Carnot Efficiency Calculator
The ceiling no engine gets past, and the heat-pump COP.
Work out Carnot Efficiency. The ceiling no engine gets past, and the heat-pump COP. Says where the approximation stops holding.
Absolute temperature. Add 273.15 to a Celsius figure.
Maximum possible efficiency
40.00%
60.0% must be rejected as waste heat
This is a ceiling set by thermodynamics, not by engineering. No amount of design gets past it, and real engines fall well short — a car engine sits around 25–35% against a Carnot limit near 85%. The only routes to a higher ceiling are a hotter source or a colder sink, which is why power stations invest so heavily in condenser temperature and why combined-cycle plants stack a second engine on the first one's waste heat. Run backwards it becomes a heat pump, and the coefficient of performance exceeds 1 — which is not a violation of anything, because the device moves heat rather than creating it. That is why a heat pump beats a resistive heater by a factor of three or four.
How the Carnot Efficiency Calculator works
Enter the hot and cold reservoir temperatures in kelvin for the maximum efficiency any heat engine can reach between them, and the coefficient of performance if you run it backwards as a heat pump.
Also known as: heat engine efficiency calculator · carnot cycle calculator · maximum thermal efficiency calculator · coefficient of performance calculator
Frequently asked questions
What is Carnot efficiency?
η = 1 − Tc/Th, with both temperatures absolute. It is the theoretical maximum for any heat engine operating between those two reservoirs.
Why can no engine beat it?
Because it follows from the second law of thermodynamics, not from engineering limits. Better materials and tighter tolerances close the gap to the ceiling but never raise it.
How efficient are real engines?
A petrol engine manages 25–35% against a Carnot limit near 85%. Combined-cycle power stations reach about 60% by stacking a second engine on the first one's waste heat.
How can a heat pump be more than 100% efficient?
It is not creating energy, it is moving it. The coefficient of performance can be 3 or 4 because the device transports heat from outside rather than generating it, which is why heat pumps beat resistive heaters so comfortably.
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