A coupled simulation of the flue gas and process gas side of the convection section of a steam cracker is performed, making use of the CFD software package Fluent. A detailed overview of the operating mode of the different heat exchangers suspended in the convection section is obtained. The asymmetric inlet flow field of the flue gas in the convection section, and the radiation from the convection section walls leads to large differences in outlet temperatures of the tubes located in the same row. The flow fields and temperature fields in the tubes of a single heat exchanger differ significantly with e.g., outlet temperatures of the hydrocarbon-steam mixture ranging from 820 K to 852 K. Moreover, the simulations reveal the presence of hot spots on the lowest tube row, possibly causing fouling. (C) 2009 American Institute of Chemical Engineers AIChE J, 55:2773-2787, 2009