Heat rate is a measurement of how efficient a power station generator is in its use of heat energy. It is calculated as the number of BTUs of heat required to generate one KWH of electricity. Every type of fuel (coal, natural gas, fuel oil, diesel) has its own heat rate so that it is possible to calculate relatively accurately the amount of heat energy a certain amount of any type of fuel, so when this is compared to the actual energy produced by the generator, the resulting figure tells how efficiently the generator converts that fuel into electrical energy.

In a power plant, the conversion rate of MMBTU to MWH hours determines the plant’s efficiency and is known as the plant’s heat rate. 1 MWH is equivalent to 3.412 MMBTU. Thus if a generator could convert all of the energy from the fuel into electric energy, its heat rate would be 3.412 MMBTU/MWH. Generators cannot come anywhere close to 100% efficiency. The better units being around 50% efficiency. This translates into a heat rate of 6.824 MMBTU/MWH, meaning that producing one MWH of electric energy requires burning fuel with a heat content of 6.824 MMBTU. 1 MWH is thus equal to 3,412,142 btu. 1 KWH is equal to 0.003412 MMBTU or 3,412 BTU