Natural convection of a water-based nanofluid consisting Cu nanoparticles in a semi-annulus enclosure subjected to a magnetic field is considered. The inner wall has constant heat flux, the outer wall is maintained at a cold temperature and the other two walls are thermally insulated. The governing equations derived by considering the effect of magnetic field are solved numerically using the dual reciprocity boundary method (DRBEM) with constant elements. The boundary only nature of the dual reciprocity method results in considerably small computational cost in obtaining the solution. The simulations focus on the effects of the Rayleigh number, the Hartmann number, the nanoparticle volume fraction, and the inclination angles of the enclosure and the magnetic field on the flow and heat transfer characteristics. The results show that the convection and the average Nusselt number ((Nu) over bar) decrease with an increase in the strength of the magnetic field whereas they increase by increasing the Rayleigh number. Furthermore, an increase in Hartmann number accelerates the rate of decrease in (Nu) over bar as inclination angles decrease. Thus, the inclined magnetic field and the inclination angle of the enclosure can be used as control parameters for enhancing the heat transfer convection and flow behavior in an enclosure. (C) 2016 Elsevier Ltd. All rights reserved.