In this work, the hybrid immersed boundary method is extended with immersed boundary conditions for the temperature field. The method is used to couple the flow solver with a shell heat transfer solver. The coupling back to the shell is handled by a heat source, calculated from Fourier's law. Natural convection in a square cavity with and without a hot circular cylinder, and free air cooling of an electrically heated plate are studied. For all cases an excellent agreement with numerical and experimental data is obtained. The proposed method is very well suited for many industrial applications involving natural convection. (C) 2012 Elsevier Ltd. All rights reserved.