Vertical oven (51, 61) for drying painted objects, mainly flat parts both made of wood and its derivatives and plastics, metal, fibrocement and suchlike, the oven comprising: at least two vertical transit chambers (21, 23); a plurality of trays (41, 42, 43, 44, 45, 46,...) for supporting the said painted objects, the said plurality of trays being arranged in a stack (31, 32; 81, 82, 83, 84) of superimposed trays within each of the said at least two transit chambers (21, 23); motorized tray conveyor units for displacing the trays along a path comprising at least an ascending portion inside a first of the at least two transit chambers, a lateral shifting portion from the said first transit chamber to a second of the said at least two transit chambers and a descending portion inside the said second transit chamber; an input and/or output port being provided at the bottom of the said at least two transit chambers at which there is provided alternatively or in combination a loading unit, an unloading unit of the dried parts from the trays and a conveyor unit for shifting the trays from the lower and of the second transit chamber to the lower end of the first chamber for recirculating the trays along the said path inside the at least two transit chambers, the trays (41, 42, 43, 44, 45, 46,...) having a predefined distance "d" one from the other in the stacks inside the at least two chambers (21, 23), characterized in that the oven includes at least one further parking chamber; the said parking chamber being destined for temporarily parking one or more trays (42, 44, 43) in a stack of parked superimposed trays; transferring devices for withdrawing trays from the stack of a first or a second transit chamber of the said at least two transit chambers and feed the said trays to the at least one parking chamber or vice versa for re-insertion of the trays in the stack of the said first or said second transit chamber of the said at least two transit chambers, a control unit being provided controlling the transferring devices for operating the withdrawal of every second tray in a stack and the parking of the said trays in the at least further parking chamber thus doubling the distance d between the trays in the stacks (31, 32; 81, 82, 83, 84), which becomes 2d, in at least one transit chamber of the at least two transit chambers (21, 23). at least two vertical transit chambers (21, 23); a plurality of trays (41, 42, 43, 44, 45, 46,...) for supporting the said painted objects, the said plurality of trays being arranged in a stack (31, 32; 81, 82, 83, 84) of superimposed trays within each of the said at least two transit chambers (21, 23); motorized tray conveyor units for displacing the trays along a path comprising at least an ascending portion inside a first of the at least two transit chambers, a lateral shifting portion from the said first transit chamber to a second of the said at least two transit chambers and a descending portion inside the said second transit chamber; an input and/or output port being provided at the bottom of the said at least two transit chambers at which there is provided alternatively or in combination a loading unit, an unloading unit of the dried parts from the trays and a conveyor unit for shifting the trays from the lower and of the second transit chamber to the lower end of the first chamber for recirculating the trays along the said path inside the at least two transit chambers, the trays (41, 42, 43, 44, 45, 46,...) having a predefined distance "d" one from the other in the stacks inside the at least two chambers (21, 23), characterized in that the oven includes at least one further parking chamber; the said parking chamber being destined for temporarily parking one or more trays (42, 44, 43) in a stack of parked superimposed trays; transferring devices for withdrawing trays from the stack of a first or a second transit chamber of the said at least two transit chambers and feed the said trays to the at least one parking chamber or vice versa for re-insertion of the trays in the stack of the said first or said second transit chamber of the said at least two transit chambers, a control unit being provided controlling the transferring devices for operating the withdrawal of every second tray in a stack and the parking of the said trays in the at least further parking chamber thus doubling the distance d between the trays in the stacks (31, 32; 81, 82, 83, 84), which becomes 2d, in at least one transit chamber of the at least two transit chambers (21, 23).