What emission factor applies when a furnace burns used or waste oil?

About 3.03 t CO2e per tonne of waste oil burned in a factory furnace, from IPCC 2006 defaults: 73,300 kg CO2 per TJ at 40.2 GJ a tonne, plus small methane and nitrous oxide. It is fossil Scope 1, and only about 5% lower than furnace oil per unit of heat.

The IPCC defaults for waste oil

• CO2: 73,300 kg per TJ, with a 95% range of 72,200 to 74,400 (IPCC 2006, Table 2.3, manufacturing industries).
• Methane: 30 kg per TJ (range 10 to 100). Nitrous oxide: 4 kg per TJ (range 1.5 to 15).
• Heat content: 40.2 GJ per tonne net (Table 1.2), but the range runs from 20.3 to 80.0, the widest of any oil.
• IPCC defines waste oils as used oils, such as spent lubricants, burned for heat. None of it is biogenic, so all of it goes in Scope 1.

Why the heat content matters more than the factor

The CO2 factor per TJ is tight. The heat per tonne is not: used oil can carry water and sludge, so two tankers can differ a lot. The default 40.2 GJ gives 2.95 t CO2 per tonne. If a lab test on your oil shows 36 GJ, the same tonne gives 2.64 t.

Ask your supplier for a net calorific value on each lot, or send a sample for testing twice a year. Keep the certificate with the invoice.

Compared with furnace oil

Furnace oil is 77,400 kg CO2 per TJ at 40.4 GJ a tonne, about 3.13 t CO2 per tonne. Per unit of heat, waste oil comes out about 5% lower. Switching saves money, not much carbon, and a buyer reading your report should see it as fossil fuel, not a recycled or low carbon one.

What to record each month

• Quantity received in kg or litres, from the invoice, and the density if it is billed in litres.
• Stock at the start and end of the month, so you report oil burned, not oil bought.
• The lot's calorific value certificate, if you have one.
• If the oil fires a space heater in an office or canteen, IPCC's commercial table uses 300 kg methane per TJ, ten times the factory figure.

A forging furnace burning 60 t of waste oil a year (estimate)

• Heat: 60 t x 40.2 GJ = 2,412 GJ
• CO2: 2,412 GJ x 73.3 kg = 176.8 t
• Methane: 2,412 GJ x 0.030 kg = 72 kg x 29.8 = 2.2 t CO2e
• Nitrous oxide: 2,412 GJ x 0.004 kg = 9.6 kg x 273 = 2.6 t CO2e
• Total: about 181.6 t CO2e, or 3.03 t per tonne of oil

IPCC 2006 defaults with AR6 warming potentials (fossil methane 29.8, nitrous oxide 273). Replace 40.2 GJ with your lab figure where you have one.

What Senseible does here

Senseible reads fuel invoices into monthly records, but it has no built-in factor for waste oil, so a waste oil line waits for a factor rather than being guessed. Use the figure worked out here, and see how your total compares on the calculators page.

• Carbon calculators
• Used engine oil in a vehicle workshop
• Furnace oil litres to kilograms
• GCV or NCV in fuel calculations

Sources: IPCC 2006 Guidelines, Volume 2, Chapter 2 Stationary Combustion, Tables 2.3 to 2.7, IPCC 2006 Guidelines, Volume 2 Energy, Table 1.2 (net calorific values) and Chapter 2 tables, IPCC AR6 Working Group I, Chapter 7, global warming potentials (methane 27.0 non fossil, 29.8 fossil; nitrous oxide 273)

Last reviewed 2026-10-31.