Natural convection of gas in a differentially heated 2Dcavity partially filled with a stack of horizontal conductingplates is investigated numerically. This specific situationmay be encountered in thermoacoustic wave generators.The thin left and right fluid layers around the stack induceconvective movements which strongly affect thetemperature distribution. In order to predict the actualtemperature field for practical applications, the results areanalysed in terms of convection Darcy type flow througha strongly anisotropic porous medium.