This Code provides rules and test procedures that are to be used to determine the performance of deaerators with regard to residual dissolved oxygen in the deaerated water and terminal temperature difference (TTD), if any, between the deaerated water and the saturated steam temperature corresponding to the pressure in the steam zone adjacent to the interface between the steam and the collected deaerated water. This Code applies to deaerating heaters and deaerators equipped with either shell-and-tube or direct contact, vent-condensing sections. It describes the test method for the determination of dissolved oxygen in water for deaerating equipment at concentrations up to 75 鎔/L (ppb).