In the basement of Schöppinger Straße 18 in Berlin-Lichterfelde it is sometimes cosy warm. Klara Geywitz stands next to a floor-to-ceiling grey container to which various sensors are attached. Grey plastic pipes run along the walls and under the ceiling, a subtle hum fills the room. The SPD building minister seems satisfied. "It's very quiet," she says, looking at the heat pump that supplies five apartment buildings belonging to the Märkische Scholle cooperative from this basement. "Many people think they are such small steam locomotives." No, no, says Jochen Icken, chairman of the cooperative. Only a little more than 40 decibels have devices like this, which hardly disturbs.

Julia Löhr

Business correspondent in Berlin.

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A date like this would hardly have interested anyone a few years ago. But since the draft by Economics Minister Robert Habeck (Greens) and Geywitz for the reform of the Building Energy Act (GEG) has been in the world, heat pumps have become a highly political issue. Which is why Geywitz is surrounded by cameras and microphones in the basement. From next year, at least according to the plan, no new oil or gas heating systems should be allowed to be installed in Germany. The heating system of the future should be the heat pump, CO2-neutral operated with green electricity. FDP, homeowners and also parts of the SPD have criticized the plans with some harsh words. Geywitz's appointment in Lichterfelde-Süd is therefore also a statement: It's possible.

A huge investment

Works, but only with a lot of money, nerves and idealism, one must add. According to its own information, the cooperative has invested 100 million euros in the renovation of the quarter with around 800 apartments, which was built in the thirties, and the subsidies from KfW have already been deducted. There was better insulation, solar systems on the roof, energy storage and several brine-water heat pumps, which are considered the Porsche of heat pumps: particularly efficient because they use heat from the ground, but also particularly expensive because of the complex installation.

For a cooperative with an annual turnover of 17 million euros, the renovation was a huge investment, partly financed by equity, partly by loans. Icken explains why he still thinks there is no alternative: "Because I have grandchildren. They should also have something of the world."

On the whole, everything went well, says the head of the cooperative. Initially, they had "collected" vacant apartments in the settlement, into which tenants could then move during the renovation of their house. According to Icken, the heat pumps run largely without problems. However, the tenants in the apartments would no longer come as before to a maximum of 26 degrees, but only to 21 to 23 degrees. In the beginning, not everyone liked that. "The question of the comfortable temperature is also a matter of getting used to," comments Geywitz. Hot water preparation was also a challenge. To save electricity, the system is set to 50 instead of the usual 60 degrees. A special filter system was installed against the formation of Legionella. Getting this approved by the health department was quite difficult, reports Icken.

By 2 euros per square meter, the cooperative has raised the cold rent after the renovation, the modernization apportionment so feared by tenants. With an average cold rent of 7 euros per square metre and 1.80 euros for operating costs, the rent is still moderate by Berlin standards. After just under an hour, the tour is over, and Geywitz takes a seat in the neighbourhood centre of the Märkische Scholle. It is about the coalition committee on Sunday and the question of what a compromise on the GEG amendment could look like. Geywitz says that there are not only heat pumps, but also wood pellets, biomass, hydrogen-compatible gas heating systems, district heating, in short: a solution for each individual case.

Whether the amendment will actually come in 2024, she leaves open. "The more money you have for funding, the faster you can do it." And she also answers Robert Habeck's displeasure with the stalemate in the Progressive Coalition succinctly, but tellingly. There had already been much discussion about the Chancellor's communication. "I wouldn't advise Robert Habeck to communicate like Olaf Scholz in the future."