Purchased Steam and Heat Emissions
You buy heat by the kilowatt-hour delivered to your boundary. The supplier burns the fuel, runs the boiler, and absorbs the conversion losses long before the steam reaches your pipe. Account for the heat as if you burned the fuel yourself and the number is wrong; account for it as zero because “we didn’t combust anything” and it’s wrong the other way.
Purchased steam and heat is Scope 2 — and like purchased electricity, it carries two numbers, not one.
Purchased steam, hot water, and district heat are Scope 2 emissions. Multiply delivered heat (kWh) by a heat emission factor — supplier-specific, efficiency-derived, or a default network factor — and report both a location-based and a market-based figure.
Purchased thermal energy — steam, hot water, and district heat consumed from a third-party network or a supplier-owned on-site plant — is one of the most under-documented corners of Scope 2 accounting. The arithmetic is simple: delivered heat times an emission factor. The judgement is everything else — whether to use a supplier-specific factor, derive one from the input fuel and plant efficiency, or fall back to a network default; how to handle combined heat and power; and how delivery losses and upstream fuel land in the inventory. This page covers all of it, with three worked examples and the GHG Protocol Scope 2 Guidance dual-reporting model applied to heat rather than electricity.
What Counts as Purchased Steam and Heat
This methodology covers thermal energy your organisation imports and consumes but does not generate — the heat equivalent of buying electricity from the grid. It is a Scope 2 method.
1.1 Purchased steam and district heat
Process steam piped from a neighbouring plant, district-heating networks serving campuses and cities, and heat supplied under an energy-services contract where a third party owns and operates the boiler or CHP plant. The defining feature is that combustion happens outside your operational boundary — you meter and consume the delivered heat.
1.2 Hot water
Hot water delivered from a district network or a shared central plant, metered in kWh of thermal energy at the point of delivery. Accounted identically to steam — the medium differs, the method does not.
1.3 What is not covered here
- Heat from a boiler you own and operate — that is Scope 1 stationary combustion, accounted on the fuel you burn via the natural gas or other fuel-combustion methodology. The fuel is yours; the emissions are direct.
- Purchased electricity — Scope 2 as well, but accounted via a grid or supplier factor under the Scope 2 electricity methodology.
- District cooling — chilled water from a central plant is its own calculation (electric chiller efficiency, kW per ton); see the district heating and cooling methodology.
- Upstream fuel extraction and processing — the well-to-tank portion of the supplier’s fuel is Scope 3 Category 3, reported separately. See §9.
Provider directory
Now it has to hold up all year.
See who does this work. Every listing names the standards it works to, and paid placements are labelled. Including The Carbon Trust and Attain Zero.
Browse 6 carbon accounting & inventory providers →Do this work? A listing is US$390 a year. Get listed →
Why Purchased Heat Is Scope 2
The scope assignment turns on a single test: who owns and operates the combustion equipment. If you burn the fuel, the emissions are Scope 1. If a third party burns the fuel and delivers you the resulting energy, the emissions are Scope 2 — indirect emissions from purchased energy. Purchased steam, hot water, and district heat sit alongside purchased electricity in Scope 2 for exactly this reason.
The ownership-and-operation test settles the scope: combust the fuel yourself and it is Scope 1; consume third-party-generated heat and it is Scope 2. A common error is to push purchased steam into Scope 1 because “it’s combustion” — but it is not your combustion, and accounting it as Scope 1 double-counts against the supplier’s own inventory.
Dual Reporting: Location-Based and Market-Based
The GHG Protocol Scope 2 Guidance requires two parallel figures for purchased energy, and the requirement applies to heat as much as to electricity. Both are reported; neither replaces the other.
Network or default factor
Reflects the average emissions intensity of the heat network or grid the consumer is physically connected to. Uses the default network factor (e.g. the DEFRA district-heat factor) or a regional average. This figure is reported regardless of any contract. See location-based.
Supplier-specific or contractual factor
Reflects the emissions intensity the consumer has contracted for — a supplier-specific heat factor, a green-heat tariff, or a contractual instrument. Falls back to the network factor where no contractual claim exists. See market-based and the location-vs-market comparison.
For heat specifically, the market-based figure most often diverges from the location-based one where the consumer has a supplier-specific factor from the operator of the network — a verified figure for the actual plant, which can be markedly different from the network or national average. Where no such instrument or supplier factor exists, the two figures converge on the network default.
Three Ways to Derive the Heat Emission Factor
The heat emission factor — kg CO₂e per kWh of delivered thermal energy — can be derived three ways. They form a data-quality hierarchy: use the highest tier your data supports, and document the route you took.
fuels.gbr.<fuel>.kwh_gcv; efficiency from the plant operator. The delivered factor is always higher than the raw fuel factor because of conversion loss.
district_heating.gbr.district (UK) or the EU fossil-DH baseline district_heating.eu_framework.fossil_dh_baseline_ef.
The screening tier. Drives the location-based figure; serves as the market-based fallback where no contractual claim exists.
The district-heat factors are dotted-key MasterBrain rows and must be read with the universal [gc_factor key="district_heating.gbr.district"] resolver. The convenience [gc_fuel] handler is for the flat fossil-fuel keyspace and renders an em-dash for these dotted keys. Always preview the live page and confirm every heat factor resolved to a number.
The CHP Allocation Problem
Combined heat and power (cogeneration) plants produce two useful outputs from one fuel input. If you take the entire fuel emission and assign it to the heat stream, you overstate the heat factor and double-count against whoever consumes the electricity. The fuel emissions must be allocated between the heat and power outputs before the heat factor is derived.
5.1 The energy / efficiency allocation method
The most common approach allocates the plant’s total combustion emissions to each output in proportion to the energy delivered, adjusted for the reference efficiency of producing each output separately. The heat stream receives its allocated share; that share, divided by the heat delivered, is the heat emission factor.
The allocation fraction is the supplier’s responsibility to derive and disclose, and the consumer’s responsibility to confirm. The full allocation mechanics — energy method, exergy method, and the reference-efficiency approach — are covered in the CHP cogeneration allocation methodology. For purchased-heat accounting, the practical rule is: never use a CHP plant’s unallocated fuel factor as the heat factor.
Assigning 100% of a CHP plant’s fuel emissions to the heat stream can overstate the heat factor by a factor of two or more, depending on the heat-to-power ratio. The emissions belong to two outputs; allocate before you derive. If the supplier cannot provide an allocation, treat the figure as low quality and prefer a network default for the location-based line.
Governing Standards
Four layers govern purchased-heat accounting. They nest: each supplies a different input to the same Scope 2 output.
method
Defines the dual-reporting requirement (location-based + market-based), the quality hierarchy for emission factors, the contractual-instrument criteria for market-based claims, and the treatment of purchased steam, heat, and cooling as Scope 2.
boundary
Sets the organisational and operational boundary that determines whether combustion is yours (Scope 1) or a supplier’s (Scope 2), and the consolidation approach applied across the inventory.
set
DEFRA publishes combined district-heat and on-site-heat factors (kg CO₂e/kWh) with well-to-tank companions — the default-tier network factors. EUROSTAT supplies per-country renewable-share data for adjusting a fossil baseline toward a network’s actual mix. DEFRA heat factors carry an AR5 GWP basis by convention; see §7.
science
Supplies the global warming potentials that convert the non-CO₂ combustion gases inside a heat factor to CO₂e — fossil CH₄ 29.8, N₂O 273 — for any factor you derive from first principles.
Calculating Purchased-Heat Emissions
7.1 The general formula
At its simplest, purchased-heat emissions are delivered heat times a delivered-heat emission factor. The factor already incorporates the supplier’s conversion losses and fuel mix — that is what makes it a delivered-heat factor.
7.2 The efficiency-method derivation
When you derive the factor yourself from a known input fuel and plant efficiency, divide the fuel’s emission factor by the conversion efficiency. The delivered-heat factor is always larger than the raw fuel factor — because some of the fuel’s energy is lost as the heat is generated and delivered.
2.02633
7.3 GWP basis discipline
Corporate reporting under the GHG Protocol, CSRD, SBTi, and CDP uses AR6 GWP-100 by default. DEFRA-sourced factors — including the district-heat rows used here — carry an AR5 GWP basis internally by DEFRA convention. This asymmetry is by design: the DEFRA factors are pre-baked at AR5 and that basis is part of their definition. Do not convert them, and do not sum an AR5-basis DEFRA heat line with an AR6-basis line inside the same total. Where a strict AR6 inventory is required, derive the factor from first principles using AR6 GWPs, or document the AR5 retention for the DEFRA line.
Emission Factors
The tables render live from the MasterBrain — each value self-heals when DEFRA or EUROSTAT publishes a new vintage. Use the default-tier factors below only where supplier-specific or efficiency-derived factors are unavailable.
8.1 DEFRA district-heat and on-site-heat factors (UK)
| Factor | Combustion Scope 2 | Well-to-tank Scope 3 Cat 3 |
|---|---|---|
| District heat & steam (networked) | 0.17529 kg CO₂e/kWhdistrict_heating.gbr.district | 0.03341 kg CO₂e/kWhdistrict_heating.gbr.district_wtt |
| On-site heat & steam (supplier plant on your site) | 0.17529 kg CO₂e/kWhdistrict_heating.gbr.onsite | 0.03341 kg CO₂e/kWhdistrict_heating.gbr.onsite_wtt |
DEFRA 2026 district heating factors · AR5 GWP basis (DEFRA convention) · combustion column is the Scope 2 delivered-heat factor, well-to-tank column is the upstream Scope 3 Category 3 companion. See also the DEFRA factor dataset.
8.2 EU baseline and renewable-share adjustment
Outside the UK, the EU fossil district-heating baseline supplies a default where no national factor or supplier figure is available: 0.215 kg CO₂e/kWh [GreenCalculus district_heating.eu_framework.fossil_dh_baseline_ef · DEFRA 2025 · v2026.203]. This is a fossil-only baseline; where a network carries renewable and waste-heat content, adjust it down using the per-country renewable share. The MasterBrain carries EUROSTAT renewable-share data for around thirty European countries — for example Denmark at 72% [GreenCalculus district_heating.dnk.eurostat.renewable_share · EUROSTAT NRG 2024] and Spain at 82% [GreenCalculus district_heating.esp.eurostat.renewable_share · EUROSTAT NRG 2024] — and the EU-27 aggregate at 34.527% [GreenCalculus district_heating.eu_framework.renewable_share_eu27 · EUROSTAT NRG 2024].
A renewable-share-adjusted baseline is a screening estimate, not a supplier-specific factor. It approximates a network’s intensity by scaling the fossil baseline by the non-renewable fraction. Use it for the location-based figure where no better network factor exists, and replace it with a supplier-specific factor for the market-based figure as soon as one is available.
Delivery Losses and Well-to-Tank
Two further components attach to purchased heat, and they land in different scopes.
9.1 Network delivery losses (Scope 2)
Heat lost in transmission and distribution between the plant and your delivery point is, like electricity T&D loss, an in-scope component. Where you account for it separately rather than relying on a delivered-basis factor, read the DEFRA district-heat T&D factor at transmission_distribution.gbr.district_heat: 0.00945 kg CO₂e/kWh [GreenCalculus transmission_distribution.gbr.district_heat · DEFRA 2026 'Transmission and distribution'!E27], with its well-to-tank companion at transmission_distribution.gbr.district_heat_wtt. A delivered-basis factor already incorporates these losses — do not add them twice.
9.2 Upstream fuel — well-to-tank (Scope 3 Category 3)
The extraction, processing, and transport of the fuel the supplier burns is upstream of combustion and belongs to Scope 3 Category 3, not Scope 2. The DEFRA heat factors carry a paired _wtt companion for exactly this — keep it on the Scope 3 line, never folded into the Scope 2 delivered-heat figure.
Three components, two scopes: the delivered-heat combustion factor and the network delivery loss are both Scope 2; the well-to-tank upstream fuel is Scope 3 Category 3. Folding the WtT companion into the Scope 2 figure overstates Scope 2 and understates Scope 3, and double-counts if the WtT line is also reported correctly elsewhere.
Worked Examples
Three examples, each computed end-to-end. Values are hardcoded — these are audit records at the snapshot date of this revision and must reconcile to their stated inputs a year from now, regardless of any later factor vintage. Illustrative factor values are stated inline; substitute the live MasterBrain value at the time of calculation and re-run.
2,400,000 kWh of district heat over the year, metered at the building heat-exchanger. No supplier-specific factor is available, so the DEFRA district-heat default applies. Illustrative DEFRA 2026 district-heat factor 0.17084 kg CO₂e/kWh; WtT companion 0.02981 kg CO₂e/kWh.
5,000,000 kWh of process steam from a supplier-owned gas boiler on its site. The supplier discloses an 85% thermal efficiency but no emission factor. Derive it: input fuel is natural gas at 0.18231 kg CO₂e/kWh (DEFRA 2026), efficiency η = 0.85.
10,000,000 kg CO₂e in the year, delivering useful heat and electricity. Under the energy/efficiency method the operator allocates 40% of emissions to heat. Your site draws 3,000,000 kWh of the plant’s 20,000,000 kWh total heat output.
Market-Based Instruments for Heat
The market-based figure for heat follows the same instrument hierarchy as electricity, adapted to the thermal market. In descending order of preference:
- Supplier-specific heat factor. A verified kg CO₂e/kWh from the operator of the plant or network serving you — the highest-quality market-based input, reflecting the actual fuel mix, allocation, and any renewable or waste-heat content.
- Contractual instruments and green-heat tariffs. Where a network offers a contractually-backed low-carbon or renewable-heat product, the contracted intensity may be claimed for the market-based figure, provided the instrument meets the Scope 2 Guidance quality criteria (exclusivity, tracking, and no double-claiming).
- Network default fallback. Where no supplier factor or contractual claim exists, the market-based figure falls back to the same network default used for the location-based figure — the two converge.
Because heat networks are physically local and instruments are less mature than for electricity, the supplier-specific factor is by far the most common credible market-based input for heat. Treat green-heat tariff claims with the same scrutiny applied to energy attribute certificates for electricity — the claim is only as good as the tracking behind it.
Reporting Surfaces: CSRD, SECR, SBTi, CDP
Purchased-heat emissions feed the same disclosure regimes as the rest of Scope 2, each with its own expectation.
- CSRD ESRS E1-6. Requires gross Scope 2 disclosed on both a location-based and a market-based basis. Purchased heat and steam are an explicit part of the Scope 2 line; the dual-reporting split must be visible.
- UK SECR. Streamlined Energy and Carbon Reporting follows the DEFRA basis and expects purchased heat and steam consumption (kWh) and the resulting emissions to be reported alongside electricity and own-fuel combustion.
- SBTi. Scope 2 targets are typically set on the market-based figure where a company actively procures low-carbon energy, with the location-based figure disclosed alongside. Purchased-heat decarbonisation counts toward the Scope 2 reduction.
- CDP Climate. The questionnaire asks for Scope 2 location-based and market-based figures separately and scores the quality of the underlying factors. A supplier-specific heat factor scores better than a default.
The line chart below shows an illustrative location-based heat factor falling as a district network adds renewable and waste-heat capacity across several years — the kind of trajectory a market-based supplier-specific factor would track ahead of the network average.
| Point | kg CO₂e/kWh |
|---|---|
| 2022 | 0.2150 kg CO₂e/kWh |
| 2023 | 0.1980 kg CO₂e/kWh |
| 2024 | 0.1830 kg CO₂e/kWh |
| 2025 | 0.1710 kg CO₂e/kWh |
| 2026 | 0.1580 kg CO₂e/kWh |
Data Sources
Three sources cover purchased-heat accounting. Prefer a supplier-specific factor over any of them; these are the default and screening tiers.
- UK DEFRA 2026 Conversion Factors — district heating. Combined delivered-heat factors for district and on-site heat (
district_heating.gbr.onsite/district_heating.gbr.district), each with a_wttupstream companion, plus the district-heat T&D loss factor (transmission_distribution.gbr.district_heat). AR5 GWP basis by DEFRA convention. Surfaced live in the tables above. - EUROSTAT renewable-share data + EU fossil-DH baseline. Per-country renewable-and-waste-heat share for ~30 European countries (
district_heating.<iso3>.eurostat.renewable_share) and the EU fossil district-heating baseline (district_heating.eu_framework.fossil_dh_baseline_ef= 0.215 kg CO₂e/kWh) for adjusting a default toward a network’s actual mix. - IPCC AR6 GWP-100. The GWP values for any factor derived from first principles — fossil CH₄
29.8, N₂O273. See the AR6 GWP dataset.
Error Traps
Each error below produces a specific, quantifiable distortion. Magnitudes shown against the worked examples where applicable.
| Error | What happens | Magnitude | How to avoid |
|---|---|---|---|
| Account purchased steam as Scope 1 | The supplier’s combustion is pushed into the consumer’s direct emissions. | Double-counts against the supplier’s inventory; misclassifies the whole heat line | Apply the ownership-and-operation test. You consume the heat; you don’t combust the fuel → Scope 2. |
| Use the raw fuel factor as the heat factor | Conversion loss is ignored — the fuel EF is used directly without dividing by efficiency. | Understates Scope 2 by ~15% in Example 2 (161 tCO₂e on 1,072 tCO₂e) | Divide the fuel EF by the plant efficiency: EF_heat = EF_fuel ÷ η. |
| Skip CHP allocation | 100% of a cogeneration plant’s emissions are assigned to the heat stream. | 2.5× overstatement in Example 3 (1,500 vs 600 tCO₂e); double-counts electricity consumers | Allocate combustion emissions between heat and power before deriving the heat factor. |
| Report only one Scope 2 figure | Either the location-based or market-based number is reported, not both. | Non-compliant disclosure under Scope 2 Guidance and CSRD ESRS E1-6 | Always report both. Where no contractual instrument exists, they converge on the network default. |
| Fold the WtT companion into Scope 2 | The upstream-fuel well-to-tank factor is added to the Scope 2 delivered-heat figure. | Overstates Scope 2, understates Scope 3 Cat 3 (71.54 tCO₂e in Example 1) | Keep WtT on the Scope 3 Category 3 line. The Scope 2 figure is combustion-and-delivery only. |
| Double-count delivery losses | A separate T&D loss factor is added on top of an already-delivered-basis factor. | Inflates Scope 2 by the loss percentage, typically 5–15% of the heat line | A delivered-basis factor already includes losses. Add the T&D factor only when working from a generation-basis factor. |
| Mix AR5 and AR6 bases in one total | An AR6-derived line is summed with an AR5-basis DEFRA heat line. | Small per-line error; CSRD greenwashing-disclosure risk if undisclosed | Keep one basis per total. DEFRA heat factors are AR5 by convention — disclose, don’t convert. |
Methodology Metadata — for GHG Inventory Documentation
Copy into your GHG inventory methodology statement for ISO 14064-1 transparency compliance. Adjust the factor-derivation line to the route you used.
| Methodology | GreenCalculus Purchased Steam & Heat Methodology v1.0 (June 2026). greencalculus.com/methodology/purchased-steam-heat-methodology/ |
| Scope | Scope 2 indirect emissions from purchased steam, hot water, and district heat. Reported location-based and market-based per the GHG Protocol Scope 2 Guidance. |
| Factor derivation | [Supplier-specific kg CO₂e/kWh | Efficiency method — fuel EF ÷ plant efficiency | Network default — DEFRA 2026 district-heat factor / EU fossil-DH baseline]. CHP heat allocated per the CHP cogeneration allocation methodology. |
| GWP basis | IPCC AR6 GWP-100 for corporate reporting (CH₄ fossil = 29.8, N₂O = 273). DEFRA-sourced heat factors retain AR5 GWP basis by DEFRA convention; mixed-basis values disclosed explicitly, never summed within one total. |
| Boundary components | Delivered-heat combustion factor and network delivery loss in Scope 2; upstream fuel (well-to-tank) in Scope 3 Category 3. |
| Disclosure framework | CSRD ESRS E1-6 dual Scope 2 reporting; UK SECR; SBTi Scope 2 target boundary; CDP Climate. |
| Update schedule | Factor values self-heal on each DEFRA / EUROSTAT vintage via the live MasterBrain. Methodology re-reviewed on any GWP-basis or Scope 2 Guidance change. |
Ready to compute your purchased steam and hot water emissions? Open the Purchased Steam & Hot Water Calculator →
Frequently Asked Questions
Scope 2. The test is who owns and operates the combustion equipment. If a third party burns the fuel and pipes you the steam, the emissions are indirect — Scope 2, alongside purchased electricity. Only heat from a boiler or CHP unit you own and operate is Scope 1. Accounting purchased steam as Scope 1 double-counts against the supplier’s own inventory.
Two fallbacks. If you know the input fuel and the plant’s thermal efficiency, use the efficiency method: divide the fuel’s emission factor by the efficiency (EF_heat = EF_fuel ÷ η). If you have neither, apply a published network default — the DEFRA district-heat factor in the UK, or the EU fossil district-heating baseline of 0.215 kg CO₂e/kWh adjusted by the network’s renewable share elsewhere. Document which route you took.
Yes. The GHG Protocol Scope 2 Guidance dual-reporting requirement applies to purchased heat as much as to electricity. The location-based figure uses the network or default factor; the market-based figure uses a supplier-specific factor or contractual instrument. Where no contractual claim exists, the two converge on the network default. CSRD ESRS E1-6 requires both.
Because of conversion loss. A boiler converts fuel energy to delivered heat at less than 100% efficiency — typically 80–90% for a modern gas boiler. The delivered-heat factor is the fuel factor divided by that efficiency, so it is always larger. For an 85%-efficient boiler burning natural gas at 0.18231 kg CO₂e/kWh, the delivered-heat factor is 0.18231 ÷ 0.85 = 0.21448 kg CO₂e/kWh.
Allocate first. A CHP plant produces heat and electricity from one fuel input, so the combustion emissions must be split between the two outputs before you derive a heat factor — most commonly by the energy or efficiency method. Using the plant’s unallocated fuel emissions for the heat factor overstates it, often by a factor of two or more, and double-counts against the electricity consumers. See the CHP cogeneration allocation methodology for the full mechanics.
Scope 3 Category 3 (fuel- and energy-related activities), not Scope 2. The extraction, processing, and transport of the fuel the supplier burns is upstream of combustion. The DEFRA heat factors carry a paired well-to-tank companion for this — keep it on the Scope 3 line and never fold it into the Scope 2 delivered-heat figure. Network delivery losses, by contrast, are Scope 2.
Only if the instrument meets the Scope 2 Guidance quality criteria — exclusivity, tracking, and no double-claiming — the same bar applied to energy attribute certificates for electricity. Heat instruments are less mature than electricity ones, so the most credible market-based input for heat is usually a verified supplier-specific factor for the actual plant rather than a tariff claim. Scrutinise the tracking behind any green-heat claim before relying on it.