70-year-old apartment buildings heat with geothermal energy

08.07.2025

Source: E & M powernews

An investor from Rostock has converted three apartment buildings from the 1950s in Rövershagen to geothermal energy without having to replace radiators in the apartments.

In Rövershagen, north-east of Rostock, there is a development of six apartment buildings, each with ten apartments. This type of construction, typical since the 1950s, can be found all over Germany. Three of the houses near the Baltic Sea in Mecklenburg were purchased by an investor and renovated to make them more energy-efficient. They have been heated energy-efficiently with geothermal energy for a month now, and one of the houses already meets the KfW 55 standard.

Renovation work was first carried out on the estate in the 1990s: The facades of the apartment buildings were insulated with a composite thermal insulation system. The windows, doors and roof remained as they were in the year of construction. In addition, central gas heating systems were installed in all the buildings to heat the apartments and supply them with hot water.

The concept for the heating replacement was implemented by Nibe in collaboration with Goldwasser Bohrgesellschaft mbH. Nibe is a heating technology company founded in Sweden in 1952 and named after its founder, Nils Bernerup. The Wroblewski brothers from Rostock acquired three of these apartment buildings and opted for geothermal heating, which guarantees cost-effectiveness and energy efficiency. The first step was to replace the heat generator in two of the houses and comprehensively renovate the third building to KfW 55 standard.

Heating and hot water with geothermal energy

Mathias Wroblewski explains the decision to use geothermal energy because the tenants in other buildings felt disturbed by the fan noise of the air heat pumps. The property also offered enough space to use geothermal energy as a heat source. Five boreholes, each 150 meters deep, were drilled in front of each building and fitted with geothermal probes. The front gardens can then be replanted or used for drying laundry. The underground pipes with the brine-water mixture are expected to last for a hundred years.

The gas heating systems in the basements of the two houses were replaced by brine-water heat pumps with a heating capacity of 43 kW. The heat pumps are speed-controlled so that their output automatically adjusts to the reduced heating load as soon as the energy renovation measures planned at a later date are carried out. It was not necessary to replace the radiators in the apartments for the heat pump to work effectively.

For the hot water supply, the large-scale drinking water system of the houses with
was equipped with an MTL 500 hot water storage tank, which holds 500 liters of water and has an integrated electric reheating stage. This system configuration is particularly space-saving and efficient.

KfW 55 standard

The third apartment building was completely renovated to the KfW 55 standard: The
attic was converted and two apartments were added. The building was also completely gutted and the windows and doors were replaced. The heat is distributed via underfloor heating. Mathias Wroblewski explained in an interview with this editorial team that this was only possible thanks to the favorable subsidies and low interest rates of the past: "It would no longer pay off at the moment," he said. Due to the better energy standard, a heating output of 25 kW is sufficient for heating and hot water preparation for the 12 apartments in this building, also in conjunction with a hot water tank.

The investment would be refinanced in the long term through the higher rents than in the other buildings. The operating costs there are higher due to the poorer energy efficiency, but significantly lower than the costs for oil or gas heating, said Wroblewski. "Ultimately, it all comes down to the price of electricity," which the federal government could influence through taxes, for example.

Author: Susanne Harmsen