This paper reports results of an experimental and theoretical study of the air flow in a vertical stack driven by thermal buoyancy and induced by surrounding wind. Tubular stacks with water jacket were constructed for experiments. To investigate the effect of the buoyancy force on the air flow, hot water was circulated through the stack jacket each experimental case with a different temperature. The effect due to the surrounding wind was studied using a wind tunnel to produce wind at different velocities. In this study, a simple model was developed to characterize the air flow caused by the effects. From the experimental validation, it was found that the model can predict well the volumetric rate of the air flow in the stack.