The present paper investigates the buoyancy induced flow and heat transfer in a square enclosure filled with Fe3O4/water nanofluid heated by mutually orthogonal heaters and symmetrically cooled by sidewalls under the influence of a strong uniform magnetic field. The nanofluid is experimentally synthesized by two-step method and the different thermophysical properties are measured. These experimentally determined properties are compared with the classical correlations available in the literature. Those correlations are found to underpredict the dynamic viscosity and thermal conductivity of the nanofluid. The error related to the use of the classical correlations is determined and it increases with the volume fraction. Hence, the experimentally determined properties are directly used in the numerical simulation. The governing equations in the form of nondimensional stream function, vorticity, and energy equations containing experimentally determined properties are solved using the finite difference method (FDM). The consequence of different factors like positions of the heaters, varying range of Rayleigh number (103 ≤ Ra ≤ 106), the extremely low volume fraction of nanofluids (0 ≤ φ ≤ 0.0007), and Hartmann number (0 ≤ Ha ≤ 75) on the heat transport is studied and reported. The study explains and analyzes the streamlines and isotherms at different conditions. The results show that the positions of the horizontal and vertical heater have a significant effect on heat transfer and fluid flow inside the enclosure. Furthermore, the increase in Ha enervates the strength of flow and it leads to the deterioration of heat transfer.