Natural convection heat transfer from multiple/stack of horizontal cylinders is often seen in steel manufacturing industries. In this context, a numerical study of natural convection heat transfer from a stack of three horizontal hollow cylinders in a three-dimensional turbulent regime is presented in this work. A finite-volume method-based computational fluid dynamics simulations are performed for a range of length-to-diameter ratio of the cylinders ( \(0.5\le L/D\le 20\) ) at Rayleigh number, \(\text {Ra}=10^{10}-10^{13}\) in turbulent natural convection flow regime. Both flow and thermal fields, along with the heat loss from the stack of cylinders, are effectively captured by solving the coupled Reynolds-averaged Navier-Stokes (RANS) and thermal energy equations. Results unveil that the average surface Nusselt number, Nu, from the inner surfaces of the hollow cylinders decreases with rise in L/D while it is almost constant for the outer surfaces. Thus, the total average Nu shows a decreasing trend with rise in L/D. However, both average Nu and total heat loss, Q, significantly rise with increasing Ra. An empirical correlation for the average Nu is also developed in this work based on the dimensionless parameters L/D and Ra considered in this study.