Conjugate natural convection heat transfer in a two-dimensional, air-filled enclosure containing discrete internal heat sources and an internal baffle is examined. The enclosure formed of finite conductive walls is designed to simulate the behavior of an experimental window calorimeter in order to correct for losses from the calorimeter. The equations are solved using a finite-volume method for a wide range of Rayleigh numbers, internal-external heat source ratios, solid-fluid conductivity ratios and baffle heights. The influences on the heat transfer and the Bow characteristics resulting from the internal heat sources as well as the conductive baffle are discussed. Measurements of temperature distributions in the window calorimeter are also reported. The comparison between numerical predictions and experimental measurements shows that it is inappropriate to specify simple boundary conditions on the window surface of the calorimeter and to neglect the conduction through the baffle, window, and walls. A modified procedure for calculating the temperature distributions on the window surface improves the predicted results and yields good agreement with the measured data.