An inlet assembly for a radiant burner, a turbulent flame burner or an electrically heated oxidiser, said inlet assembly comprising: an inlet nozzle defining a circular inlet aperture coupleable with an inlet conduit providing an effluent gas stream for treatment by said burner, a non-circular outlet aperture , and a nozzle bore extending along a longitudinal axis between said inlet aperture and said outlet aperture for conveying said effluent gas stream from said inlet aperture to said outlet aperture for delivery to said combustion chamber of said burner, said nozzle bore having a circular inlet portion extending from said inlet aperture, and an outlet portion extending to said non-circular outlet aperture , wherein a cross-sectional area of said inlet portion reduces along said longitudinal axis from said inlet aperture towards said outlet portion , and characterised in that the inlet assembly further comprises a baffle portion coupling said inlet portion with said outlet portion, said baffle portion defining a baffle aperture positioned within said nozzle bore, said baffle aperture shape: matching that of said outlet portion adjacent said portion , being symmetrically located within the baffle portion, and having a reduced cross-sectional area compared to that of said outlet portion adjacent said portion; wherein a cross-sectional area of said inlet portion transitions along said longitudinal axis from the cylindrical shape of said inlet aperture to a shape of said baffle aperture and reduces along said longitudinal axis from said inlet aperture towards said outlet portion to match said cross-sectional area of said baffle aperture . an inlet nozzle defining a circular inlet aperture coupleable with an inlet conduit providing an effluent gas stream for treatment by said burner, a non-circular outlet aperture , and a nozzle bore extending along a longitudinal axis between said inlet aperture and said outlet aperture for conveying said effluent gas stream from said inlet aperture to said outlet aperture for delivery to said combustion chamber of said burner, said nozzle bore having a circular inlet portion extending from said inlet aperture, and an outlet portion extending to said non-circular outlet aperture , wherein a cross-sectional area of said inlet portion reduces along said longitudinal axis from said inlet aperture towards said outlet portion , and characterised in that the inlet assembly further comprises a baffle portion coupling said inlet portion with said outlet portion, said baffle portion defining a baffle aperture positioned within said nozzle bore, said baffle aperture shape: matching that of said outlet portion adjacent said portion , being symmetrically located within the baffle portion, and having a reduced cross-sectional area compared to that of said outlet portion adjacent said portion; wherein a cross-sectional area of said inlet portion transitions along said longitudinal axis from the cylindrical shape of said inlet aperture to a shape of said baffle aperture and reduces along said longitudinal axis from said inlet aperture towards said outlet portion to match said cross-sectional area of said baffle aperture . <EOS>