Two multi-family buildings in Dortmund, Germany, recently replaced their gas-powered boilers with a Vaillant propane (R290) heat pump system with a total heating capacity of 80kW (22.7TR).
The installation, completed by German contractor Alois Müller, serves two apartment buildings, each containing 10 residential units and approximately 720m2 (7,750ft2) of living space. To meet this demand, the system uses a six-unit cascade of Vaillant heat pumps, the aroTHERM plus VWL 125/8.1, installed behind the buildings. Additionally, the system includes two 800L (211gal) buffer tanks. To ensure “stable and efficient operation even at low outdoor temperatures,” the unit is equipped with the eloBLOCK VE 14 auxiliary heater.
Operating at a seasonal performance factor (SPF) of at least 3.5, the technology showcases efficiency and stability. SPF measures the efficiency of a heat pump over an entire season, defined as the ratio of total heat output to electricity consumed.
Vaillant’s modular “plug and heat” system is industrially prefabricated and delivered ready for connection. This cuts down the installation time for installations in buildings.
“For the energy transition in the multi-family housing segment, we need economically viable concepts that can be implemented quickly and easily – especially in existing buildings and without interventions in the living areas,” said Thorsten Baude, Key Account Manager for the Housing Industry at Vaillant, in a press release.
Decarbonization strategy
The buildings are managed by the Dortmund Housing Association, which initiated the project after one of the building’s boilers failed. Propane heat pumps were chosen to help drive the association’s decarbonization goals and are forecast to reduce CO₂ emissions by 20.5 metric tons annually.
“This project makes a valuable contribution to achieving our climate goals and supports the company’s long-term decarbonization strategy,” said Samuel Šerifi, spokesperson for the management board at the Dortmund Housing Association.
Similar installations
In February 2025, German food retailer ALDI stated that it would roll out Vaillant’s R290 heat pumps for space heating in the U.K. and Ireland. Up to five 12kW (3.4TR) aroTHERM plus units will be installed at each store as part of a plan to boost the company’s sustainability. As of February 2025, 226 of ALDI’s 1,000 stores in the U.K. and Ireland were equipped with Vaillant’s R290 heat pumps, with the company planning to complete the retrofit by 2030.
Moreover, R290 heat pumps from Viessmann Climate Solutions, a division of Carrier Global Corporation, are also being used to decarbonize the U.K.’s building stock. The company announced in January that its Vitocal 150-A and 250-A Pro, along with Carrier’s AquaSnap 30AWH-P and 61AQ, will be part of a £1.6 billion ($2.15 billion/€1.85 billion) procurement program to decarbonize heating in U.K. public housing and other publicly owned buildings. The selected heat pumps range in capacity from 2.1 to 105kW (0.6 to 30TR).
Outside of the U.K., Italian HVAC manufacturer Enerblue reduced the CO2 emissions of a German railway maintenance hub by 90% after replacing its gas heating unit with one of its heat pumps. The 900kW (255.9TR) air-to-water propane (R290) heat pump system reduced the annual emissions of the 27,000m2 (290,630ft2) facility by 672 metric tons.
