The utilization of biomass briquettes used as an alternative fuel can replace fuel oil, especially kerosene and gas, which has not been very effective in its journey because several factors influence it. Therefore, it is important to improve the stove, which functions to transfer heat from biomass briquettes to make the cooking quality more effective. So this study aims to utilize coconut shell waste briquettes as fuel on a stove whose combustion chamber is modified by varying the diameter of the aluminum cylinder. The results showed that the variation of the cylinder diameter 180mm was the most superior in terms of fire temperature, water boiling ability, and thermal efficiency of 514oC, 30 liters, and 37.74%.