A sealed storage structure such as a silo having a breather system including a flexible breather bag or equivalent pressurebalancing member. To increase the pressure-balancing capacity of the breather system, a gas cooler assembly is provided. Conduit members connect the cooler assembly to the interior of the silo and to a blower unit to provide a closed gas recirculation path. The cooler and blower are controlled by a thermostat switch within the silo, which switch is set to initiate the recirculation operation at a predetermined maximum temperature and to similarly terminate operation at a predetermined minimum temperature.