The use of V-trough concentrators offers a simple approach to increasing the radiation incident on a solar receiver; this is particularly useful for increasing the temperature in thermal systems. However in order to accurately predict the performance of thermal systems under concentrated radiation, there is a need to understand the heat loss from them. This study experimentally shows that, for a laterally and longitudinally inclined enclosed V-trough concentrator, the natural convection heat loss can be predicted using an equation of the form Nu = aRa(b) for Rayleigh numbers between 2 x 10(3) and 1 x 10(8). It is suggested that the relationship is a good representation of heat transfer in enclosed V-trough concentrators under most practical orientations, and thus lends itself for implementation into design models for V-trough concentrators. (C) 2013 Elsevier Ltd. All rights reserved.