A mixer device for combustible gas burners, comprising: - a fan unit with an impeller having radial blades driven about an axis of rotation and with an axial intake section and a radially opposed delivery section, - a manifold for housing the impeller of said fan, - a first duct having a terminal portion converging towards the intake section for supplying a flow of air to the intake section, said first duct being coaxial with the axis of rotation, the free end of said portion having a minimum cross section, - a second tubular duct for supplying a flow of gas at the end of the terminal portion having the minimum cross section, said second tubular duct being formed at least partially inside the first duct and coaxial with the first duct, in such a way that the flow of air is mixed with the flow of gas upstream of the fan intake section, - the blades of the impeller projecting from a base surface of the impeller, each blade having a leading edge located in the intake section, these leading edges forming the mouths of corresponding blade channels between adjacent pairs of blades, extending between the intake section and the delivery section of the fan, - the fan housing manifold having a front surface profile positioned in front of the impeller blades and spaced apart from them, characterized in that it comprises at least one appendage which is located outside the first converging duct and projects from said first converging duct in a direction away from said axis, the at least one appendage extending in an area delimited jointly by the terminal portion of the first converging duct, by the imaginary extension of this portion towards the base surface of the impeller, on the side of the impeller base surface nearer to the leading edges of the blades, by the leading edges of the blades, with said appendage being spaced apart from the blades of the impeller in order to avoid interference with said blades, and by the front surface profile of the fan housing manifold which is positioned in front of the blades of the impeller in the proximity of the corresponding leading edges of the blades, said at least one appendage being located in said area such as to oppose fluid dynamic actions of the combustible mixture created at the intake section of the impeller. - a fan unit with an impeller having radial blades driven about an axis of rotation and with an axial intake section and a radially opposed delivery section, - a manifold for housing the impeller of said fan, - a first duct having a terminal portion converging towards the intake section for supplying a flow of air to the intake section, said first duct being coaxial with the axis of rotation, the free end of said portion having a minimum cross section, - a second tubular duct for supplying a flow of gas at the end of the terminal portion having the minimum cross section, said second tubular duct being formed at least partially inside the first duct and coaxial with the first duct, in such a way that the flow of air is mixed with the flow of gas upstream of the fan intake section, - the blades of the impeller projecting from a base surface of the impeller, each blade having a leading edge located in the intake section, these leading edges forming the mouths of corresponding blade channels between adjacent pairs of blades, extending between the intake section and the delivery section of the fan, - the fan housing manifold having a front surface profile positioned in front of the impeller blades and spaced apart from them, characterized in that it comprises at least one appendage which is located outside the first converging duct and projects from said first converging duct in a direction away from said axis, the at least one appendage extending in an area delimited jointly by the terminal portion of the first converging duct, by the imaginary extension of this portion towards the base surface of the impeller, on the side of the impeller base surface nearer to the leading edges of the blades, by the leading edges of the blades, with said appendage being spaced apart from the blades of the impeller in order to avoid interference with said blades, and by the front surface profile of the fan housing manifold which is positioned in front of the blades of the impeller in the proximity of the corresponding leading edges of the blades, said at least one appendage being located in said area such as to oppose fluid dynamic actions of the combustible mixture created at the intake section of the impeller.