Energy and Heating Duties in 2026: GModG, Energieausweis, CO₂ Split
Tenancy law and the owners association · Stand: 2026-08-10
The GModG replaced the GEG. The Gebäudemodernisierungsgesetz passed Bundestag and Bundesrat on 10 July 2026, appeared in the Bundesgesetzblatt on 28 July 2026, and its first provisions took effect on 29 July 2026, with further stages to follow.
The 65% renewables rule is gone. New heating systems no longer have to run 65% on renewables. Instead a "Bio-Treppe" obliges new fossil-fuelled systems to use a rising share of biogenic or synthetic fuel: reportedly 10% from 2029, 15% from 2030, 30% from 2035, 60% from 2040, climate-neutral by 2045. Implementing details are still being fleshed out – verify the exact staging before making an investment decision. There is no obligation to replace a working heating system.
Kommunale Wärmeplanung: large cities such as Bonn were due to complete their heat plans by 30 June 2026, smaller municipalities by 30 June 2028. Under the GModG the plan no longer directly triggers owner obligations, but it tells you whether Fernwärme is coming to your street – which is exactly what decides whether a heat pump is sensible.
Energieausweis. Still mandatory on sale and on new letting. Show it to prospects at the viewing at the latest, hand over a copy at contract signature, and quote the mandatory data (type, energy value, energy source, efficiency class, construction year) in every listing. Valid 10 years; fines up to €10,000. The GModG digitises and expands it, with reports pointing to phase-in from 2027. For a flat, the certificate covers the whole building – get it from the Verwalter.
CO₂ cost split. The Kohlendioxidkostenaufteilungsgesetz (CO2KostAufG) splits the carbon price by how bad the building is:
| kg CO₂/m²/year | Tenant | Landlord |
|---|---|---|
| < 12 | 100% | 0% |
| 12 – <17 | 90% | 10% |
| 17 – <22 | 80% | 20% |
| 22 – <27 | 70% | 30% |
| 27 – <32 | 60% | 40% |
| 32 – <37 | 50% | 50% |
| 37 – <42 | 40% | 60% |
| 42 – <47 | 30% | 70% |
| 47 – <52 | 20% | 80% |
| ≥ 52 | 5% | 95% |
You must calculate this in the Heizkostenabrechnung and show the classification and basis; fail to, and the tenant may cut their heating share by 3% (§7(4)). New §5a CO2KostAufG adds a 50/50 split of gas network charges and CO₂ costs from 1 January 2028, and of the mandatory bio-fuel premium from 2029, for systems installed under §43 GModG – a genuine new landlord cost, worth tracking.
Verified Primary Sources:
- §Energieausweis: Pflichten, Kosten und Änderungen 2026(ADAC, 2026-08)
- §CO2KostAufG §5a – hälftige Aufteilung ab 2028/2029 (neu durch GModG)(Bundesministerium der Justiz / juris, 2026-08)
- §CO2KostAufG – Anlage: Zehn-Stufen-Modell(Bundesministerium der Justiz / juris, 2026-08)
- §Gebäudemodernisierungsgesetz: Chronologie und Inhalte(GEG-Infoportal des Bundes, 2026-08)