This paper focuses on the passive heat transfer enhancement where the flow surface is modified to increase the heat transfer. This field is narrowed by considering only techniques that are suited for high temperature applications in the range of 600-900 degrees C of the "cold" fluid. The scope to enhance heat transfer by the active method is limited due to the metallurgical properties of the tubes applied. Therefore several techniques have been proposed and applied to reduce the heat transfer resistance at the "cold" side, such as internally finned tubes, swirl inducers and helical shaped tubes. The penalty associated with enhancing the heat transfer is an increase in friction, which can be an important phenomenon for the application, for example in the production of ethylene by means of thermal cracking. In this study the results are presented to find the optimal heat transfer enhancement technique that has the lowest penalty in pressure drop for high temperature applications. The work has been executed by means of numerical simulations (CFD) of eight different available techniques. The numerical model is validated with heat transfer and pressure drop measurements for helical tubes. The validated model is subsequently applied on all the different heat transfer enhancement geometries. The results are compared with a reference straight tube as well. It is concluded that the helical tube yields the highest heat transfer at the lowest penalty with respect to pressure drop. The solid fins yield the lowest heat transfer enhancement and the highest penalty on pressure drop. (C) 2014 The Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.