This paper describes the first application of 3D density reconstruction from a limited number of background oriented schlieren (BOS) images in a large research-type low speed wind tunnel. The tested flow is an ad hoc co-flowing hot jet generated at the wingtip of a simplified airfoil. Ray deviation maps captured by 12 synchronized cameras are combined to reconstruct the three dimensional density field of the jet, in the line of the direct 3D BOS technique described in Nicolas et al (2016 Exp. Fluids 57 1–21). A comparison with thermocouple sampling shows consistent results and highlights the efficiency of this new method for thermal measurement of a low speed convective flow. Finally, we underline the new possibilities for fluid dynamic characterization offered by combining stereo particle image velocimetry and 3D BOS measurements.