In this paper for the mechanisms of pool boiling heat transfer a mathematical model is derived based on statistical treatment. No additional new empirical constant is introduced. The proposed model for pool boiling heat flux is found to be a function of wall superheating, minimum and maximum active cavity sizes, the contact angle, and physical properties of fluid. It also turns out that the present model well explains the mechanism of how wettability affects the boiling heat flux. The model predictions are compared with the existing experimental data, and fair agreement is found for different contact angles.