Results from an experimental investigation of natural convection heat transfer from a vertical array of three evenly heated horizontal cylinders, with dissimilar cylinder spacings, is presented. Nusselt numbers are presented for Rayleigh numbers 1.96E7 and 5.35E7 with separation distances 2D, 3D, 4D, and 5D. The results show that the Nusselt number on the second cylinder, in the three-cylinder array, increases compared to the lowermost cylinder for both Rayleigh numbers investigated and all four separation distances. The Nusselt number for the upper cylinder in the array increases compared to the lowermost/unconfined cylinder, but is comparable to the middle cylinder for the separation distances investigated. Enhanced heat transfer due to turbulent mixing on the upper cylinders in the array is discussed. (C) 2012 Elsevier Ltd. All rights reserved.