The ablative reactor may be employed to enable fast pyrolysis to produce bio-oil from relatively large-sized biomass samples. Ablation mainly involves direct compressive force and conductive heat transfer between a hot surface and the biomass materials. Temperature evolution and heating rates are important operating factors in the biomass thermal conversion process. In this work, experimental and analytical investigations were carried out for different vertical dimensions of the biomass samples (2-20mm) and hot plate temperatures (400-550°C). It was shown that the thermal characteristics of the biomass were mainly affected by the transient conditions. It was observed that volatile release occurred during the transient heat transfer periods. It was found that at the maximum hot plate temperature of 550°C, the highest heating rate that could be achieved by ablation was more than 600°C/min.