A ventilation assembly is defined comprising a fan located in the top of a drying chamber or furnace and which recirculates gases at high temperatures and/or humidity; a drive shaft with its mounts or bearings, on which is mounted the fan, and a separation chamber which houses the shaft bearings and separates said bearings from the inside of the drying chamber or furnace. The separation chamber is open to the external environment and is sized such that a person may enter it to perform maintenance of the shaft bearings without the need to enter the dryer or furnace. The ventilation assembly may further include the pre-assembly in the factory of the engine, its transmission system and/or one or more air renewal vents. Furthermore, the assembly can be complemented with trusses to further facilitate installation on the walls of the dryer or furnace.