The present work investigates the mixed convective flow and heat transfer characteristics past a triangular cylinder placed symmetrically in a vertical channel. At a representative Reynolds number, Re = 100, simulations are carried out for the blockage ratios . Effect of aiding and opposing buoyancy is brought about by varying the Richardson number in the range . At a blockage ratio of , suppression of vortex shedding is found at Ri = 1, whereas von Kármán vortex street is seen both at and , respectively. This is the first time that such behavior of blockage ratio past a triangular cylinder in the present flow configuration is reported. Drag coefficient increases progressively with increasing Ri and a slightly higher value is noticed at . For all , heat transfer increases with increasing Ri. Flattening of –Ri curve beyond is observed at .