Utilities
Steam per kilogram of fuel is the number the boiler house can see hourly. Efficiency is the same truth in the units the energy manager wants.
— %
Direct method: heat into steam over heat in fuel
The direct method carries the error of both meters and says nothing about where the losses go — for that, run the indirect (heat loss) method with a flue gas analysis. An efficiency above about 92% on the direct method almost always means a mis-metered fuel or steam flow rather than an exceptional boiler.
Boiler Steam Efficiency & Fuel Ratio Calculator — free, with the formula and a worked example, at Textile School.