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Helsinki’s energy company Helen plans to route waste heat from an OnZero data centre built for AI workloads into the city’s district-heating network, with heat recovery scheduled to begin in 2027. Helen estimates the project could supply more than 500,000 MWh of heat a year—an amount it compares with the annual heating needs of around 70,000 flats. That is a projection, not a count of homes already receiving heat.
What Helsinki and OnZero have announced
Helen and OnZero announced an agreement on 31 August 2026 to connect a planned OnZero data centre in Helsinki to Helen’s district-heating network. OnZero calls the facility an “AI Heat Factory”; Helen says heat recovery is scheduled to begin in 2027. The announcements describe a planned project, not an operating facility or measured heat delivery. Helen’s announcement and OnZero’s announcement both give the scale as roughly enough heat for 70,000 apartment homes or flats.
The projected annual output is presented slightly differently by the two partners:
| Source | Projected annual heat | Equivalent | Status of figure |
|---|---|---|---|
| Helen, 31 August 2026 | More than 500,000 MWh | Heating needs of around 70,000 flats | Company estimate for the planned project |
| OnZero, 31 August 2026 | Up to approximately 525,000 MWh | Approximately 70,000 apartment homes | Company estimate for the planned project |
These are not two independently verified readings, nor does either announcement define a fixed number of households that will be connected. “70,000 homes” is an annual heat-demand comparison: it does not mean 70,000 named households are customers or that each will receive heat directly from the data centre.
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How can an AI data centre heat homes?
Servers use electricity, and their operation produces heat. Instead of rejecting all of that heat to the surroundings, a recovery system can capture it and transfer it into a district-heating network. Helen’s data-centre heat-recovery service description says heat pumps raise the recovered heat to a level suitable for transfer to its energy platform and onward into the network. The network then distributes heat to connected buildings.
The arrangement depends on location: Helen says a data centre must be close enough to the district-heating network for its heat to be useful to homes. Its service description discusses a configuration where heat supplied to the network is approximately 85°C, but the OnZero announcement does not specify that temperature for this project. It should not be assumed to describe the new facility’s design.
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Helen’s chief operating officer Tuukka Toivonen summarized the proximity requirement in a 10 September 2025 announcement: “The electricity they use always turns into heat, which can then be used to heat homes – as long as they are located close enough to the district heating network.” In the quotation, “they” refers to data centres. Helen’s explanation of data-centre integration provides that context.
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Helen says heat recovery is scheduled to start in 2027. The 31 August 2026 announcements establish the agreement and planned start, but do not establish construction progress, commissioning, actual annual delivery, or uptime. The 500,000-to-525,000 MWh range should therefore be read as a projected scale, not a result already achieved.
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Helen COO, Strategy and M&A, Tuukka Toivonen said the project could “reduce the need for combustion-based heat production in a cost-effective way” while keeping district heating competitive and attractive. That is Helen’s stated rationale; the announcements do not include an independent lifecycle-emissions assessment or quantified emissions savings for OnZero.
How this compares with Helsinki’s other data-centre heat projects
Helen has described earlier data-centre heat-reuse projects in Helsinki. They provide local context, but their output figures should not be treated as evidence of what OnZero will deliver: the sites, project stages, and household-equivalent descriptions differ.
| Project | Heat figure and equivalent | Status or qualification |
|---|---|---|
| OnZero data centre | Helen estimates more than 500,000 MWh per year for around 70,000 flats; OnZero says up to approximately 525,000 MWh for approximately 70,000 apartment homes | Planned; recovery scheduled for 2027. Partner estimates, not operating measurements. |
| Telia Helsinki Data Center, Pitäjänmäki | After an expansion, up to 14,000 two-room-apartment equivalents; a future plan aims to reach 28,000 | Helen’s 26 May 2025 announcement describes this separate Telia project. Its undated service page says up to 90% of that centre’s waste heat is recovered; that figure is specific to Telia and is company-published. |
| Elisa data centre, Pasila | Up to 1,000 one-bedroom-flat equivalents | Described in Helen’s 10 August 2022 announcement about the Elisa project. |
The Telia expansion and future target are described in Helen’s 2025 announcement; the 90% description appears on Helen’s service page. The Pasila project is covered in Helen’s 2022 announcement. Because “two-room apartment,” “one-bedroom flat,” and “flat” are not a single standardized unit, the household-equivalent labels matter as much as the headline counts.
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A useful assessment once the project is operating would separate design expectations from delivered heat. Readers comparing announcements or later performance reports should look for:
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- Annual heat actually delivered: measured MWh over a stated period, rather than a design estimate or maximum.
- Project status: whether the site is announced, being built, commissioned, or operating.
- Equivalent basis: whether the comparison is to flats, apartment homes, or a defined dwelling type, and what annual heat demand underlies it.
- Recovery details: the heat-pump and network arrangement, including relevant operating conditions and proximity to the network.
- Emissions evidence: a stated method and boundary for any claimed emissions reduction, rather than assuming that heat recovery alone establishes lifecycle savings.
The 2026 partner announcements do not provide independent measurements of OnZero’s heat output or an independent lifecycle-emissions assessment.
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