The present work is devoted to experimentally investigate the characteristics of the convective heat transfer and pressure drop of pure water in the tube side of vertical helically/conically coiled tube in tube heat exchangers. This work is performed at different geometrical parameters of the coils and at different operating conditions of the tube side. Six concentric coiled tube in tube heat exchangers of counter-flow configurations are constructed; three are helically coiled with different torsions, and the others are conically coiled with taper angle of 45*. Wilson plot method is used to investigate the thermal performance results in terms of tube average heat transfer coefficient, average Nusselt number and fanning friction factor. The results showed that the internal tube of conical heat exchangers has a lower heat transfer coefficient and lower friction factor compared with that in the helical coil, while the conical coil of taper angle 45* provides a higher hydrothermal performance compared with the helical coil. Empirical correlations are developed to predict the tube-average Nusselt number and fanning friction factor.