A supply fan and an extract fan, at identical settings in identical rooms, do not necessarily have the same effect on the ventilation. For a heated room in which the floor-level vents are larger than the ceiling-level vents, we show that an extract fan provides better ventilation than a supply fan. If the ceiling-level vents are larger, we show that a supply fan is more effective; this for the same, constant fan airflow rate. We investigate the hybrid ventilation of a room in which the, otherwise buoyancy-driven, ventilation is augmented by a forced volume flux, provided by a supply or extract fan. In hybrid ventilation, naturally-occurring and mechanically-imposed pressure differences combine to determine the resulting ventilation airflow. Herein, a mathematical model is developed which enables prediction of: the inflow and outflow volume fluxes; the vertical position of the neutral pressure level; and the steady, uniform temperature, with in a single, isolated room in hybrid ventilation. The physical problem is reduced to a mathematical model with two controlling parameters; namely, the effective vent area ratio, R*, and a ratio of forced and natural volume fluxes, Q_F/Q_N. We demonstrate that the volume flux through an open vent can be controlled remotely, by mechanically imposing the volume flux through an entirely separate vent.