Combustion Emissions
Combustion emissions are greenhouse gases released when fossil fuels or biofuels are burned for energy. They include CO₂, CH₄, and N₂O produced from the burning of natural gas, diesel, petrol, LPG, fuel oil, and other fuels in boilers, furnaces, engines, and generators.
What is Combustion Emissions?
Combustion emissions are the most common and widely understood form of greenhouse gas emissions. They result from the chemical reaction between a carbon-based fuel and oxygen, producing carbon dioxide (CO₂) as the primary product, along with smaller quantities of methane (CH₄) and nitrous oxide (N₂O). Under the GHG Protocol, combustion emissions from sources owned or controlled by the organisation are classified as Scope 1 direct emissions.
Combustion sources are divided into stationary and mobile. Stationary combustion includes natural gas boilers for space heating and hot water, diesel or gas oil generators for backup power, industrial furnaces and kilns, and biomass boilers. Mobile combustion includes company-owned cars, vans, trucks, and heavy plant running on petrol, diesel, LPG, or CNG. Each fuel type has a specific DEFRA emission factor that converts the quantity consumed (in kWh, litres, or tonnes) into kgCO₂e.
The emission factor for each fuel reflects its carbon content and combustion characteristics. Natural gas produces approximately 0.183 kgCO₂e per kWh. Diesel produces approximately 2.51 kgCO₂e per litre. Petrol produces approximately 2.17 kgCO₂e per litre. Gas oil (red diesel) produces approximately 2.76 kgCO₂e per litre. These factors include the CO₂, CH₄, and N₂O components combined into a single CO₂e figure.
For biofuels and biomass, the treatment is different. The CO₂ released from burning biologically derived fuels is classified as biogenic and reported separately from fossil fuel CO₂ under the GHG Protocol. However, the CH₄ and N₂O components of biofuel combustion are included in the Scope 1 total because these gases have warming effects regardless of the fuel's biological origin.
Reducing combustion emissions is one of the most direct decarbonisation levers available. Strategies include electrifying heating systems (replacing gas boilers with heat pumps), transitioning vehicle fleets to electric or hydrogen, switching to lower-carbon fuels (e.g., hydrotreated vegetable oil — HVO — as a diesel substitute), and improving combustion efficiency through equipment upgrades and building insulation.
Practical Examples
A manufacturing facility burns 2,000,000 kWh of natural gas annually in its process heaters — the combustion produces approximately 366 tCO₂e, calculated using the DEFRA natural gas factor.
A construction company consumes 80,000 litres of red diesel across its fleet of excavators, cranes, and generators on site, producing approximately 220.8 tCO₂e of Scope 1 combustion emissions.
An office building's gas boiler consumes 400,000 kWh of natural gas for heating, producing approximately 73.2 tCO₂e — the single largest Scope 1 source for the business.
How Climatise Helps
Climatise automatically identifies fuel types from your uploaded bills and invoices, matches each to the correct DEFRA combustion emission factor, and calculates Scope 1 combustion emissions. The platform separates biogenic CO₂ from fossil fuel CO₂ where relevant and tracks fuel consumption trends to highlight reduction opportunities.
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