This study analyzed the effect of a slow pyrolysis process at a temperature range of 270–360℃ using a two-level factorial design. This pyrolysis process is limited to the process that occurs in the pyrolysis reactor, namely the decomposition process of raw materials into char and non-condensable gas. This study evaluated the effect of three process variables: fuel mass flow rate (0.006–0.008 kg/min), feedstock mass (2.5–4 kg), and residence time (120–180 min). The results showed that residence time had the most significant effect on pyrolysis products. Residence time contributes 30.1% to increasing char yield and correspondingly decreases non-condensable gas yield, indicating an inverse relationship. The feedstock mass and fuel mass flow rate show moderate effects, decreasing char yield by 16.1% and 6.2%, respectively, while inversely increasing non-condensable gas yield by the same magnitude. These findings underline the importance of residence time in determining char yield, especially in the slow pyrolysis process. This study also proves that the quantity of raw materials has an influence on char yield, although not as strong as the influence of residence time. The data revealed a clear trend, indicating how adjustments to the pyrolysis process can affect performance. With a longer residence time, it will produce a greater biochar than a non-condensable gas yield. Optimization of pyrolysis products must consider the balance between residence time, fuel heat rate, and mass of raw material load in order to obtain the optimal product as desired.