A numerical study is performed to examine the influence of a non-uniform magnetic field on the thermo-hydraulic behaviour of a ferrofluid. The analysis is done in the context of a differentially heated semi-circular annulus where a magnetic dipole with its distinct location and dipole strength is used to obtain different configurations. The field variables are computed by solving the coupled set of flow equations, energy equations and the Maxwell’s magneto-statics equations. A detailed description is provided on the flow and thermal response after observing different parameters at both global and local scale. Comparison of streamlines and isotherms with a reference case of natural convection concludes that the recirculation zones are responsible for the increased velocity and heat transfer magnitudes. Another key finding of the present work is about the possibility to locally improve the thermal performance of heat exchangers at any desired position along the circumference.