Abstract: A deaerator for deaerating the feed water to a steam generator, the deaerator comprising a single enclosure (1) including a deaerating device, said enclosure being divided into two longitudinal zones (A, B) with a first one of said zones (A) corresponding to the location of said deaerating device, said first zone (A) having a cross-section which is larger in area than the cross-section of the other or second one of said zones (B), the center of gravity (G1) of said cross-section of said first zone being higher than the center of gravity (G2) of the cross-seciton of said second zone, the top portion of said first zone being provided with escape orifices (15) for the incondensable, nozzles (17) for spraying the water to be deaerated and reheated, and a reheating steam inlet (14) leading to a steam distribution chest (16) for distributing steam into longitudinal passages (28, 29) situated in an elongatge box (24) suspended from the walls of said first zone (A) of the enclosure, said box (24) being fed in a centr