Natural-convection heat transfer in enclosed horizontal N × N arrays of heated rods with a constant heat flux dissipation is numerically investigated. For a fixed rod diameter d, the width of the isothermal outer enclosure W is fixed at W/d = 20.33. Furthermore, the pitch-to-diameter ratio of the arrays is fixed at P/d = 1.33. The average Nusselt number of each rod Nud in N = 3, 5, 7, and 9 arrays is predicted for a modified Rayleigh number range of 1 to 316 with a constant Prantdl number of Pr = 0.7. Pure conduction results are also obtained for rod bundles ranging from 3 × 3 to 13 × 13. The conduction Nusselt number of the corner rod in the array is found to decrease with the increase in N from 3 to 7. However, the trend reverses, and the Nusselt number begins to increase for N > 9. The convection results show that the bottom-row rods experience the maximum variation in their local Nusselt numbers. For a given , the Nud of the rods is found to decrease with the increase in the row number (from bottom to top). The streamlines show that there is significant flow activity in the enclosure, especially in the top-half region. For arrays with N = 3 to 9, significant convection heat transfer is observed even at = 1. This horizontal orientation with distributed energy sources within the enclosure is suspected to be an inherently unstable phenomenon. The isotherms clearly show that the majority of the energy generated within the enclosure is transferred to the top and side surfaces. In these arrays, for the range of investigated, >50% of the total power input is transferred to the top surface, while the bottom surface receives <2% of the total. For each array, the overall enclosure Nusselt number is correlated as a function of the enclosure-modified Rayleigh number. The enclosure Nusselt number increases as the order of the array N is increased from 3 to 9. The reported correlations can be readily used to estimate the maximum temperatures in the N = 3 to 9 arrays.