Three-dimensional, transient calculations have been made for flow far downstream in a horizontal, bottom heated, aspect ratio 2 duct with throughflow in the low supercritical Rayleigh number (Ra) and low Reynolds number (Re) regime. The two flow types present are longitudinal rolls and distorted, convecting transverse rolls. Longitudinal rolls results confirm previous studies. Ra and Re dependence of the transverse rolls flow field is investigated. The Nusselt number (Nu) is seen to be essentially independent of Re, and perhaps also of the flow regime. Isotherms and velocity Vector plots are presented. Comparisons are made with published experimental and numerical results.