Do the Intergovernmental Panel on Climate Change default fuel factors assume every bit of the carbon burns, even in an ash-heavy coal boiler?

Yes. The Intergovernmental Panel on Climate Change (IPCC) builds each carbon dioxide (CO2) default as carbon content times an oxidation factor of 1 times 44/12, so unburnt carbon is ignored. IPCC says the unoxidised fraction is usually small, with 99 to 100 percent of carbon oxidised, and that measured values should be used where available.

How a default is built

• Table 1.4 prints the formula: effective CO2 emission factor in kilograms (kg) per terajoule (TJ) = A x B x 44/12 x 1,000, where A is the carbon content in kg per gigajoule (GJ) from Table 1.3 and B is the oxidation factor.
• B is 1 for every fuel in the table. IPCC says the unoxidised fraction is usually small, with 99 to 100 percent of the carbon oxidised, and that for some fuels it may not be negligible. The defaults are derived on the assumption of 100 percent oxidation.
• Defaults are rounded to three significant digits, which is why the products below are close to, not equal to, the printed values.

Checking the table yourself

• Gas or diesel oil: 20.2 x 44/12 x 1,000 = 74,067, printed as 74,100.
• Natural gas: 15.3 x 44/12 x 1,000 = 56,100, printed as 56,100.
• Liquefied petroleum gases: 17.2 gives 63,067, printed as 63,100.
• Petroleum coke: 26.6 gives 97,533, printed as 97,500.
• Other bituminous coal: 25.8 gives 94,600, printed as 94,600.
• Wood and wood waste: 30.5 gives 111,833, printed as 112,000.

What IPCC says to do when burning is not complete

• For some fuels the unoxidised fraction may in practice not be negligible, and where representative country-specific values, based on measurements are available, they should be used.
• My reading for a plant: if your ash carries measurable unburnt carbon, the default slightly overstates CO2 from a coal or biomass boiler. The remedy is a measured fraction, not a guess.
• My reading: without a measurement, keep B = 1 and say so. That choice errs high. Ask your buyer or verifier whether they accept it.
• The answer on this site about the Central Electricity Authority (CEA) shows its grid database applying 0.98 for Indian coal. That is a national grid calculation, not a rule for your boiler.

1,000 tonnes of coal with a measured unburnt share, example

• Default: 1,000 t x 25.8 GJ per tonne = 25,800 GJ; x 94.6 kg per GJ = 2,440,680 kg, 2,440.7 t CO2
• Suppose an ash test shows 1.5% of the fuel's carbon leaves unburnt (example): B = 0.985
• Adjusted: 2,440.7 x 0.985 = 2,404.1 t CO2. The default overstated by 36.6 t, 1.5%
• The adjustment is only as good as the ash sampling behind the 1.5%. Keep the lab report and the sampling dates

The 1.5% is an example, not a typical figure for any boiler. 25.8 GJ per tonne is IPCC's default net heat value for other bituminous coal.

What Senseible does here

Senseible reads fuel invoices and electricity bills into monthly records. An unburnt carbon figure from an ash test is your own measurement, so keep the report beside the records and say which factor you used.

• Using coal carbon content from a lab
• CEA coal and lignite factors
• Will a buyer accept IPCC Tier 1 factors?
• Is my lab CO2 factor within the IPCC range?

Sources: IPCC 2006 Guidelines, Volume 2, Chapter 1 (Tables 1.2, 1.3 and 1.4 and the text on carbon oxidation)

Last reviewed 2026-11-05. Ask your buyer or verifier whether they accept an oxidation factor below 1 for a plant, and what ash evidence they expect.