In this present paper, a coupled 3D thermo fluid-thermo mechanical modelling approach of a plate type air pre-heater is introduced. The conjugate heat transfer within the pre-heater is numerically solved using 3D computational fluid dynamics. The model considers the discrete structure of the whole pre-heater assembly including the air channels, plates and manifold ports. Wall surface and gas temperature measurements are performed using thermocouples to validate the numerically predicted calculations. The results show good agreement, implying that the proposed model can be used in the design and process optimisation of the air pre-heater. Moreover, a submodel created from the thermofluid analysis has been used to investigate the thermomechanical behaviour of the air pre-heater manifold region using the nonlinear finite element method. The nonlinear elastic-plastic behaviour of the material has been considered. The component locations susceptible to stress could be determined. The approach results in reduced prototype costs and product development time in the design and optimisation of efficient air pre-heater designs. Copyright (C) 2011, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.