Four cases of ventilation in a room driven by an occupant’s heat output are modelled. A localized floor heat source is used to represent the convection heat output of the occupant in all cases, while distributed floor/ceiling/wall sources are used to represent the radiation heat output in the ‘‘ radiation ’’ cases. Results show that the differences between non ‘‘ radiation ’’ and ‘‘ radiation ’’ cases are rather small in terms of the outlet flow rate and the outlet temperature/pollutant concentration. The differences are large in terms of the room average temperature/concentration and the heat/scalar removal efficiency. It indicates that the outlet flow rate and the outlet temperature/pollutant concentration of the ‘‘ radiation ’’ cases can be predicted using the theory of emptying filling box. Finally, the similarity of the vertical temperature structure is found between our ‘‘ radiation ’’ model and the discrete radiation model.