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Heat conduction through a slab
Estimate steady heat conduction through one flat homogeneous layer.
Calculators / Science / Heat engine efficiency
Heat engine efficiency calculator
Calculate thermal efficiency and rejected heat from heat input and work output.
On this page
Efficiency30%
Rejected heat700J
Calculator controls
How to calculate
Calculate thermal efficiency and rejected heat from heat input and work output.
Efficiency = w/q*100 %; Rejected heat = q-w J
Worked example
Heat input (J): 1000; Useful work output (J): 300.
Efficiency: 30 %; Rejected heat: 700 J.
Assumptions and limits
Assumes a complete engine cycle with no net change in stored energy. Work output must not exceed heat input; this does not include a heat pump’s coefficient of performance.
Results are rounded for display; calculations use unrounded values. Read our calculation methodology.
Understanding the result
Calculate thermal efficiency and rejected heat from heat input and work output.
When this tool is useful
Efficiency = w/q*100 %; Rejected heat = q-w J
Understanding your inputs
| Input | What to enter |
|---|---|
| Heat input (J) | Enter a number of at least 1e-12 and no more than 1000000000000. |
| Useful work output (J) | Enter a number of at least 0 and no more than 1000000000000. |
Frequently asked questions
What assumptions does this calculation use?
Assumes a complete engine cycle with no net change in stored energy. Work output must not exceed heat input; this does not include a heat pump’s coefficient of performance.
How is the result calculated?
Efficiency = w/q*100 %; Rejected heat = q-w J