What OnZero and Helen Agreed To
OnZero, an Austrian-Finnish developer of AI data centres, signed an agreement with Helen, the municipal energy utility that heats most of Helsinki, to connect a new liquid-cooled AI computing facility to the city's district heating network. The deal was disclosed on September 1, 2026, in a press release distributed through EQS News, and covered separately by Data Center Dynamics and the Italian outlet BeBeez.
Under the arrangement, OnZero will capture the heat its servers generate and pipe it into Helen's existing district heating infrastructure, the same network of insulated pipes that already carries hot water to apartments, offices, and public buildings across the city. Helsinki has run a district heating system since the 1950s, and roughly nine in ten homes in the city already draw on it, which gives OnZero a ready customer base rather than a network it has to build from scratch.
The Numbers Behind 525,000 MWh
The recovered-heat volume in this agreement reaches up to 525,000 MWh a year, a figure OnZero and Helen say is equivalent to heating around 70,000 apartments. That comparison only works because Helsinki's winters demand a steady, predictable heat load, and a data centre running continuously can supply exactly that, unlike solar or wind heat sources that fluctuate with the weather.
| Metric | Figure |
|---|---|
| Recovered heat supplied to the district network | Up to 525,000 MWh per year |
| Equivalent apartments heated | Roughly 70,000 |
| Heat capture rate | Up to 99% |
| On-site water used for cooling | Zero (no evaporative cooling) |
| Planned start of operations | 2027 |
A 99% capture rate is unusually high for a data centre of any kind, and it is only achievable because the facility uses direct liquid cooling rather than air handling units, which lose most of their heat to the outside air instead of a usable pipe.
A Pre-Emptive Answer to Europe's Water Scrutiny
The zero-water cooling design answers a regulatory pressure that has already slowed AI data centre growth elsewhere in Europe. Ireland's grid operator has restricted new data centre connections around Dublin for several years, in part over resource strain concerns, and the Netherlands has imposed its own moratoria on new hyperscale sites while it works out national siting criteria.
Evaporative cooling, the technology this design avoids entirely, is the part of a data centre's footprint that draws the most public and regulatory attention, because it consumes municipal water supplies a city also needs for drinking and sanitation. By using a closed liquid loop instead, OnZero removes water from the list of objections a planning authority or a community group can raise against the project, before that objection is even filed.
What a Data Centre Buyer Should Take From This
A company siting or buying capacity in an AI data centre now has a concrete precedent for demanding a heat-reuse clause in its own contract. That clause would need three things this deal already has: liquid cooling capable of capturing heat at usable temperature, physical proximity to a district heating network with spare capacity, and a utility willing to sign a long-term offtake agreement for the recovered heat.
The commercial upside is real but should not be overstated. Selling 525,000 MWh a year of heat generates revenue or a cost offset for OnZero, though the exact tariff Helen pays was not disclosed, so the precise euro value of that offset against the facility's own power and cooling bill is not yet public. What is public is the structural point: heat that used to be vented as waste is now a second product line, and any operator that cannot capture and sell it is leaving that line on the table.
The 'AI Heat Factory' Blueprint for Europe
OnZero positions the Helsinki project as a reference deployment for what it calls its 'AI Heat Factory' model, a design it says it intends to repeat at other European sites. The company frames the model less as a green add-on and more as the default shape a large AI data centre should take once it sits near a city with district heating infrastructure already in the ground.
Helsinki gives OnZero a strong first reference precisely because Helen's network is large, mature, and already priced into the city's energy planning, which makes the technical case easier to prove and the commercial case easier to repeat in Stockholm, Copenhagen, or Vienna sized cities with similar district heating coverage.
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