The flow structure and heat transfer characteristics of a square cylinder in cross flow are investigated numerically for both unconfined and channel-confined (blockage ratios, 10-50% in steps of 10%) flow situations at Reynolds numbers of 50, 100, and 150, and a Prandtl number of 0.7. As the blockage ratio is increased, the Reynolds number for the onset of vortex shedding increases and then decreases. Increases in Strouhal number, drag coefficient, pumping power, and cylinder Nusselt number are also observed with increasing blockage ratio. The enhancement of cylinder Nusselt number due to channel confinement is investigated for uniform heat flux and constant cylinder temperature boundary conditions.