Thermal interactions of heat exchanger fluids with the surroundings are difficult to limit. It becomes a necessity to determine the effect of these interactions on exchanger performance when the demand of heat exchanger effectiveness is very high, like in case of cryogenic applications. In the present article, effect of heat in-leak in two-stream cross flow exchangers has been studied and compared with the two other type of flow arrangements, namely counter-current and co-current. Mathematical model involving mutual heat exchange between hot and cold fluid streams and their individual thermal interactions with ambient have been considered through overall heat transfer coefficients. Parametric studies have been made with different non-dimensional parameters and essentially generating effectiveness-NTU type of plots for balanced exchangers. Various heat exchange possibilities depending on the relative temperature difference between fluids and ambient have been considered. (C) 2013 Elsevier Ltd. All rights reserved.