Radiation view factors between opposed rectangular surfaces, between normal rectangular surfaces, and between cylinders and parallel rectangular surfaces are readily found in the literature. However, when the cylinder is located at the center of a rectangular duct, the view factors between the surfaces of the duct are obviously influenced by the presence of the cylinder; these view factors do not appear to be available in the literature. This article presents the view factors between the surfaces of a long duct, in which a long cylinder is located at its center, in terms of two dimensionless parameters: D/S, the ratio of the cylinder diameter to the length of the short side, and S/L, the ratio of the length of the short side to the length of the long side.