Steam reaches our processes from two boilers. What does the CBAM verifier need to split it?
Proof that a given boiler's steam reaches a given process. Without it, the Commission's template works as for electricity: one weighted average heat factor across the installation. With it, each process takes its own boiler's factor. The verifier accepts separate heat balances for separate steam networks, or flow charts showing a boiler feeds only certain users.
Why the split moves your figure
Your coal-fired boiler and your gas-fired boiler, or your waste heat recovery boiler, produce steam with very different emissions per gigajoule. If the CBAM good's process draws only from the cleaner source, averaging hands it part of the coal boiler's emissions. The calculation of attributed emissions for each production process gives every heat flow into and out of the process its own emission factor, so the question is which factor, and the verifier decides that from your evidence.
What the rules say, and do not say
- The Methodology Act has no dedicated heat rule like the ones for precursors and electricity.
- The Commission's emissions report template has a tool for heat from several sources that works like the electricity one: an installation-wide average by default, process-specific where you can show the link.
- Cooling counts in the same way as heat.
- Only the reporting period being verified matters.
Evidence the guidance names
A shared header where both boilers' steam mixes offers neither kind of proof, which usually leaves the users on it with the average.
- Separate steam networks, for example a high pressure header and a low pressure header, each with its own heat balance.
- Flow charts of the installation showing heat goes from one or a few sources to one or a few users only.
Put this together before the verifier arrives
- A drawing of each steam network: which boiler feeds it, which users draw from it, and every crossover valve.
- A heat balance per network for the year: heat produced by each boiler against heat used by each process, from steam flow meters where you have them.
- Fuel records for each boiler, matching the fuel totals in your emissions report.
- A note on any crossover valve: when it was open, and how you counted that steam.
- The same split written into your monitoring plan, so the method on paper matches the plant.
What the verifier will look at
Heat flows between processes are one of the completeness checks a CBAM team is expected to make, and heat moving into, out of or across the installation is something the verifier plans for in its strategic analysis. Where it is complex, it may bring a technical expert. The site visit is where it checks technical connections against your drawings, so expect it to walk the headers.
Worked example: a coal boiler and a gas boiler, example figures
- Coal boiler: 30,000 GJ of steam at 0.12 t CO2 per GJ = 3,600 t CO2
- Gas boiler: 10,000 GJ of steam at 0.07 t CO2 per GJ = 700 t CO2
- Installation average: (3,600 + 700) / 40,000 = 0.1075 t CO2 per GJ
- The CBAM good's process uses 8,000 GJ, all on the low pressure network fed only by the gas boiler
- Averaged: 8,000 x 0.1075 = 860 t CO2. Split with evidence: 8,000 x 0.07 = 560 t CO2
- Difference: 300 t CO2. Over 5,000 t of product, that is 0.172 against 0.112 t CO2 per tonne from heat
The heat factors and quantities are example figures, not Commission values. Your own factors come from each boiler's fuel and output under the Methodology Act.
What Senseible does here
Senseible reads your coal, gas and oil invoices into dated records with quantities, so the fuel totals behind each heat balance trace back to a bill. We build it from your records, check every figure in-house, and an accredited verifier we partner with signs it off. Have your own verifier? Send it to them.
- Prepare your CBAM file
- Steam bought from a neighbouring plant
- Splitting CHP emissions between power and steam
- What the verifier checks on site
Last reviewed 2026-11-03.