Homogeneous mixing of hot air from the hot blast stove with suitable quantity of cold air in a mixing chamber is very essential to maintain uniform temperature of hot air at all tuyers of a blast furnace. Proper design of the mixing chamber is very important for stable and efficient operation of blast furnace, lower energy consumption, and lower carbon dioxide emission. Comprehensive understanding of the physics of the mixing process is very essential for efficient design of the mixing chamber. In this paper, computational fluid dynamics (CFD) simulations are conducted to analyze the mixing of hot and cold air in a tangential cold gas inlet type and in a radial cold gas inlet type mixing chambers, which are commonly used in the industry. Results show that both types of mixing chamber produce very non-homogeneous mixture of cold and hot air despite having large mixing length in the long hot blast main. Also, design of a novel compact mixing chamber is presented and CFD analysis of this mixing chamber is conducted. The new mixing chamber is found to produce almost homogeneously mixed air stream within a very short length due to very high turbulence of the intensely swirling air flow. Also, the new mixing chamber is found to save large amount of high-quality thermal energy, which is wasted in the other two designs through the wall of the long hot blast main.