The aim of the present study is to achieve conjugate heat transfer enhancement in a finned heat exchanger by only modifying the isotherms distribution in the fins. A three-dimensional numerical study of a flat plate and its geometric variants is therefore carried out for a steady incompressible laminar flow. The results are analyzed by carrying out an extensive analysis of the local field synergy which shows the effect of local velocity and local temperature gradient vectors on the heat transfer process. Depending upon the magnitudes of the field synergy parameters, in general, it is found that the local heat transfer coefficient is in accordance with the field synergy principle for the regions in the thermal boundary layer very close to the heated surface. Gain in thermal performance is obtained due to orientation of the velocity and the temperature gradient vectors in the same direction near the upstream fin modification as well as due to the enhancement of the modulus of the inner product of velocity and temperature gradient. For one of the tested configurations, the results show an increase of 7% of PEC associated with about 14.4% less aluminum material used. © 2017 Elsevier Ltd