This work presents a fully-coupled gas-phase and particle model for the synthesis of narrowly-distributed silicon nanoparticles from the thermal decomposition of silane, which simultaneously solves the kinetic mechanism of Swihart & Girshick (1999, J. Phys. Chem. B 103 64-76) with a detailed particle model. The model was applied to simulate the hot-wall reactor and process conditions of Koermer et al. (2010, J. Aerosol Sci. 41 998-1007). It was found that after a short burst of inception and condensation, growth occurred through coagulation and sintering of small particles into larger primaries. The sintering parameters were estimated by fitting the mode and variance of the experimental primary particle PSD to experimental data. Excellent agreement was obtained for four cases at a range of temperatures and residence times. The model is additionally in qualitative correspondence with homogeneous nucleation theory and comparison of TEM-style images is encouraging.