A variety of nanowires can be grown in a tube furnace via the transport of evaporated species by a carrier gas toward substrates. The insufficient understanding and the resulting limited control typical for this research area motivated us to systematically study the distribution of the growth species in such processes and evaluate its effect on the nanowire growth. Calculations based on simple considerations as well as more sophisticated numerical (COMSOL) simulations were utilized to follow the time evolution of the species distribution at different carrier gas pressures and flow rates. We demonstrate that the balance between diffusion and convection must be appropriately tuned to ensure steady growth conditions (not achieved in many of the previously reported experiments). Experimental data of Si and ZnO nanowires growth is presented and supports the simulations. Insight into the appropriate design of nanowires growth experiments and a universal basis to compare between the results of different laboratories are provided.