The use of porous media in the combustion chamber is a very efficient method to reduce pollution and energy consumption. These burners have advantages over free flame burners because of less production of NOx, preheating the mixture of fuel and air before firing, and smaller size of the burner at the same firing rate. In porous burners, all three mechanisms of heat transfer, namely conduction, Convection, and radiation are present, whereas in the free flame burners the convection mechanism is the major factor for heat transfer. Open-Range triggering, uniform distribution of heat in the combustion chamber, faster warm-up and significant reduction of noise are other advantages of this type of burners that favor the use these burners frequently in various applications. The present study experimentally investigates properties of porous media and their performance as burners with different firing rate, as compared to an existing free flame burner. A mixture of air and natural gas is used as the feed fuel. The porous burner was designed such that the combustion mixture enters into a cylindrical porous medium along the axial direction and exits in radial direction. The location of flame at radial direction is monitored by using thermocouples fitted in several radial locations. There are generally four types of flames in porous media burners. Only two types, submerged combustion and surface combustion, of these are observed are studied in this research. The measuring station for species concentration is at the exit of the combustion chamber. After stabilizing each flame to achieve a steady-state condition, the effects of equivalence ratio and firing rate on the performance of porous and free burners were examined. In this study, three sets of experiments were performed. First the performance of the porous burner and its exhaust gas analysis performed while the exhaust damper was fully opened. Next, the effect of back-pressure on porous burner performance and pollution was studied by adjusting the exhaust damper. Finally, the performance of a free flame burner, and its pollution was investigated. Results show that in a porous medium having 26.2 mm length, surface combustion and submerged combustion take place. The porous burner operating at equivalence ratio of 0.9 (submerged combustion) has performed better than when operating at the equivalence ratio of 0.8 (surface combustion). Increased firing rate in porous medium burner led to increased concentrations of NO and CO2, and reduced volume fractions of CO and O2. Closing the exhaust damper has no significant effect on the amount of O2 and CO2, and causes a small decrease in the concentration of CO, and a small increase in NO concentrations. The characteristics and performance of a conventional free-flame burner were also determined and compared with the porous burner. Results show that increasing equivalence ratio in conventional burner increases the concentration of CO, NO and reduces the concentration of O2 in combustion products. Also increasing firing rate cause an increase in concentration of NO and a decrease in CO. However, it does not have a significant effect on the concentration of O2 and CO2. Keywords : : porous, Burner, Air pollutants, equivalence ratio, porous Burner, fireing rate