These Feed Water Heaters are said to provide a more energy efficient and cost effective solution, compared to traditional economizers, for process and other manufacturing applications. The heaters maximize exhaust stack heat recovery by recycling waste heat through a single-stage, two-stage, condensing economizer, or on-demand system. These can increase operating efficiency up to 90% and lower overall fuel requirements and energy costs. Burning less fuel also results in reduced emissions, contributing to a cleaner environment. The units also heat low-temperature make-up or process water as well as deaerated feedwater. The greater the input temperature difference, the higher the heat recovery.