Traditional biomass cookstoves (TCS) are very popular among rural areas and street vendors especially in developing and underdeveloped nations due to their conventional process and simple construction. However, this direct combustion technique is not suitable due to poor efficiency and harmful gaseous-particular emission. Improved biomass cookstoves (ICS) have the potential to overcome the health and environmental problems that are common in the case of TCS. In the present study, investigations were carried out on 3.5 kWth ICS based on gasification design with four different air conditions. The opening to the closing ratio of primary to secondary air vents are taken at 50/50, 50/100, 60/100, and 80/100, respectively for the experiments. Performance of TCS and different ICS cases were compared in terms of burning rate, specific fuel consumption, firepower, useful firepower, thermal efficiency, total particulate matter, and gaseous emissions (CO, CO2, O2, NOx, CC, HC). Apart from that, thermal analysis such as mass balance, energy balance, and exergy efficiency was also calculated. 50/100 opening to the closing ratio of primary to secondary air offers the better performance in terms of higher thermal efficiency and lower gaseous and particulate emission is the major conclusion from this study.