How is efficiency measured in a steam boiler?

Efficiency in a steam boiler is determined by the ratio of useful energy output to energy input. This measurement indicates how effectively the boiler converts the energy from fuel into steam energy that can be used for heating or power generation. A higher efficiency rating means that more of the energy from the fuel is being converted into useful steam energy, resulting in less waste and more cost-effectiveness in operation.

For example, if a boiler inputs a certain amount of fuel energy and produces a specified amount of useful steam energy, comparing these two figures allows us to calculate efficiency. This metric is crucial for evaluating boiler performance and optimizing operational costs.

The other choices do not accurately capture the concept of efficiency. While the amount of steam produced and the amount of fuel consumed are important performance metrics, they don't directly provide a measure of how efficiently the boiler is operating relative to its energy usage. Additionally, the temperature of the steam is a characteristic of the steam itself but does not reflect the boiler's efficiency in terms of energy conversion. Thus, measuring efficiency specifically in terms of energy output versus energy input is the most accurate method.