In the present study we investigate the buoyancy induced turbulent flow characteristics in a ceiling ventilated horizontal channel with an internal heat source. Numerical analysis is performed in the channel for two different Grashof number Gr=7.88 × 1011 and 1.18 × 1012 and the volumetric blockage ratio is varied from 0.012 to 0.055. It is found that by increasing the Grashof number to Gr=1.18 × 1012, the net mass flow rate through the central, upstream and downstream vents are increased by 23%, 16% and 15% respectively. It is also identified that by increasing the volumetric blockage ratio, the average temperature for Gr=7.88 × 1011 and 1.18 × 1012 are increased by 26.4% and 38.6%; while the average longitudinal velocity are decreased by 56% and 44% respectively. © IAEME Publication.