Boiler efficiency is -
1
\(\frac{\text{Mass of Steam}}{\text{Mass of Fuel}}\)
2
\(\frac{\text{Energy of Steam}}{\text{Energy of Fuel}}\)
3
\(\frac{\text{Mass of Steam} \times \text{Temp. of Steam}}{\text{Calorific Value of Fuel}}\)
4
\(\frac{\text{Energy of Fuel} - \text{Energy of Steam}}{\text{Energy of Fuel}}\)