The goal of the present work is to develop and test in detail a numerical algorithm for solving the problem of complex heat transfer in hollow bricks. The finite-difference method is used to solve the governing equations. The article also provides a detailed description of the procedure for thickening the computational grid. The flow regime inside the hollow brick is turbulent, which is a distinctive feature of this work. As a rule, if the size of the cavities in the brick is greater than 20 cm and the temperature difference in the considered solution region is significant, then the numerical solution can be obtained in the turbulent approximation. The effect of surface emissivities of internal walls on the thermal transmission and air flow inside hollow brick is investigated. The distributions of isolines of the stream function and temperature are obtained. The results report that the emissivity of interior surfaces significantly affects the heat transfer through hollow bricks.