A thermal conditioning device for thermally conditioning preforms, comprising a heating module provided with an enclosure with a transport volume for said preforms; a heating means and a cooling means that are oriented toward the volume; a control means for controlling said heating and cooling means; said cooling means comprising a circulating means for circulating a flow of air with a nominal flow rate determined by said control means; a channel between said circulating means and said enclosure and leading toward said volume; wherein it comprises, along said channel, a measuring means for measuring the actual flow rate and an adjusting means for adjusting said nominal flow rate with respect to said actual flow rate, by controlling the control means. The invention also relates to a corresponding thermal conditioning method.