How to Calculate Scope 1 Stationary Combustion Emissions
Stationary combustion—boilers, furnaces, turbines, emergency generators—typically anchors Scope 1 greenhouse-gas inventories. Converting fuel consumption into auditable CO₂e requires more than multiplying volumes by a static factor. You must align energy content with the correct emission factors, incorporate oxidation adjustments, treat biogenic portions separately, and report CH₄ and N₂O using the global warming potentials mandated by your programme. This guide provides a structured methodology for sustainability teams, internal auditors, and consultants who need defensible, repeatable results.
The workflow mirrors best practice from the Greenhouse Gas Protocol, the U.S. EPA, and ISO management systems. It complements market-based electricity calculations in the Scope 2 guide and upstream accounting discussed in the Scope 3 purchased goods walkthrough, ensuring your entire inventory shares consistent assumptions.
Definition and boundary
Scope 1 stationary combustion covers direct emissions from burning fuels in fixed equipment within your organisational boundary. Include on-site boilers, thermal oil heaters, combined heat-and-power units, furnaces, and stationary backup generators. Exclude mobile combustion (vehicles) and process emissions (for example, calcination) unless specifically scoped. Report fossil CO₂ separately from biogenic CO₂ when fuels contain biomass blends.
Boundaries should align with financial consolidation rules. If you operate leased facilities, determine whether operational control gives you responsibility for the equipment. Document meter IDs, fuel contracts, and any allocation keys used to apportion shared systems among tenants or business units.
Variables, symbols, and units
Convert physical fuel quantities (gallons, therms, tonnes) into energy using lower heating value. Maintain consistent units—MMBtu or GJ—for energy and kilograms for emissions.
- E – Fuel energy consumed (MMBtu) over the reporting period.
- EFCO₂ – CO₂ emission factor (kg CO₂ per MMBtu).
- EFCH₄, EFN₂O – Optional methane and nitrous oxide factors (kg gas per MMBtu).
- OX – Oxidation completeness factor (%), representing the share of carbon that oxidises to CO₂.
- Bio – Biogenic fraction of the CO₂ factor (%).
- GWPCH₄, GWPN₂O – Global warming potentials applied to methane and nitrous oxide.
- Emissions – Resulting kg and tonnes CO₂e.
Keep a factor library that records sources (EPA AP-42, IPCC tables, national inventory). Version-control the file so auditors can see when factors change and why. For blended fuels, capture blend ratios and heating values for each component.
Equations
Fossil CO₂ = E × EFCO₂ × (OX ÷ 100) × (1 − Bio ÷ 100)
CH₄ CO₂e = E × EFCH₄ × GWPCH₄
N₂O CO₂e = E × EFN₂O × GWPN₂O
Total Scope 1 stationary combustion CO₂e = Fossil CO₂ + CH₄ CO₂e + N₂O CO₂e
Report totals in kilograms and tonnes. If your reporting framework requires separate biogenic disclosure, calculate biogenic CO₂ as E × EFCO₂ × (OX ÷ 100) × (Bio ÷ 100) and present it alongside fossil emissions without aggregating into Scope 1.
When factors are provided in different units (for example, kg per GJ), convert energy to match before applying the formula. Avoid mixing higher heating value (HHV) and lower heating value (LHV) data—stay consistent with the factor source.
Step-by-step workflow
Step 1: Gather activity data
Collect metered fuel consumption for each stationary source. Reconcile deliveries, invoices, and storage tank changes to ensure completeness. For natural gas, cross-check utility bills against building management system data. Document any estimations applied when meters fail.
Step 2: Convert to energy
Convert physical units to energy using the appropriate heating value. Many organisations maintain a conversion sheet; others use calculators such as the greenhouse gas unit converter to stay consistent with regulatory reporting.
Step 3: Apply emission factors and adjustments
Select CO₂, CH₄, and N₂O factors for the fuel and combustion technology. Apply oxidation factors published by the EPA or regional authorities when combustion is incomplete; otherwise default to 100%. For biomass blends, determine the biogenic share from supplier documentation or lab assays. Record the global warming potentials specified by your reporting programme (AR5, AR6, or regulatory equivalents).
Step 4: Calculate emissions and review
Run the calculations manually or via the embedded tool. Summarise results per site and asset, and reconcile totals with previous years. Investigate variances exceeding ±10% that cannot be explained by production changes or weather-normalised heating degree days.
Step 5: Document and integrate
Archive factor sources, meter readings, calculation workbooks, and approval logs in a controlled repository. Link Scope 1 outcomes with Scope 2 market-based analyses and Scope 3 supply chain data to build a coherent emissions narrative across the inventory.
Validation and QA
Validate the energy conversion by comparing calculated consumption against utility invoices and facility production metrics. Sample invoices quarterly to ensure rate changes or measurement corrections do not slip into the wrong period. Use regression analysis (fuel use versus heating degree days) to flag anomalies.
When internal audit or third-party assurance is anticipated, pre-build an audit package containing factor references, unit conversions, and reconciliation tables. Align QA cadence with the reporting cycle—monthly or quarterly reviews catch issues earlier than annual scrubs.
Limits and interpretation
Emission factors are averages. Facility-specific combustion conditions, maintenance regimes, and fuel quality can introduce variability that the standard factors do not capture. When material, commission stack tests or continuous emissions monitoring (CEMS) to replace default factors.
Biogenic accounting differs across frameworks: some jurisdictions require reporting biogenic CO₂ outside Scope 1 totals, while others fold it into separate memo lines. Track policy developments and ensure disclosures remain compliant. When fuel switching projects shift energy balances, update baseline assumptions so efficiency programmes and carbon abatement plans remain accurate.
Embed: Scope 1 stationary combustion calculator
Use the embedded calculator to input fuel energy, emission factors, oxidation assumptions, and global warming potentials. The tool outputs kg and tonnes CO₂e with a breakdown by gas, mirroring the documentation you need for assurance files and ESG disclosures.