A comprehensive numerical model for selective low-pressure chemical vapor deposition (LPCVD) of tungsten from hydrogen and WF6 in a single-wafer reactor has been developed. The computational fluid dynamics (CFD) code PHOENICS-CVD is used for transient solutions of the two-dimensional transport equations of heat, momentum and chemical species in the reactor. A detailed model is used for the kinetics of tungsten deposition at the surface. A model for the nucleation of intermediates, which are formed at the surfaces where tungsten is deposited and are transported through the gas phase, is used to describe the loss of selectivity. This opens the way for qualitative study of the influence of process conditions and reactor configurations on the selectivity of this process. The selectivity is found to improve at high how rates, low total pressures and low partial pressures of WF6.