Hamburg to Restrict Fossil Fuel Heating Systems via State Opening Clause
Münster/Hamburg – The planned Building Modernization Act (GModG) strengthens the position of fossil fuel heating technology, allowing gas and oil to remain largely unrestricted. However, Hamburg intends to counteract this trend. The SPD and Green parties in Hamburg are calling for a state opening clause that would effectively enable restrictions on fossil fuel heating systems.
The federal cabinet has initiated the Building Modernization Act (GModG). The current version replaces the 65 percent renewable energy mandate from the previous Building Energy Act with a phased blending requirement for biogas and similar fuels, known as the ‘bio-staircase.’ Hamburg considers this insufficient given its energy and climate goals. The Hamburg Parliament approved a corresponding motion from the red-green Senate parties on Wednesday (May 20, 2026), with a red-green majority and support from the Left Party. This grants the Senate a mandate to advocate at the federal level for the retention, and potentially the expansion, of the state opening clause.
GModG: Bio-Staircase Replaces 65 Percent Rule – Fossil Fuel Heating Remains Permitted
The federal cabinet approved the new Building Modernization Act on May 13, 2026. The previous requirement that new heating systems operate with at least 65 percent renewable energy is being dropped. It is replaced by the so-called ‘bio-staircase’: gas and oil heating systems will remain generally permissible but must use a gradually increasing minimum proportion of biogenic fuels or hydrogen – 10 percent from 2029, 15 percent from 2030, 30 percent from 2035, and 60 percent from 2040.
The GModG includes a state opening clause in Section 9. This clause would allow federal states to impose further requirements for renewable energy in buildings and to restrict direct electric heating systems. However, it does not directly enable states to act against fossil fuel heating systems, unless more stringent renewable energy requirements de facto exclude them. The GModG still needs to pass through the Bundestag and Bundesrat. According to the Green parliamentary group, it is not yet possible to definitively assess whether the GModG is an objection law – similar to its predecessor, the GEG 2023 – based on the current draft.
Hamburg Seeks to Secure and Expand State Opening Clause for Renewable Heat
The current design of the state opening clause is a thorn in the side of Hamburg’s Senate coalition of SPD and Greens. The parliamentary resolution mandates the Senate to advocate at the federal level for the preservation of the clause and, if necessary, to expand its scope for its own state regulations. States could then impose their own requirements for the proportion of renewable energy when replacing heating systems, which could effectively lead to restrictions on fossil fuel heating systems. At the same time, the governing factions fear that the clause could be completely removed in the Bundestag.
This initiative is set against the backdrop of Hamburg’s municipal heat planning, which relies on district heating in inner-city areas and heat pumps in decentralized areas. Approximately 40 percent of the city’s CO2 emissions originate from the heating sector, making heating system replacement a central lever for Hamburg’s 2040 climate target. SPD spokesman Alexander Mohrenberg emphasized the urgency: “Around 40 percent of the city’s CO2 emissions are generated in the heating sector. Anyone who wants to achieve Hamburg’s climate goals must make consistent progress here. This must not be jeopardized by the new Building Modernization Act.” Melanie Nerlich, energy policy spokeswoman for the Greens, added: “To suggest to people today that a new gas heating system is a good idea is misleading consumers. […] The state opening clause gives us precisely this important freedom, which is why we want to maintain it in the future.”
Source: IWR, 2026
