How to build a rental‑income stress‑test for 2027 CO₂ pass‑throughs

What the law now requires — the datapoints you must collect

Start with primary documents: the Heizkostenverordnung (HeizkostenV) requires that consumption meters installed after 1 December 2021 are remote‑readable and sets an implementation deadline for existing devices; where a building owner has not installed required remote‑readable equipment the tenant may reduce the billed share by 3 % under the statutory provision added to § 12. Collect the building’s itemised Nebenkosten (operating costs) and specifically extract the annual heating and hot‑water cost lines for the years 2022, 2023 and 2024 — these three years are treated in the amended rules as the baseline reference for some tenant information and evaluations. ([gesetze-im-internet.de](https://www.gesetze-im-internet.de/heizkostenv/HeizkostenV.pdf?utm_source=openai))

Which CO₂ price to use for 2027: law, draft and publication route

Two laws determine how a landlord must reference a CO₂ certificate price in tenant billing rules. The CO2‑cost‑allocation law (CO2KostAufG) fixes how the “relevant certificate price” is derived: for 2027 the law ties the figure to the average of BEHG auction prices published for the prior period (the Umweltbundesamt is the publication point). Separately, amendments to the BEHG created a statutory mechanism for a price corridor; the government used a €55–€65/ton corridor for 2026 and drafts from the responsible ministry have stated a policy intent to apply a €55–€65/t corridor also for 2027 (this latter source is a ministry draft and therefore not a final, binding number). For stress‑testing, you can model both: (a) statutory route where 2027 uses the average auction price as published by the UBA; and (b) an explicit corridor scenario of €55/t and €65/t to show downside and upside. ([gesetze-im-internet.de](https://www.gesetze-im-internet.de/co2kostaufg/BJNR215400022.html?utm_source=openai))

Step‑by‑step stress‑test (spreadsheet workflow)

1) Baseline Nebenkosten: compute the three‑year average of total annual heating + hot‑water costs (2022–2024) from your Betriebskosten lines (BetrKV lists which items may appear in Nebenkosten). This is your contractual baseline for operating‑cost comparisons. ([gesetze-im-internet.de](https://www.gesetze-im-internet.de/betrkv/BJNR234700003.html?utm_source=openai))

2) Prepare consumption or energy‑input data per property: preferably actual billed fuel volumes or metered kWh for each account. If you only have cost lines, keep them but annotate that you lack physical consumption data — this increases model uncertainty.

3) Convert consumption to CO₂ emissions: multiply fuel quantity by the appropriate emissions factor (kg CO₂ per kWh or per litre) or, for district heating, use the network’s heat‑value‑weighted emission factor where the CO2KostAufG requires a single network factor. Do not invent emission factors—obtain them from the supplier, the utility’s emissions statement or the UBA/contract text. ([gesetze-im-internet.de](https://www.gesetze-im-internet.de/co2kostaufg/BJNR215400022.html?utm_source=openai))

4) Apply certificate price scenarios: compute incremental cost = emissions (t CO₂) × price (€/t). Run at least three columns: €55/t, €60/t, €65/t; and a fourth column using the official UBA‑published 2027 average when it appears (per CO2KostAufG). ([gesetze-im-internet.de](https://www.gesetze-im-internet.de/co2kostaufg/BJNR215400022.html?utm_source=openai))

5) Map pass‑through to tenant charge: follow the legal allocation rules — agreements that make tenants pay more than their statutory share are ineffective. Show the incremental € per flat and as a percentage of baseline Nebenkosten and of expected net rental income. ([gesetze-im-internet.de](https://www.gesetze-im-internet.de/co2kostaufg/BJNR215400022.html?utm_source=openai))

6) Sensitivity and liquidity: stress rental cashflow for 12‑ and 24‑month lags (late tenant payment, delayed billing disputes) and include a scenario where required remote‑metering is missing and tenants exercise the 3% reduction. Add an operating‑cost uplift to reflect possible additional O&M or supplier fees for remote‑readable installations disclosed under FFVAV rules for district heat. ([gesetze-im-internet.de](https://www.gesetze-im-internet.de/heizkostenv/HeizkostenV.pdf?utm_source=openai))

Practical red flags and next steps

Red flags to stop work: the utility cannot provide a network emission factor (for district heat); you lack consumption data for the property; meters are not remote‑readable and the owner has not budgeted for retrofits. If any of these occur, the landlord’s ability to pass CO₂ costs to tenants becomes uncertain and tenant disputes are likely.

Next steps: prepare the spreadsheet, seek the UBA average auction price when published for 2027 and document every contractual basis (heat supply contract, Hausgeld/WEG minutes, lease clauses). For legal questions about lease enforceability or for tax treatment of recovered costs consult a German lawyer and a tax adviser. This article is a methods guide, not personalised legal, tax or investment advice. ([gesetze-im-internet.de](https://www.gesetze-im-internet.de/co2kostaufg/BJNR215400022.html?utm_source=openai))