Numerical solutions are presented for laminar, forced convection heat transfer in the thermal entrance region of circular sector ducts using the H1 and H2 thermal boundary conditions. With fully developed hydrodynamics, results are given for duct apex angles of 20°, 45°, 90°, 130°, 180°, 270°, and 360°. For the H1 condition, decreasing apex angle increases the duct corner effects, hence enhancing local and fully developed Nusselt numbers and shortening thermal entrance sections. For the H2 condition, the apex angle influences the thermal quantities differently. The data presented are compared with the limited available solutions and good agreement is found.