A 1/13 scaled model tunnel is constructed in order to investigate the blockage effect (the ratio of the model cross sectional area to the tunnel cross sectional area) on the heat release rate inside the tunnel with different ventilation velocities. Scaling is done based on Froude number. In the experiments, wood sticks assembled in different geometrical configurations are burned with various longitudinal ventilation velocities inside the model tunnel. Combustion gases are sampled to calculate the heat release rate. A statistical model is developed using the analysis of variance (ANOVA) method. According to the statistical model, 79.8% of the variation in heat release rate is attributed to changes in blockage ratio, 10.6% to changes in thickness, and 4.5% to changes in velocity.