Abstract: The housing is heated or cooled to adjust its diameter and, in particular, the play between the tips of the rotor blades and the housing. The apparatus consists of networks of tubes (1) covering complementary portions of the circumference of the housing and consisting of a pair of distributors (3) and parallel tubes (2) between said distributors, said tubes (2) being alternately connected to one or other of the distributors and provided with apertures to blow the gas onto the housing. The counter-flow circulation in the tubes (2) makes it possible to supply both gas that has been greatly heated by traveling a considerable distance through the tubes (2) and cooler gas that has traveled less far in other tubes (2) to any point on the housing, thereby balancing out the heat applied to every portion of the housing.