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Economizers are basically heat exchangers. They transfer the heat content of the flue gases to another medium (boiler-feed or makeup water). They increase the overall efficiency of the system.
Depending upon the type of economizer you are using, you may see a 2-5% increase or a 10-15% (condensing boiler) increase in the efficiency of your system.
Every time hot flue gases pass through a set of tubes before making a turn, a “pass” is said to be made. In our three-pass design, the gases first pass through the flame tube –this is the first pass. After that, they pass through the smoke tubes –this is the second pass. And in the end, the gasses take a turn and pass through another set of smoke tubes –this is the third pass. This design ensures maximized heat transfer.
There are two primary fire tube boiler designs: “Wetback” and “Dryback.” Wetback design has water in the rear wall of the boiler, whereas the dryback design has refractory lining the rear wall.