An oven (10) for the thermal conditioning of preforms made of thermoplastic, is traversed upstream to downstream by an air stream (A) for cooling the preforms and includes successively an air inlet zone (16a) having at least one air inlet port (22a), a zone (16b) for heating the preforms, that includes at least one ventilation module (36) that is able to guide the air stream (A) coming from the inlet zone (16a) to the preforms, an air extraction zone (16c) having at least one air extraction duct (68), characterized in that the air inlet zone (16a) includes a plurality of ventilation modules (36) and at least one air distribution chamber (18), called a plenum (18), which is interposed between the air inlet port (22a) and each of the ventilation modules (36).