Thermal Efficiency
A boiler’s thermal efficiency is calculated using the below equation. Multiplying the output of the equation by 100 gives the thermal efficiency value in percentage (%).
Thermal efficiency is not calculated as: (energy out / energy in). Thermal efficiency indicates how much of the heat generated by combustion is transferred to the water; it does not indicate how much of a boiler fuel’s chemical energy was transferred to the water. Low thermal efficiency values often indicate heat transfer problems such as dirt or scale on the heat transfer surfaces.
A boiler with high thermal efficiency is desired because it consumes less fuel and thus saves money, this can be better understood when reading the below examples.
Example 1
A boiler thermal efficiency of 50% indicates that half of the thermal energy (heat) generated by the combustion process was not transferred to the water.
Example 2
A boiler thermal efficiency of 100% indicates that all of the thermal energy (heat) generated by the combustion process was transferred to the water.
Most industrial boilers should achieve a thermal efficiency of 80% or more, but this depends heavily upon the boiler’s design, type of fuel burnt, age of the boiler and its condition.