This work looks at the design of finned surfaces, explores existing generalised correlations and further shows the development of new ones. The aim is to develop correlations with the following features: a) the range of validity of the Reynolds number is extended from laminar to turbulent regimes, and b) the correlations are a function of the fin geometry. In this work new generalised correlations for finned surfaces of the plain triangular type are developed and validated against experimental data and other existing generalised correlations. The new correlations are implemented in a design methodology. The results indicate that compared with experimental data, the average absolute error is 5 % for the friction and 7 % for Colburn factor. In design, the exchanger size results in smaller volumes down to 41 % compared with the use of published correlations.