Deutsche Umwelthilfe to challenge Germany's new heating law at Constitutional Court

The new law

The Gebäudemodernisierungsgesetz, published in the Federal Law Gazette in the last week of July 2026, replaces the earlier heating law that required every newly installed heating system to run on 65 percent renewable energy. Under the new rules, new gas and oil heaters may still be installed from 1 January 2029, provided they use a gradually increasing share of CO2-neutral fuels such as biomethane. For existing heaters, a "green gas quota" will be introduced from 2028, starting at up to 1 percent, though details remain unclear. The law also drops the previous ban on installing oil and gas heaters after 2044, a prohibition that had been part of the Building Energy Act.

Constitutional complaint

Deutsche Umwelthilfe (DUH) announced it will file a constitutional complaint against the law at the Federal Constitutional Court in Karlsruhe. Federal managing director Barbara Metz told the Deutsche Presse-Agentur that lawyer Remo Klinger is preparing the submission, with filing expected in September.

Now we know what this law looks like in its final form. Our lawyer Remo Klinger is now drafting the constitutional complaint. We will be ready to submit it to the Federal Constitutional Court in September.

Legal arguments

The complaint centres on Article 20a of the Basic Law, which obliges the state to protect the natural foundations of life, also in responsibility for future generations. Metz argued that the building sector is a substantial source of CO2 emissions and that missing climate neutrality there would jeopardise the overall target.

The most serious thing is: the goal of climate neutrality by 2045 cannot be achieved with this law. After 2044, the installation of oil and gas heaters will still be possible. That ban has fallen. It existed previously in the Building Energy Act.

Metz also criticised the so-called "bio-staircase" (Biotreppe), which requires a stepwise increase in biogas use but is only regulated until 2040.

The bio-staircase can become very expensive, because it is unclear whether these biogases will even be available. Everything beyond 2040 remains open and unclear.

Tenants, she added, have no say over which technology is installed in their buildings, leaving them exposed to unknown future costs.

Broader concerns and next steps

Other associations and experts have also raised constitutional doubts about the new law. Metz expressed confidence that the court would accept the complaint, contrasting it with an earlier unsuccessful challenge to a speed limit that targeted only a single measure.

The Building Modernisation Act, however, relates to the entire building sector with very many CO2 emissions. And it represents a clear step backwards in climate protection, which is not permissible.

The Federal Constitutional Court must first decide whether to accept the complaint for a ruling. If it does, the case could set a precedent for how far climate legislation must go to meet constitutional obligations. The timeline below shows the key dates in the law's implementation and the legal challenge.