Direct method
Boiler efficiency is the heat taken up by the steam divided by the heat in the fuel. Direct method ฮท = [Steam ร (hs โ hw)] รท [Fuel ร GCV]. Enthalpy of steam comes from steam tables. Feed-water enthalpy depends on feed temperature. A marine auxiliary boiler often sits around 80โ90% if the uptake is clean and the burner is set correctly.
How this calculator works
Enter steam kg/h, an enthalpy rise (default 2400 kJ/kg if you do not have tables to hand), fuel kg/h and GCV. Efficiency is shown as a percentage. This ignores blow-down, radiation and unburnt losses as separate items. Indirect (heat-loss) method is more accurate for a survey but needs flue-gas analysis.
Who should use it
Useful for engineers watching fuel versus steam. Use steam tables and the boiler manual for an official test.