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 $\beta =1/3,1/4,\u2003and\u20031/6$. Effect of aiding and opposing buoyancy is brought about by varying the Richardson number in the range $-1.0\u2264Ri\u22641.0$. At a blockage ratio of $1/3$, suppression of vortex shedding is found at Ri = 1, whereas von Kármán vortex street is seen both at $\beta =1/4$ and $1/6$, 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 $\beta =1/3$. For all $\beta $, heat transfer increases with increasing Ri. Flattening of $Nuavg$ –Ri curve beyond $Ri>0.75$ is observed at $\beta =1/3$.