Excess air is very important factor to increase combustion efficiency, and decrease pollutants emission. In this thesis, we provide that development plans and environmental conservation go in one direction, where we can decrease environmental pollution with economic benefits in the same time. By monitoring the emissions from four stacks (two boilers in petrochemical sector and two boilers in food sector) all are working using natural gas as a fuel. Changing in excess air to increase the combustion efficiency, which means fuel saving, and decrease pollutants concentration. There is a relationship between the cost, combustion, stack heat loss, fuel saving and environment.       By using portable stack gas analyzer combustion efficiency and emitted pollutants through the stacks were measured before and after maintenance and changing air ratio mixed with the fuel. In boiler 1 of the petrochemical sector CO changed from 2222 mg/m³ to 21 mg/m³. In boiler two CO changed from 4695.3 mg/m³ to 5.5 mg/m³. Efficiency of boiler1 and 2 improved from 75.5% to 92.1 %, and from 71.5 to 93.1 respectively. In boiler 1 of food sector CO changed from 2200 mg/m³ to 45 mg/m³. In boiler 2 CO changed from 1900 mg/m³ to 59 mg/m³. Efficiency of boiler1 and 2 improved from 69.8 % to 91.4 %, and from 76.5 to 91.1 respectively. The cost reduction per year in petrochemical sector were 8469.1 $ in boiler 1 and 11692.8 $ in boiler 2, while 11624.4 $ and 12168.2 $ in boiler 1 and 2 of food sector.