Numerous furnaces and boilers are extensively used in industrial and commercial facilities to generate thermal energy so that small improvements of the furnace thermal efficiency will amount to tremendous reduction of energy consumption and green gas emission. In this research, the furnace flue damper angle is adjusted to lower the pressure in the furnace for reducing the velocity of hot gas rising in the furnace. This allows more time for the heat to be transferred to the thermal flow that improves the furnace overall thermal efficiency. On the other hand, when the damper angle is adjusted from 45 to 39 degrees, the pressure in the furnace rises from -14.7 to -9.3 mmH(2)O, the average fuel volumetric flow rate reduces from 751 to 491 m(3)/h, and the average temperature lowers from 949 to 909 degrees C in the radiation section and from 756 to 798 degrees C in the conventional section. Hence, about 1.7 x 10(6) m(3) of fuel gas consumption can be saved, and 1.9 x 10(3) ton of CO2 emission can be reduced annually. The results confirm that simply by adjusting the flue damper angle of a furnace will achieve significant savings of energy and reduction of carbon dioxide emission. Copyright (C) 2012, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.