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

Canonical: https://senseible.earth/answers/waste-oil-burner-furnace-co2-factor

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](https://senseible.earth/calculators)
- [Used engine oil in a vehicle workshop](https://senseible.earth/answers/workshop-used-engine-oil-emissions-scope)
- [Furnace oil litres to kilograms](https://senseible.earth/answers/furnace-oil-litres-to-kg-density)
- [GCV or NCV in fuel calculations](https://senseible.earth/answers/gcv-vs-ncv-in-fuel-emission-calculation)

Sources: [IPCC 2006 Guidelines, Volume 2, Chapter 2 Stationary Combustion, Tables 2.3 to 2.7](https://www.ipcc-nggip.iges.or.jp/public/2006gl/pdf/2_Volume2/V2_2_Ch2_Stationary_Combustion.pdf), [IPCC 2006 Guidelines, Volume 2 Energy, Table 1.2 (net calorific values) and Chapter 2 tables](https://www.ipcc-nggip.iges.or.jp/public/2006gl/vol2.html), [IPCC AR6 Working Group I, Chapter 7, global warming potentials (methane 27.0 non fossil, 29.8 fossil; nitrous oxide 273)](https://www.ipcc.ch/report/ar6/wg1/)

Last reviewed 2026-10-31.