Effect of magnetic field orientation on free convection of several water–based nanofluids in a square porous cavity is analyzed in this study. To this aim, the heatline visualization technique is implemented for the first time. Moreover, streamlines and isotherms are employed to present fluid flow and temperature distribution. The governing equations are transformed into a dimensionless form and then solved using the finite–volume method. Computations are undertaken for different orientations and magnitudes of the imposed magnetic field in circumstances with distinct Rayleigh numbers and the nanoparticles types and volume fractions. The corresponding results are presented in terms of dimensionless distributions of streamlines, isotherms, and heatlines as well as numerical values of the flow strength and the average Nusselt number. Inspection of the results demonstrates that increase in the magnetic field strength deteriorates the heat transfer rate. This effect, however, diminishes with rise in the magnetic field inclination angle.