Use the correct efficiency term

Term	What it measures	Primary limitation
Fuel-to-steam	Useful steam energy divided by fuel input, including boiler radiation and convection losses.	Does not represent cycling, standby, or actual load profile.
In-service	Overall performance across operating cycles, low load, standby, nights, and weekends.	Requires a defined operating model or field data.
Combustion	Burner effectiveness in completely burning fuel.	Does not measure heat-exchanger or casing losses.
Thermal	Heat-transfer effectiveness of the heat exchanger.	Excludes radiation and convection losses.
Boiler efficiency	Ambiguous unless the manufacturer defines the basis.	Can lead to invalid comparisons.

Comparison method

Define the operating profile and steam load distribution.
Use fuel-to-steam efficiency for controlled equipment comparisons.
Use in-service efficiency for economic comparisons.
Include cycling, standby, radiation, purge, blowdown, feedwater temperature, and condensate return assumptions.
Document the calculation method and source of every input.