How to stress‑test a German buy‑to‑let for 2027 CO₂ and district‑heat risk

What official sources say — the legal anchors you will use

You will use three official data sources: the Brennstoffemissionshandelsgesetz (BEHG) for the CO₂ price mechanics and reporting timelines; the Wärmeplanungsgesetz (WPG) for municipal heat‑planning data (network maps, zones, planned expansions); and the federal ministry material on Fernwärme transparency (the Wärmenetzpaket and the draft AVBFernwärmeV reforms) for supplier price and CO₂‑intensity publication requirements. BEHG gives the historical fixed prices (2021: €25; 2022: €30; 2024: €45; 2025: €55) and establishes the 2026 price corridor (min €55, max €65); for 2027 BEHG §10(4) makes the supply price reference market‑based, tied to EU ETS auction averages unless a different rule is issued. ([gesetze-im-internet.de](https://www.gesetze-im-internet.de/behg/BJNR272800019.html))

The WPG requires municipalities to prepare Wärmepläne and makes the federal ministry responsible for central publication of result data (publication first six months after the statutory deadlines); the WPG and its draft novellings also foresee structured data transmission so municipalities’ published datasets can be harvested centrally. The federal Wärmenetzpaket/AVBFernwärmeV drafts set out that suppliers must publish prices, tariff structures and structural parameters on a national transparency platform, updated at least annually. Use these three official sources as the data backbone. ([gesetze-im-internet.edge.juris.de](https://www.gesetze-im-internet.edge.juris.de/wpg/BJNR18A0B0023.html?utm_source=openai))

Exact fields to pull (official documents and where to get them)

From the property: • Energy Performance Certificate (Energieausweis) — extract: "Endenergiebedarf" or "Endenergieverbrauch" (kWh/a), heating fuel type (Gas / Oil / Fernwärme), and reference period or measurement year. • Last 12 months’ utility bills (or Heizkostenabrechnung) — monthly consumption (kWh or m³) and billed cost components. These are your base consumption fields. (Source: property documents required in building sale/due diligence.)

From BEHG text and attachments: • The legal CO₂ price rule to apply for 2027 (BEHG §10) — you must pull the statutory reference to which market price to use for each quarter in 2027 and any ministerial implementing regulation. • The standard emissions factors for fuel types — use the factor sets listed in BEHG Anlage 1 (apply the factor that matches the fuel named on the Energieausweis). Do not substitute a number; use the factor published in the law/annex. ([gesetze-im-internet.de](https://www.gesetze-im-internet.de/behg/BJNR272800019.html))

From municipal Wärmeplan (published by the municipality or centrally by the federal ministry): • Current share of buildings in the plan area supplied by Wärmenetze (%) or absolute connected load (MW). • Planned network extension (km) and target years for new connections or fuel switching. • Designated Wärmeversorgungsgebiete (polygons or addresses). If the plan omits a numeric field, record ‘missing’ and ask the Plan‑owner; WPG requires publication of result data. ([gesetze-im-internet.edge.juris.de](https://www.gesetze-im-internet.edge.juris.de/wpg/BJNR18A0B0023.html?utm_source=openai))

From the Fernwärme transparency platform or supplier price sheets (once published under the Wärmenetzpaket / AVBFernwärmeV): • Tariff per kWh or €/MWh (base energy), fixed monthly/standing charge, connection charge, billing unit (kWh or MWh). • Reported CO₂ intensity of the supplied heat (gCO₂/kWh or tCO₂/MWh) and the reporting year. • Any contractual indexation rules (formula text) and notice periods for tariff changes. The draft reforms require these fields to be published. ([bundeswirtschaftsministerium.de](https://www.bundeswirtschaftsministerium.de/Redaktion/DE/Pressemitteilungen/2026/08/20260826-eckpunkte-waermenetzpaket.html?utm_source=openai))

Spreadsheet template and exact checks (copy these formulas)

Set up a workbook with five sheets: INPUTS, BEHG, WÄRMEPLAN, FERNWÄRME, SCENARIOS.

INPUTS — mandatory columns per building unit: Property ID | Energieausweis_kWh_pa | Fuel_Type | Measured_kWh_last12 | Billing_€/last12 | Connection_to_district_heat (Yes/No) | Address.

BEHG sheet: record BEHG source text and the CO₂ price you will apply to 2027. Do not invent the price — either: (A) enter a ministerial published 2027 reference if available, or (B) pull the EU‑ETS auction average for the quarter required by BEHG §10(4) and paste it into cell BEHG!B2. Use a named cell CO2_PRICE_2027 = BEHG!B2. (Source: BEHG §10.) ([gesetze-im-internet.de](https://www.gesetze-im-internet.de/behg/BJNR272800019.html))

Core formulas (example column formulas): - Emissions_tCO2 = INPUTS!Measured_kWh_last12 * EMISSION_FACTOR_tCO2_per_kWh (pull factor from BEHG Anlage 1 into BEHG sheet; reference that cell). Do not guess the factor value. (Use consistent units.) - CO2_cost_€/yr = Emissions_tCO2 * CO2_PRICE_2027 - If Connection_to_district_heat = Yes then Supplier_CO2_tCO2 = Measured_kWh_last12 * Supplier_CO2_intensity (from FERNWÄRME sheet). Compare Emissions_tCO2 (fuel) vs Supplier_CO2_tCO2 to highlight differences.

Checks you must run (fail = raise a red flag): 1) Energy bill reconciliation: abs(Measured_kWh_last12 − Energieausweis_kWh_pa) / Energieausweis_kWh_pa > 0,15 → flag (consumption mismatch > 15 %). 2) Missing supplier CO₂ intensity: if Connection_to_district_heat = Yes and FERNWÄRME.Supplier_CO2_intensity is blank → flag; supplier transparency should provide it. ([bundeswirtschaftsministerium.de](https://www.bundeswirtschaftsministerium.de/Redaktion/DE/Pressemitteilungen/2026/08/20260826-eckpunkte-waermenetzpaket.html?utm_source=openai)) 3) Price‑sensitivity: create scenario rows CO2_PRICE_LOW / BASE / HIGH where BASE = CO2_PRICE_2027, LOW = 0,5×BASE, HIGH = 2×BASE (or use 55 €–65 € band for sensitivity if you prefer). Calculate tenant‑cost impact as CO2_cost_€/yr divided by number of letting units and as €/m² to compare to typical rent levels. 4) District‑heat tariff shock: if Supplier €/MWh increases by > 10 % in scenario → recompute landlord pass‑through exposure (see SCENARIOS sheet).

Document every assumption in a 'metadata' cell (which source and download time). Official datasets and laws change — record the URL and the download date for traceability.

Scenarios, legal limits and next steps

Run at least three scenarios: (A) regulatory‑baseline: CO₂ price equal to the ministerial/BEHG reference for the relevant 2027 quarter; (B) high‑price: EU‑ETS surge (×1.5–2); (C) district‑heat shock: supplier tariff +20 % and supplier CO₂ intensity unchanged. Produce per‑unit and per‑m² impact tables and a cash‑flow sensitivity Tornado chart.

Two important legal cautions: (1) BEHG sets how CO₂ for fuels is priced and reported and specifies how the 2027 reference price is to be determined — but it does not itself decide whether or how a landlord may pass CO₂ costs to tenants; consult counsel or a tax adviser about tenant pass‑through rules. (2) The Fernwärme transparency platform and WPG central publication obligations are legally driven, but implementation timing and the exact downloaded fields depend on the implementing regulations and supplier uploads — always record the download timestamp and the precise field names you received. ([gesetze-im-internet.de](https://www.gesetze-im-internet.de/behg/BJNR272800019.html))

Operational next steps: 1) Download the Energieausweis and 12‑month bills and populate INPUTS. 2) Pull the municipal Wärmeplan PDF/JSON from the federal central index (or municipal website) and extract connection %, planned extension and polygons. 3) Pull the supplier price sheet or the federal transparency entry; if CO₂ intensity is not present, request it in writing. 4) Run scenarios and keep all source URLs and timestamps with the workbook. If data are missing or legal pass‑through is unclear, instruct the buyer to get a German energy lawyer and a tax adviser; this article explains measurement but is not legal advice.