Laminar mixed convection heat transfer for aiding flow of air over a 5×1 in-line horizontal tube array centered between two vertical parallel plates is analyzed with the weighted residuals method. The flow regime is defined by 60 < Re < 500 and 0 < Gr < 53,000. The cylinder surfaces are assumed to have a uniform temperature while the walls are assumed to be adiabatic. Local data of two different geometries (cylinder-to-cylinder spacing Sid = 2, 3) are reported. Heat transfer data for all tubes in the array are normalized with the average Nusselt number for a single cylinder with identical hydrodynamic and thermal conditions. Data for both pure forced and mixed convection are presented for comparison purposes. Comparisons are made with previously reported experimental data for mixed convection over a single cylinder. It is shown that the thermal performance of the front sector of downstream cylinders is strongly affected by the presence of the upstream cylinders, while the backward sector of downstream cylinders remains basically uninfluenced by upstream cylinders.