A partially premixed methane/air flame in a two-dimensional configuration was studied in this work. The configuration was close to those used in real domestic boilers. The flame structure and flow pattern were calculated by implementing a complex chemistry and detailed transport formulation in an industrial computational fluid dynamics code (ESTET). A postprocessing method was used to predict NO emission. Computations were performed for two configurations. The two cases had the same primary and secondary mass flow rates and equivalence ratios. The only difference between them was the introduction of an insert inside the primary injector. Both results were compared with measurements. In both cases, calculations were in good agreement with the flame shapes observed experimentally. The classical burner showed a Bunsen-type flame, while the one with an insert had a totally different shape (butterfly-type flame). NO emission levels were also well predicted in both configurations. The butterfly flame induced a reduction in NO emission. The reduction seemed to be due to the increased mixing between the burned gases and the secondary air jet, which homogenized the temperature distribution and reduced the maximum temperature. These calculations combined with the postprocessing technique for NO prediction needed only few hours of CPU time on a classical workstation. This demonstrates the possibility for burner and boiler manufacturers to use numerical simulations to predict relatively complex configurations in terms of flame structure and pollutant emissions.