PURPOSE: To release a gas in hot water by providing a flow regulating mechanism to keep a sufficient space in the titled deaerator, furnishing a nozzle to atomize hot water to be fed into the space and providing a filter for collecting fine bubbles before a supply hot water outlet.

CONSTITUTION: Hot water from an inlet 2 is atomized 4 by a nozzle 3 equipped with an opening and closing mechanism and discharged into a space in the main body 1. The water level in the space is kept at a fixed level 6 by a flow regulator 5 and regulated not to exceed the high level 7. The pressure in the space is regulated at a value of about 0kg/cm2 atmospheric pressure through a deaeration pipe 10. Since 5ppm excess oxygen remains in hot water at 55°C, the excess oxygen is rapidly discharged to the outside from the atomized hot water. The fine bubbles remaining in hot water below the fixed water level 6 are collected by a filter 11 and discharged from a suction port 8 to a circulating pipeline through a discharge port 9. Consequently, gaseous oxygen, chlorine, etc., contained in hot water is discharged to the outside and the corrosion of metal is prevented.