Boiler Efficiency Calculator
Boiler Efficiency: Efficiency = useful heat output ÷ fuel energy input × 100 (direct method). Methodology stated, your own inputs only.
In short
Boiler Efficiency: Efficiency = useful heat output ÷ fuel energy input × 100 (direct method). Methodology stated, your own inputs only.
Formula: Efficiency = useful heat output ÷ fuel energy input × 100 (direct method).
What this calculator does
Boiler Efficiency: Efficiency = useful heat output ÷ fuel energy input × 100 (direct method). Methodology stated, your own inputs only. Worked example, questions and limitations included.
Use it to turn Useful heat output (steam or hot water), Fuel energy input (fuel used × heating value, same unit) into a checked result you can compare, copy, or rerun with different assumptions.
The page shows the formula, a numeric worked example, and the assumptions that affect this energy calculation.
Inputs and what they mean
- Useful heat output (steam or hot water)
- — number value.
- Fuel energy input (fuel used × heating value, same unit)
- — number value.
How to use it
- Enter each value in the unit shown next to the box (use the unit converter first if your numbers are in other units).
- Check the breakdown to see every intermediate step.
- Read the limitations before relying on the result.
Formula
Methodology: input–output (direct) method described in the U.S. DOE steam system sourcebook.
State whether the heating value is higher (HHV) or lower (LHV); results differ by several points.
Measure output and input over the same period.
Efficiency = useful heat output ÷ fuel energy input × 100 (direct method).
Inputs used: Useful heat output (steam or hot water), Fuel energy input (fuel used × heating value, same unit).
Worked example
A test period
- 850 ÷ 1,000 = 85.00%.
Reading the result
The headline figure is the main answer. Any breakdown underneath shows the parts that make it up, so you can check the working and see what changes when you adjust an input.
Limitations and assumptions
- Accuracy depends on metering of fuel and output.
- Single period; part-load behaviour not shown.
- Results are estimates built only from the figures you enter. No electricity, fuel or gas price, equipment efficiency or benchmark is built in — tariffs vary by supplier, region and time, and equipment data must come from the manufacturer. Designs and installations must be checked by a qualified professional.
- The result depends on the values you enter for this boiler efficiency calculator; it does not supply missing rates, rules, prices, dates, or assumptions for you.
Reference: U.S. Department of Energy
Last reviewed:
Common questions
HHV or LHV?
Either, but say which. LHV-based efficiency reads higher than HHV-based.
Direct or indirect method?
This is the direct method. The indirect (heat-loss) method adds up individual losses instead.
Is a typical efficiency built in?
No. Efficiency depends on boiler type, load and fuel; it is always calculated from your figures.
How do I use the Boiler Efficiency Calculator?
Enter the required values for Useful heat output (steam or hot water), Fuel energy input (fuel used × heating value, same unit). The calculator applies the formula on this page and shows the main result with any supporting breakdown so you can check the arithmetic.
What formula does the Boiler Efficiency Calculator use?
Efficiency = useful heat output ÷ fuel energy input × 100 (direct method). The visible formula section above lists the calculation path and the edge cases the page handles, so the result can be checked without relying on the form alone.
Can the Boiler Efficiency Calculator be used for exact decisions?
Use it as a calculation aid, not as a substitute for checking the underlying rule, contract, policy, or professional advice that applies to your situation. When a result depends on local rules, personal details, prices, or dates, enter those values yourself and confirm them before acting.
Sources
Method based on U.S. Department of Energy.
Cite this page
Free Calculator. (2026, October 20). Boiler Efficiency Calculator. https://freecalculator.tech/tools/boiler-efficiency-calculator
"Boiler Efficiency Calculator." Free Calculator, 20 Oct. 2026, https://freecalculator.tech/tools/boiler-efficiency-calculator.
Boiler Efficiency Calculator — Free Calculator, https://freecalculator.tech/tools/boiler-efficiency-calculator
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