Boiler efficiency measures how effectively a boiler converts fuel energy into useful steam or heat. A higher efficiency means less fuel consumption, lower operating costs, and better plant performance.
Use this calculator to estimate boiler efficiency using the direct method for quick checks, or the indirect method for a detailed heat-loss breakdown.
Based on ASME PTC 4 / BEE simplified methods. Results are estimates for engineering analysis — verify with plant instrumentation and fuel laboratory data.
The direct method compares useful heat transferred to steam with the total heat supplied by the fuel. It is simple, fast, and suitable for routine plant monitoring.
η = [mₛ × (hₛ − h_fw)] / (m_f × GCV) × 100
Worked example: Steam 8,000 kg/hr at 10 kg/cm²(g), feedwater 85°C, coal 1,800 kg/hr, GCV 3,200 kcal/kg → efficiency ≈ 80.56%.
The indirect method calculates efficiency by subtracting all major heat losses from 100%. It provides a more accurate analysis and helps identify where energy is being wasted.
η = 100 − (L₁ + L₂ + L₃ + L₄ + L₅ + L₆ + L₇ + …)
| Loss | Name | Description |
|---|---|---|
| L₁ | Dry flue gas loss | Sensible heat carried away by hot combustion gases. |
| L₂ | Hydrogen in fuel | Latent heat to evaporate water formed from hydrogen combustion. |
| L₃ | Fuel moisture | Latent heat to evaporate inherent moisture in the fuel. |
| L₄ | Air moisture | Latent heat of water vapor in supplied combustion air. |
| L₅ | Incomplete combustion | Energy lost when carbon forms CO instead of CO₂. |
| L₆ | Radiation & convection | Heat lost from boiler outer surfaces. |
| L₇ | Unburnt carbon in ash | Combustible material remaining in fly or bottom ash. |
Worked example: Total losses 13.2% (dry flue gas 6.2%, hydrogen 3.0%, fuel moisture 1.2%, air moisture 0.3%, incomplete combustion 0.4%, radiation 1.5%, unburnt carbon 0.6%) → efficiency = 86.8%.
The indirect method is considered more accurate because it calculates individual heat losses separately and helps identify where energy is wasted. The direct method is faster and better suited for routine monitoring. Regular efficiency tracking improves energy savings, combustion performance, and overall plant reliability.
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