This work is focused on a 2D numerical simulation of a thermal diffusion cloud chamber (TDCC) operating with water-helium mixture. We particularly address the impact of the stability of the vapor-gas mixture with respect to buoyancy-driven convective motion on homogeneous water nucleation rates. A comparison of our model results with Heist and Reiss results of nucleation of water in helium is first proposed. So, no convective fluxes are assumed within the TDCC and the critical supersaturation of water vapor is in agreement as obtained from numerical predictions. However, the influence of wall heating on the critical supersaturation results is found to be significant as obtained when convective transfers is accounted for within the TDCC and the results deviate significantly from those provided by Heist and Reiss. Their approach may lead large differences in terms of temperature, saturation ratio and nucleation profiles as it oversimplifies heat and mass transfer in TDCC compared to a 2D mass heat and momentum, model. Published by Elsevier Masson SAS.