Engineering CalculationBoiler Efficiency Calculator - Direct and Indirect Method
Work out boiler efficiency from steam output and fuel input (direct method), or from the individual heat losses (indirect method), and print a test report.
Open the calculator →Formula
Direct method: η = Q × (hg − hf) / (q × GCV) × 100
Q = steam flow (kg/h), hg = steam enthalpy, hf = feed water enthalpy (kJ/kg), q = fuel (kg/h), GCV in kJ/kg
Worked example
10,000 kg/h saturated steam at 10 bar(g) (hg = 2781.7 kJ/kg), feed water 80 °C (hf = 334.9 kJ/kg), coal 2,000 kg/h with GCV 4,000 kcal/kg
η = 10000 × (2781.7 − 334.9) / (2000 × 16,747) × 100 = 73.1 %
Where engineers use it
- Monthly boiler performance monitoring
- Energy audits
- Comparing fuels and boiler replacement
How to use
- Click Open the calculator. It runs free in your browser, on desktop or phone.
- Enter your values. Units and typical ranges are shown next to each input.
- Read the result and the step-by-step working, then print or add it to your Project BOQ.
Questions
Which method is better?
The direct method is quick; the indirect method shows where the heat is lost (flue gas, moisture, unburnt, radiation) so you know what to fix. Both are in the suite.