COBREX® storage steam water heaters utilize a double-wall, copper-tube, counter-flow heat exchanger to provide moderate to large amounts of domestic hot water from steam. The heat exchanger is external to the tank and provides exceptionally little floor space to remove the exchanger, if necessary. The heat exchanger and tank are connected with factory-assembled piping. Electronic operating control is Modbus connectable to a building automation system. No steam control valve is necessary when the inlet steam pressure is 15 psi or less.