It is well known that most of the heat losses of buildings occur at outer walls, which are made of a few layers such as plaster, wall bricks, insulation material, etc. It is required that the wall bricks having a low overall heat transfer coefficient to reduce heat losses through buildings to increase the heating performance of buildings. In order to address the requirement, the wall bricks are produced of low thermal conductivity materials and with cavities (hole), weakening the thermal transport mechanism. This study, is aimed to decrease the overall heat transfer coefficient of wall brick models with various cavities, which affect the natural convection mechanism. For this purpose, some changes are made to the cavity geometry of a single cell of the hollow wall brick model. The proposed geometries' heat transfer experiments were repeated under three different (7, 9, 12 W) thermal power conditions. The building is simulated as an insulated chamber made of extruded polystyrene (XPS) with 300 mm x 300 mm x 300 mm. The wall brick models are produced from polyvinyl chloride (PVC) material in 160 mm x 160 mm x 50 mm and mounted to a wall of the insulated chamber. The experiments are carried out on the brick models with the cavity geometries of regular symmetrical I and asymmetrical Z profiles. The temperatures are measured at 3 points on both sides of the brick models. It has been measured that the overall heat transfer coefficient of the Z model is lower than that of the regular I profile at 7.1%, depending on the heat transfer direction.