For wood combustion in small appliances where incomplete combustion occurs, it is very important to distinguish between flue gas methane and non methane hydrocarbons to give a good evaluation of nanoparticle emissions. While non methane hydrocarbons are gaseous at stack temperature they may contribute to the formation and growth of nanoparticles in the atmosphere. For this purpose, a study is carried out to investigate the influence of non methane hydrocarbons in the formation of nanoparticles in the quenched and diluted flue gas generated by a closed fireplace (11 kW) with natural air draft and fed with beech wood logs. The particle number concentration and size distribution measurements were conducted in parallel with an electrical low pressure impactor (ELPI) and a fast mobility particle sizer (FMPS). Two analyzers with flame ionization detection have been used for gaseous organic carbon measurements based respectively on chromatographic separation and on catalytic process. The different combustion phases of the closed fireplace (ignition, stable flame, extinction) are observed to significantly affect the formation of nanoparticles triggered by the presence of non methane hydrocarbons in the cooled flue gas. ; SeriesInformation ; Proceedings of the 20th European Biomass Conference and Exhibition, 18-22 June 2012, Milan, Italy, pp. 723-727