Due to its chemical composition, the combustion process of #6 oil produces less moisture than that of natural gas. As a result, #6 oil enjoys an approximate 2.0-2.5% combustion efficiency advantage over natural gas. However, once all of the other losses associated with burning #6 oil are considered, natural gas provides great overall system efficiency. These other losses or costs include:

• Oil Storage
• Heating of stored oil
• Fuel oil additives
• Oil pumping
• Fuel oil atomization
• Soot blowing of boiler tubes
• Additional boiler makeup water
• Additional boiler water treatment chemicals
• Heating of additional makeup water
• Additional maintenance

Dr. Herbert M. Eckerlin form the "Center of Boiler Studies" was hired to conduct the study and provide complete reports on his findings. Dr. Eckerlin tested 26 boilers across the country over a two year period. During that time, he was able to identify the following additional costs which are related to the combustion of #6 oil. These factors were then used to determine the "bottom line" efficiencies of both #6 oil and natural gas.

• Oil Storage
  Since #6 oil is typically used in large commercial and industrial boilers, the storage capability needs to be adequate to maintain a reasonable supply of oil to the boiler. This generally means large storage tanks which are kept as full as possible to minimize the accumulation of moisture build up from condensate. Maintaining this inventory ties up monies which could be used for other business opportunities.
• Oil Heating
  Residual oil, as #6 is often called, is thick fluid which needs to be heated before its viscosity is reduced to the point where it can be pumped. This is generally accomplished through a steam to oil heat exchanger or electric heating elements within the storage tank. In the case of the heat exchanger, the steam condensate is generally dumped to drain rather than returned to the boiler. This is done to prevent contamination of the water in the boiler system should the heat exchanger develop a leak.
• Oil Pumping
  Residual oil needs to be pumped not only from the storage tank to the burner, but is also continually circulated within the tank in order to maintain a consistent viscosity and keep the additives mixed. Electricity is used to operate this pump.
• Oil Additives
  Residual oil contains sulfur and vanadium, both of which create numerous problems for boiler operation, primarily corrosion. Corrosion can occur in the storage tank and on boiler fireside surfaces. Oil treatment chemicals are used to reduce harmful effects of the oil on the equipment.
• Oil Atomization
  Residual oil cannot be burned in the form that it is delivered to the burner. It must be atomized into tiny droplets and sprayed out to form a flame pattern. Atomization can be accomplished through the use of either steam or compressed air.
• Soot Blowing
  When #6 oil is burned it produces a certain amount of carbon ash which is deposited on the fireside surface of the boiler. This soot acts as an insulation and reduced the efficiency of heat transfer from the flame to the boiler water. Unless this soot is removed, the overall efficiency of the boiler will continue to deteriorate. Soot blowing, which is nothing more than steam cleaning or blowing soot from the surfaces with compressed air, is required on a daily basis in order to keep the fireside surfaces relatively clean. Some of the smaller residual oil fired boilers which are not equipped with soot blowers actually switch over to natural gas to help burnoff some of the soot before going back to oil. This does not eliminate the need to manually brush out the boiler tubes, as boiler efficiencies continue to degrade when burning oil.
• Additional Makeup Water
  When steam is used for oil tank heating, atomization and soot blowing, it is lost to drain or atmosphere. Fresh makeup water must then be introduced into the boiler to maintain a safe water level.
• Water Treatment Chemicals
  When fresh fresh makeup water is introduces to a boiler, water treatment chemicals have to be added to maintain desired water conditions.
• Heating Additional Makeup Water
  There are two reasons for heating makeup water. The first and most obvious is that the water needs to be heated near the temperature of the boiler to eliminate the possibility of boiler damage from thermal shock when the water is introduced. The other reason is to remove the oxygen in the water to prevent corrosion within the boiler.
• Additional Maintenance
  Perhaps the single highest additional cost experienced while burning residual oil is the cost of additional maintenance. Since oil requires considerable support equipment such as storage tanks, pumps, soot blowers and heat exchangers, there naturally is more effort required to maintain these systems. A boiler plant which uses residual oil generally will require additional personnel to operate the plant. Even if the number of boiler plant personnel is identical, the personnel in the plant which uses residual oil are kept busy maintaining the oil firing support systems. As a result, less attention is paid to routine boiler maintenance such as repairing or replacing steam traps. This neglect tends to reduce the overall operating efficiency of the boiler plant and further raises the cost of burning #6 oil.

Dr. Eckerlin's analysis determined that the "bottom line" efficiency of natural gas fired boilers is 2.7% higher than residual oil boilers. Therefore, this average can be used as a guide to help get a better understanding of the true cost of burning residual oil.