A ventilation apparatus for ventilating a building. The ventilation apparatus comprises a casing comprising: a cavity for housing a removable heat-exchange cartridge； a service door providing access to the cavity； a primary and secondary pathways fluidly connecting the inside of the building to the outside of the building, wherein the primary pathway and the secondary pathway cross the cavity along about perpendicular axes； a primary ventilator for forcing an airflow in the building through the primary pathway； and a controllable secondary ventilator for forcing a controllable airflow through the secondary pathway. The ventilation apparatus, when the casing houses the heat-exchange cartridge, has the primary ventilator forcing an inflow of air through the primary pathway, and (ii) the controllable second ventilator for controllably forcing either an outflow or an inflow of air through the secondary pathway. The ventilation apparatus, without heat-exchange cartridge, has only inflow(s) forced through the pathway(s).
