A 3mm thick soot deposition on the heat transfer surface can increase fuel consumption by about 2.5%. It is recommended to clean the fireside to maintain optimum efficiencies.

Soot is a general term that refers to impure carbon particles that result from the incomplete combustion of a fuel. Soot buildup on the fireside of the boiler surfaces inhibits heat transfer. When less heat is transferred to the boiler water, more heat remains in the flue gases and is rejected up the stack. A layer of soot only 3mm in thickness reduces boiler efficiency by an estimated 2.5%.

Fuel oil combustion deposits predominately consist of soft black soot. For small fire tube boilers, these deposits are easily removed by manual brushing. Lower grade fuel oils cause more serious fire-side deposits. Solid fuels such as coal and wood wastes produce deposits that contain ash-based slag. If not removed immediately, these deposits can become sintered or melt into a difficult to remove glass-like insulating layer. Large water-tube boiler deposits can be removed with a blast of high-pressure water. With low-quality fuels, soot blowing may be necessary as frequently as once per shift. Thus by cleaning the boiler heat transfer surfaces regularly, the boiler efficiency can be maintained at the optimum level. This will result in reduced fuel consumption and thus lower fuel bills.