct, and - a further protruding tubular portion converging from a smaller base, i.e. an outer end of the truncated-cone-shaped portion towards the inside of housing and forming an inner portion of the air intake duct and said inner end, the housing further comprising an inner wall which delimits the gas inlet duct from the inside of the housing, characterized in that the inner opening zone of the gas inlet channel is formed along a first meeting line between the inner wall and the front wall at the smaller base of the truncated-cone-shaped portion, so as to prevent the establishment of a Venturi effect between the air flow and the gas flow entering into the impeller space. - internally an impeller space accommodating an impeller rotatable about a rotation axis, - an air intake opening in direct communication with the impeller space, - an exhaust opening for exhausting an air-gas mixture from the impeller space outside the housing, - a gas inlet opening spaced apart from the air intake opening and in direct communication with the impeller space, - an air intake duct extending from the air intake opening which opens outside the housing to an inner end which opens in the impeller space, - a gas inlet duct extending from the gas inlet opening which opens outside the housing to an inner opening zone which opens in the impeller space at a distance from the inner end of the air intake duct, bypassing the air intake duct, the air intake duct is parallel to the rotation axis and the gas inlet duct has an annular portion extending all around the air intake duct and which forms the inner opening zone, said inner opening zone comprising one or more gas openings extending or distributed along a circumference about the air intake duct, wherein a front wall of housing forms: - a truncated-cone-shaped portion which protrudes towards the outside of housing and externally delimits the annular portion of the gas inlet duct, and - a further protruding tubular portion converging from a smaller base, i.e. an outer end of the truncated-cone-shaped portion towards the inside of housing and forming an inner portion of the air intake duct and said inner end, - a truncated-cone-shaped portion which protrudes towards the outside of housing and externally delimits the annular portion of the gas inlet duct, and - a further protruding tubular portion converging from a smaller base, i.e. an outer end of the truncated-cone-shaped portion towards the inside of housing and forming an inner portion of the air intake duct and said inner end,