A mechanical deaerator provides an alternative to oxygen scavengers and other chemicals for oxygen removal in hot water and steam systems. A Dif-Jet gas injector can be used for batch production of deaerated water in storage tanks. The device efficiently injects and mixes nitrogen gas into a pressurized water pipe before discharging the gas into a circulating tank of water. The nitrogen forces the oxygen out of the water without requiring a vacuum pump, heat or other device. The oxygen is vented out of the top of the tank automatically. The company tested the system using a 500-gal closed-head polyethylene tank with a single gas injector. Paired with a nitrogen generator, this system can provide a continuous stream of deaerated water.