In this study, an investigation on the influences of different manufacturing techniques on the heat transfer and pressure drop in the developing and fully developed regions of mini-tube under different flow regimes is introduced. The purpose of this research is to experimentally investigate the heat transfer and pressure drop characteristics using 3D-printed tubes and traditional stainless steel tubes in the vertical direction under isothermal and non-isothermal boundary conditions. Experiments are conducted using distilled water (Prandtl numbers varying from 4 and 7) at Reynolds numbers of 800-10000 with heat fluxes between 30 and 500 kW&#183;m<sup>-2</sup>. Test tubes with inside diameters of 2 mm are used, and the average surface roughness is 1.6 &mu;m and 15.3 &mu;m, respectively. The results are compared with previous studies. It is verified that the heat transfer characteristics are almost the same for the traditional tube and the 3D-printed tube in the laminar region. The average deviation between these two tubes is 7.7&#37;. However, for the turbulent region, the Nusselt numbers of 3D-printed tube in the turbulent region increases by an average of 45&#37; as compared with a traditional tube. The friction factors under heating conditions also increased by an average of 209&#37;. In addition, the 3D-printed tube enters the transition region earlier. The results show that the average critical Reynolds number of a traditional tube and 3D-printed tube is around 2300 and 2000, respectively. Correlations in the turbulent region are developed to predict the friction factors and heat transfer coefficients with good accuracy.