Horizontal atmospheric steam deaerator, made of steel, externally rustproof painted, to be combined with steam generators for degassing feed water. The degassing of feed water is important to minimise the presence of carbon dioxide and oxygen to avoid corrosive phenomena within the steam generators and the plant. Mineral wool insulation and external aluminium plate finish. Equipped with: thermoregulator unit complete with valves and filters, water supply unit, automatic level regulator with probes, purging unit and control panel.