Boiler Efficiency Calculator

Work out boiler efficiency instantly with clear inputs, formula shown and shareable results.

About Boiler Efficiency Calculator

The direct or input-output method compares the heat absorbed by the steam with the heat released by the fuel. Steam flow times enthalpy rise is the useful output; fuel flow times gross calorific value is the input. The gap is the sum of stack, blowdown, radiation and unburnt losses.

Formula

Direct method efficiency

η = steam flow x enthalpy rise / (fuel flow x GCV) x 100

Worked example

With the default values below, Boiler Efficiency Calculator returns Boiler efficiency of 75.19%. Change any input above and every figure here is recalculated in your browser.

Inputs used

Steam generatedminimum 1 lb/h: 5,000 lb/h
Enthalpy rise, feedwater to steamminimum 1 BTU/lb: 1,000 BTU/lb
Fuel consumptionminimum 0.1 lb/h: 350 lb/h
Fuel gross calorific valueminimum 100 BTU/lb: 19,000 BTU/lb

Results

Boiler efficiency: 75.19% %
Useful heat output: 5,000,000 BTU/h
Fuel heat input: 6,650,000 BTU/h
Total losses: 1,650,000 BTU/h

Step by step

1Values used
2Direct method efficiency
3Boiler efficiency= 75.19 %
4Useful heat output= 5,000,000 BTU/h
5Fuel heat input= 6,650,000 BTU/h
6Total losses= 1,650,000 BTU/h

Assumptions and limits

The result is derived only from the 4 inputs listed above. Anything not among them is not part of the calculation.
In particular, this calculator does not take inflation, tax or compounding frequency into account.
Figures are rounded for display to 2 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.

How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.

Frequently Asked Questions

How is the Boiler Efficiency figure worked out?

η = steam flow x enthalpy rise / (fuel flow x GCV) x 100. The direct or input-output method compares the heat absorbed by the steam with the heat released by the fuel.

When is the indirect method better?

When fuel or steam metering is unreliable. The indirect method adds up measurable losses instead, which also shows which loss to attack.

What values do I need to enter?

This calculator takes 4 inputs: Steam generated, Enthalpy rise, feedwater to steam, Fuel consumption, Fuel gross calorific value. The pre-filled defaults are a realistic worked example — replace them with your own site or project figures.