In the present study, the steady-state natural convection heat transfer from a vertical array of a pair of horizontal cam cross-sectional tubes under constant heat flux submerged in water is experimentally investigated. The experiment is carried out for the modified Rayleigh number range of to, and a dimensionless tube spacing range of 1.5, 2.0, and 2.5. The effects of the modified Rayleigh number, cam tube orientation, and dimensionless spacing on the heat transfer rate from the individual tube and the vertical tube array are studied. Based on the results obtained, the effect of thermal plume on the heat transfer rate from the upper cam tube in the vertical array is strongly dependent on the dimensionless spacing. Under fixed conditions, the mean convection coefficient of the single horizontal cam tube with the downward orientation is higher than that of the other orientations for all the modified Rayleigh numbers considered.