The two-dimensional turbulent airflow generated by two non-isothermal plane wall jets in a compartment is numerically investigated over a wide range of supply ah-flow rates. The low-Reynolds-number turbulence model of Nagano and Hishida, assembled in a finite-volume-based numerical code, is used after a previous validation study involving several other formulations of the k-epsilon model. The results of an extensive parametric study are reported and discussed, and conclusions are drawn about the relative influences of the room aspect ratio, the jet inlet sections, the temperature of the walls and the ratio of ventilation-to-heating airflow rates on the flow structure and the maximum velocity in the return flow. Evidence is provided that the common requirements of ventilation rate in non-industrial buildings imply airflows that lie within a mixed convection regime, where deep changes of the flow pattern can occur. Attention is given to the parametric conditions associated with flow reversal, a situation that can seriously compromise thermal comfort. In fact, the maximum velocity in the occupied zone may then double for the same ventilation rate.