Advanced Boiler Efficiency Check Calculator

Calculator Inputs

Large screens show three columns, medium screens show two, and mobile shows one.

Reset to defaults

Fuel type

Changing fuel fills suggested engineering defaults.

Steam flow (kg/h)

Total steam generation rate.

Steam enthalpy (kJ/kg)

Use your steam table or instrument reading.

Feedwater temperature (°C)

Feedwater enthalpy is approximated as 4.186 × temperature.

Fuel rate (kg/h or equivalent)

Use a consistent basis with GCV.

Fuel GCV (kJ/kg)

Gross calorific value on the same fuel basis.

Stack temperature (°C)

Higher stack temperature usually raises flue losses.

Ambient temperature (°C)

Used for loss temperature difference.

Excess air (%)

Extra combustion air beyond stoichiometric requirement.

Hydrogen in fuel (%)

Hydrogen forms water vapor and latent loss.

Fuel moisture (%)

Moist fuel lowers usable heat release.

Ambient humidity ratio (kg/kg dry air)

Typical dry air values often range near 0.008 to 0.020.

Dry flue gas factor (kg/kg fuel)

Use lab data when available.

Theoretical air factor (kg/kg fuel)

Needed to estimate moisture carried by air.

Flue gas specific heat, Cp (kJ/kg·K)

Common approximations range near 1.0.

Blowdown rate (%)

Percent of steam generation sent to blowdown.

Blowdown temperature (°C)

Used for blowdown heat loss estimate.

Radiation and convection loss (%)

Often estimated from boiler size and insulation quality.

Unburned fuel loss (%)

Applicable when incomplete combustion is present.

Example Data Table

Use this sample operating case to understand the expected input pattern.

Fuel	Steam flow	Steam enthalpy	Feedwater temp	Fuel rate	GCV	Stack temp	Excess air	Direct efficiency	Indirect efficiency
Natural Gas	10,000 kg/h	2,778 kJ/kg	90 °C	600 kg/h	50,000 kJ/kg	220 °C	15%	≈ 80.03%	≈ 77.72%
Diesel Oil	8,500 kg/h	2,760 kJ/kg	105 °C	500 kg/h	42,700 kJ/kg	240 °C	20%	Depends on inputs	Depends on losses

Formula Used

Direct efficiency:

Boiler Efficiency (%) = [Steam Flow × (Steam Enthalpy − Feedwater Enthalpy)] ÷ [Fuel Rate × GCV] × 100

Feedwater enthalpy approximation:

Feedwater Enthalpy (kJ/kg) ≈ 4.186 × Feedwater Temperature (°C)

Indirect efficiency:

Boiler Efficiency (%) = 100 − (Dry Flue Loss + Hydrogen Loss + Fuel Moisture Loss + Air Moisture Loss + Blowdown Loss + Radiation Loss + Unburned Loss)

Dry flue gas loss:

Dry Flue Loss (%) = [Dry Flue Gas Factor × Cp × (Stack Temp − Ambient Temp) × (1 + Excess Air)] ÷ GCV × 100

This calculator is an engineering estimate. Replace default factors with measured fuel and flue-gas data whenever available.

How to Use This Calculator

Choose the fuel type and apply defaults if needed.
Enter steam flow, steam enthalpy, and feedwater temperature.
Provide fuel rate and gross calorific value.
Add stack temperature, ambient temperature, and excess air.
Fill moisture, hydrogen, blowdown, and miscellaneous losses.
Press Check Boiler Efficiency.
Review the summary cards, graph, and loss table.
Export the result with CSV or PDF download buttons.

Frequently Asked Questions

1) What does direct efficiency measure?

Direct efficiency measures how much fuel energy becomes useful steam-side energy. It uses steam output, steam enthalpy, feedwater enthalpy, fuel rate, and fuel calorific value.

2) Why is indirect efficiency also useful?

Indirect efficiency highlights where energy is lost. It is valuable for troubleshooting because it separates flue-gas, moisture, blowdown, radiation, and unburned fuel losses.

3) Why can direct and indirect results differ?

The gap usually comes from measurement uncertainty, estimated factors, poor sensor calibration, or inconsistent fuel-property data. Small differences are normal, but large gaps deserve investigation.

4) How do I find steam enthalpy?

Use steam tables, a process simulator, or instrumentation linked to boiler pressure and temperature. Enter the enthalpy on the same operating condition as the steam flow value.

5) What if I do not know dry flue gas factor?

Start with the suggested default for your fuel type, then replace it with measured or laboratory values later. Better flue data gives better indirect efficiency estimates.

6) Does blowdown always reduce efficiency?

Yes, excessive blowdown removes hot water from the boiler. Some blowdown is necessary for water-quality control, but unnecessary blowdown increases energy and makeup-water losses.

7) Which input has the strongest effect on losses?

Stack temperature, excess air, hydrogen content, and moisture often influence results the most. Their effect depends on fuel type, firing quality, and operating load.

8) Can this tool replace a full combustion audit?

No. It is a practical screening and review tool. A full audit should include calibrated analyzers, fuel testing, steam measurements, and combustion tuning checks.