We present a synthesis of recent results on thermal heat conductivity in nano-composites and nano-structures. The model is a mixt of the Effective Medium Approximation (EMA) and Extended Irreversible Thermodynamics (EXIT). The latter is particularly well adapted to the description of small scaled systems and will be used to derive the expression of the thermal conductivity of nanoparticles. The model is applied to spherical, cylindrical (nanowires) and porous nanoparticles, respectively, being embedded in host media, like polymeric matrices and semi-conductors. Good agreement is observed with other models, experimental data and Monte-Carlo simulations.