Convert power plant heat rate to thermal efficiency, or calculate heat rate in Btu/kWh or kJ/kWh from efficiency or fuel input and electricity output.

Fuel heat input per kWh generated. Compare HHV with HHV and net with net output.

Optional settings
Blank omits fuel cost. Use the same HHV or LHV basis as the heat input.

Heat Rate and Efficiency Formula

The following equations relate heat rate and (thermal) efficiency.

HR = TEI / EEO eta(%) = (EEO / TEI) × 100
  • Where HR is the heat rate (for example, kJ/kWh or Btu/kWh)
  • Where η is the thermal efficiency (%)
  • TEI is the thermal energy input
  • EEO is the electrical energy output

To calculate heat rate, divide thermal input energy by electrical output (kJ/kWh or BtuIT/kWh). For efficiency, first convert both energies to the same unit, then divide electrical output by thermal input and multiply by100. Use a consistent HHV/LHV fuel basis and gross/net output boundary;1 kWh =3,600 kJ =3,412.141633 BtuIT.

Steam-cycle heat rate from flow and enthalpy

Select Steam-cycle heat rate and enter main steam flow, main-steam and feedwater enthalpy, and electrical output from the same steady operating period. Choose whether to include one reheat stage; when included, enter its measured flow and hot/cold enthalpies. Use enthalpies from a consistent steam-table reference.

H = mms(hms − hfw) + mrh(hhot − hcold), with H in kJ/h, flows in kg/h and enthalpies in kJ/kg. Omit the reheat term when absent. HR = H / P in kJ/kWh for electrical output P in kW; η = 3,600 / HR × 100%. Divide HR by 1.05505585262 to obtain Btu/kWh.

For example, 100,000 kg/h of steam heated from 500 to 3,000 kJ/kg adds 250,000,000 kJ/h. At 25,000 kW electrical output, HR = 10,000 kJ/kWh (9,478.1712 Btu/kWh) and cycle electrical efficiency = 36%. Adding 80,000 kg/h of reheat from 2,800 to 3,300 kJ/kg raises the heat input to 290,000,000 kJ/h; at 30,000 kW, HR = 9,666.6667 kJ/kWh and efficiency = 37.2414%.

This is a steam-side energy balance, excluding boiler fuel losses; it is not turbine isentropic efficiency. In backpressure or extraction cogeneration systems, this electrical-only result assigns no credit to useful process heat. It therefore does not represent total CHP efficiency or fuel heat rate allocated between heat and power. Additional heat streams, spray flows, leakage and other boundary corrections require a fuller plant balance. The Bureau of Energy Efficiency turbine assessment guide describes the basic steam-flow/enthalpy heat-rate relation and the need for plant-specific measurements.

To compare the steam energy delivered by a boiler with its fuel energy input, use the Boiler Efficiency Calculator. It provides direct steam-and-fuel and heat-loss methods; boiler efficiency and steam-cycle electrical efficiency use different energy boundaries.

What is Heat Rate (Efficiency)?

Definition:

Heat rate is a measure of how much thermal (fuel) energy a power plant must supply to produce one unit of electrical energy, commonly expressed as Btu/kWh (or kJ/kWh). A lower heat rate means the plant converts fuel to electricity more efficiently (higher thermal efficiency).

Heat rate is useful for comparing generating units, estimating fuel use, and estimating fuel cost and emissions (when combined with fuel heating value and emission factors). However, overall cost-effectiveness depends on many factors besides heat rate, including fuel price, capital cost, operating and maintenance costs, and capacity factor.

Heat rate and efficiency are inversely related. For example:

  • Efficiency (%) ≈ (3412.142 / Heat Rate in Btu/kWh) × 100
  • Efficiency (%) ≈ (3600 / Heat Rate in kJ/kWh) × 100

Heat rates depend on technology, load, fuel-energy convention and gross/net output. Compare only consistent boundaries and heating-value bases. The calculator provides an illustrative ±5% heat-rate sensitivity rather than a technology rating. Its non-electric share includes all other energy uses/losses and is not solely condenser heat; optional fuel-only cost excludes capital, operating and other generation costs.