Boiler Efficiency Calculator

Instantly calculate the thermal efficiency of your boiler system using direct or indirect method—ideal for energy audits and mechanical analysis.

Direct Method Calculation
kJ/kg
kJ/kg
Boiler Efficiency (Direct Method)
0.00%

Efficiency = (Output Energy / Input Energy) × 100

Indirect Method Calculation

Boiler Efficiency (Indirect Method)
0.00%

Efficiency = 100% - Total Losses

Loss Breakdown:
Dry Flue Gas Loss:
0%
Moisture Loss:
0%
Unburnt Carbon Loss:
0%
Radiation & Convection Loss:
0%
Miscellaneous Loss:
0%
How To Use This Calculator
Step-by-Step Instructions
  1. Select the calculation method (Direct or Indirect) from the left sidebar.
  2. Enter required data:
    • Direct Method: Fuel consumption, calorific value, steam output, and enthalpy values.
    • Indirect Method: Various heat loss parameters from your boiler system.
  3. The calculator will display results in real-time as you enter values.
  4. Optionally, you can:
    • View the loss breakdown chart (for Indirect Method)
    • Copy results to clipboard
    • Load example values for demonstration
Sample Calculation (Direct Method)
Parameter Value
Fuel Used 100 kg/hr
Calorific Value 42000 kJ/kg
Steam Output 1200 kg/hr
Enthalpy of Steam 2760 kJ/kg
Feedwater Enthalpy 420 kJ/kg
Result ~67.7% Boiler Efficiency
Tips & Best Practices
  • Typical boiler efficiency ranges from 70% to 90% for modern systems.
  • For accurate results, use measured values rather than design specifications.
  • The indirect method helps identify which losses are most significant for potential improvements.
  • Regular efficiency calculations can help track boiler performance over time.
Reference Data
Fuel Calorific Values
Fuel Type Calorific Value (kJ/kg) Calorific Value (kcal/kg) Calorific Value (BTU/lb)
Coal (Bituminous) 30,000 – 35,000 7,170 – 8,360 12,900 – 15,000
Furnace Oil 41,000 – 45,000 9,800 – 10,750 17,600 – 19,300
Natural Gas 48,000 – 52,000 11,470 – 12,420 20,600 – 22,300
Biomass Pellets 14,000 – 18,000 3,350 – 4,300 6,000 – 7,700
Diesel 45,000 – 46,500 10,750 – 11,100 19,300 – 20,000
Typical Steam Enthalpy Values
Pressure (bar) Saturation Temperature (°C) Feedwater Enthalpy (hf, kJ/kg) Steam Enthalpy (hg, kJ/kg)
1 99.6 417 2,675
5 151.8 640 2,748
10 179.9 762 2,778
15 198.3 844 2,792
20 212.4 908 2,799
Formulas
Direct Method:

Efficiency(%) = (Output Energy / Input Energy) × 100

Input Energy = Fuel Consumed × Calorific Value

Output Energy = Steam Output × (Enthalpy of Steam - Feedwater Enthalpy)

Indirect Method:

Efficiency(%) = 100 - Total Heat Losses

Typical losses include:

  • Dry flue gas loss
  • Moisture in fuel loss
  • Hydrogen in fuel loss
  • Radiation & convection losses
  • Unburnt carbon loss