Define 'thermal efficiency' in the context of boiler systems.

Thermal efficiency is a crucial parameter in boiler systems, reflecting how effectively the system converts the energy input into useful energy output. It is defined as the ratio of useful energy output to the total energy input, taking into consideration any heat losses that occur during the process.

In the context of a boiler, this means that thermal efficiency gauges the effectiveness of the boiler in generating steam or heating water compared to the amount of energy supplied through fuel. Ideally, a high thermal efficiency indicates that the system is well-designed and well-maintained, minimizing waste and maximizing output.

Understanding thermal efficiency is essential for determining the overall performance of boiler systems, as higher efficiency can lead to cost savings and reduced environmental impacts due to decreased fuel consumption. In contrast to other options, which either misinterpret thermal efficiency or refer to different concepts, this option accurately captures the essence of the measure in a boiler context.