The final stage of heat treatment of steel mill balls - tempering is carried out in high-performance through-type furnaces with a convective type of heat transfer. In such furnaces, the cage is located on a moving conveyor in a single layer, which ensures the production of products with uniform properties. Furnaces of this type consist of chambers for heating and holding balls. The article considers the design of the heating chamber, which consists of single sections, equipped with the same type of block-type devices. The heating of the metal in the block is carried out by jet blowing the surface of the balls with a heated gas stream circulating inside its body using a high-temperature fan. On the basis of the proposed method, a computational analysis of several thermal regimes of the heating chamber was carried out. The effect on the parameters of the furnace operation of changing the assortment of processed balls, as well as the performance of the circulation fan, was studied. It has been established that the efficiency of the heating chamber significantly depends on the diameter of the metal being processed, so when heating balls with a diameter of 120 mm, the efficiency is 0,71, and with a diameter of 40 mm, only 0,47, respectively. Reducing the mass of conveyor parts by 1,5 times increases the efficiency of the furnace to 0,75. Increasing the performance of the circulation fan by 2 times from 14,000 m3/h to 28,000 m3/h reduces the required coolant temperature by 50-230 °C, which increases the reliability of its running gear. The materials presented in the article can be useful in the development and design of furnaces with a convective type of heat transfer.