Unsteady momentum and heat transfer from an asymmetrically confined circular cylinder in a plane channel is numerically investigated using FLUENT for the ranges of Reynolds numbers as 10≤Re≤500, of the blockage ratio as 0.1≤β≤0.4, and of the gap ratio as 0.125≤γ≤1 for a constant value of the Prandtl number of 0.744. The transition of the flow from steady to unsteady (characterized by critical Re) is determined as a function of γ and β. The effect of γ on the mean drag $$(\bar{C}_{\rm D})$$ and lift $$(\bar{C}_{\rm L})$$ coefficients, Strouhal number (St), and Nusselt number (Nu w ) is studied. Critical Re was found to increase with decreasing γ for all values of β. $$\bar{C}_{\rm D}$$ and St were found to increase with decreasing values of γ for fixed β and Re. The effect of decrease in γ on $$\overline{Nu}_{w}$$ was found to be negligible for all blockage ratios investigated.