Natural convection of a nanofluid in a square cavity filled with a porous matrix is numerically investigated using a meshless technique. The Darcy-Brinkman and the energy transport equations are used to describe the nanofluid flow and the heat transfer process in the porous medium as these are generated by heating one of the cavity walls. The role of the nanofluid properties in the cooling performance of the medium and in the relevant heat process is thoroughly investigated. Numerical results are obtained for the stream function, the temperature profile, and the Nusselt number over a wide range of dimensionless quantities (Rayleigh number between 105 and 107, Darcy number between 10-5 and 10-3). The effect of the porous medium in the cooling efficiency of the nanofluidic system is also discussed. Alternative expressions are suggested for the estimation of the effective conductivity and the thermal expansion coefficient of the nanofluid and their effects on the heat transfer problem are investigated. Excellent agreement with experimental data and trends as well as with previously published numerical results for less complicated systems was found.