Zenne River powers Belgium’s first large-scale aquathermic heating system
The National Social Security Office (RSZ) has commissioned a pioneering heat pump system that uses water from the Zenne River to heat its Horta building at Brussels’ Gare du Midi. This feat is a first of its kind in Belgium in terms of scale, temperature capacity and location above a river.
Renewable energy replaces gas
The two pumps, with a combined capacity of 1,400 kilowatts, enable the entire RSZ headquarters to be heated without gas. The aquathermic system cuts CO₂ emissions by 361 tonnes per year and saves around 150,000 euros annually in energy costs. “Gas is no longer necessary to heat our building. We now meet our needs with local renewable energy,” said Koen Snyders, general director of RSZ.
The installation operates by pumping and degassing water from the Zenne to produce heat with an efficiency four times higher than that of a conventional boiler. The water returned to the river is, on average, only 0.1°C cooler, a change that “even improves the oxygen content, according to Leefmilieu Brussel, which issued the necessary permits,” the RSZ notes.
© BELGA VIDEO MATEUSZ KUKULKA
Technological first for Brussels
Developed in collaboration with Veolia, which handled the design, construction and maintenance, the system can reach temperatures of up to 80°C. “This installation demonstrates that technological innovation can go hand in hand with concrete impact,” said Franck Arlen, CEO of Veolia Belgium & Luxembourg. “The project also aligns perfectly with Veolia’s GreenUp strategy, in which we focus on efficient, renewable solutions that help our partners become carbon-free.”
The project’s 20-year payback period is significantly shorter than that of comparable technologies, such as air-to-water heat pumps, which would cover only 90 per cent of heating needs and take nearly twice as long to recoup costs.
Since 2024, the RSZ’s heating network has been connected to that of the Brussels-South station, allowing the two public buildings to support each other in case of an outage or energy peak. This connection has already proved its worth: when gas boilers at the station failed in early 2025, the RSZ supplied one megawatt of heat to maintain operations.
RSZ, Veolia and NMBS are now exploring further synergies, including shared use of solar energy and connections to other sustainable sources. “This project truly demonstrates how we can modernise our public buildings while simultaneously increasing our energy independence,” said minister for the economy, employment and agriculture, David Clarinval. “It shows that it’s possible to combine efficiency, sustainability and modernisation, and it fits into a vision of a more resilient government that respects our climate goals.”
Deputy prime minister and minister of social affairs Frank Vandenbroucke added: “I’m quite proud that our National Social Security Office is moving away from gas heating today. Everyone who chooses this option makes our country a little less dependent on extremists like Putin. Fossil-free heating is not only good for the climate but also for our health — lower emissions mean cleaner air and fewer illnesses. Our next step is clear: a heat pump must become the most affordable option for every family.”
A new heating system, using a heat pump system involving the water of the Zenne River, is presented at the offices of the ONSS - RSZ in Brussels on Wednesday 22 October 2025. © BELGA PHOTO MATEUSZ KUKULKA
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