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Energy-Efficiency Enhancing Technologies: Improved Flue Baffle / Forced Draft

Studies, tests and actual usage demonstrate that flue baffles and in particular twisted tape flue baffles can enhance the performance and efficiency of gas water heaters. The flue which extends up the center of the tank in a storage tank type water heater from the gas burners at the bottom, transfers heat by convection and radiation to the tube wall and then by conduction to the stored water. A flue baffle increases the turbulence of flue gases and improves heat transfer to the walls of the flue. The twisted tape flue baffle, an improvement over flat plate baffles, improves both the convective and radiant heat transfer from the flue gases to the water-tube walls. It is estimated that improved flue baffles can increase recovery efficiency (RE) to about 78 - 85%. Improved flue baffles also reduce standby loss by the additional restrictions to airflow.

A consideration with improved flue baffle designs that push RE to the higher limits is venting of the combustion products. Higher REs result in higher flue-loss efficiencies, flue gas condensation and excessive "wet-times" in the chimney, which can lead to corrosion and shortened flue life.