Summary
- Waste-heat recovery from the OnZero facility is scheduled to begin in 2027.
- Helen says the project could provide more than 500,000MWh of heat each year at full scale.
- The utility has used data centre waste heat in Helsinki’s district-heating system since 2010.
Helen has agreed to connect waste heat from a new OnZero data centre into Helsinki’s district-heating network, with recovery due to begin in 2027.
The Finnish energy company said the planned facility could provide more than 500,000MWh of heat to the network each year when fully operational. Helen equates that output to the annual heating requirement of around 70,000 flats.
The companies have not disclosed the data centre’s IT capacity, electrical load, detailed thermal design, or the investment required to connect it to the heat network. Those omissions limit any direct comparison between the amount of electricity consumed by the facility and the useful heat ultimately delivered.
What is clear is the intended scale. If the full annual heat figure is reached, the scheme would move beyond the small demonstration projects often associated with data centre heat reuse and become part of Helsinki’s wider heat-supply system.
Heat recovery moves into system planning
Helen has been using recovered data centre heat in Helsinki since 2010, giving the utility operating experience with an integration problem that is increasingly appearing in new European data centre schemes.
The attraction is straightforward: servers and supporting electrical equipment ultimately reject much of the electricity they consume as heat. Capturing that energy can reduce the amount of separate heat generation required elsewhere, provided the recovered heat can be delivered at a temperature, location, and time that matches the district-heating system.
The practical conditions are less simple. Heat may need to be upgraded before entering the network, while pumps, heat exchangers, pipework, controls, and redundancy arrangements have to be incorporated without compromising the data centre’s own cooling resilience. The commercial structure also has to account for periods when either the data centre load or the heat demand differs from design assumptions.
Helen has not disclosed the detailed plant arrangement for the OnZero connection, so the scale and energy requirement of any heat-pump system cannot yet be assessed.
The project nevertheless fits a broader European shift from treating waste heat as a sustainability add-on towards designing it into the local energy system. atNorth, for example, is planning to send surplus heat from its DEN02 campus into neighbouring greenhouses from 2028, while other schemes are testing connections to municipal heating networks.
Helsinki targets less combustion
For Helen, the agreement forms part of a larger change in the way the city is heated. The utility’s 2026 climate transition plan says it intends to concentrate on data centre waste heat in the medium term and phase out combustion-based energy production by 2040.
That transition shifts part of the heating system towards electricity. Large heat pumps and other electrified heating assets can reduce direct combustion, but they also increase the importance of transmission capacity, electricity prices, and grid investment. Helen itself identifies sufficient electricity-network capacity as an important condition for its longer-term climate plans.
Data centre heat therefore sits on both sides of the electricity system. The facility creates a substantial electrical load, but the heat rejected by its computing equipment can displace some separate heat production if the recovery system is technically and commercially viable.
The quality of that trade-off depends on the project design rather than the existence of a heat-reuse agreement alone. Useful measurements will include how much heat is actually recovered through the year, the electricity consumed in upgrading and moving it, the temperature supplied to the network, and whether the data centre can maintain the expected heat output as its IT load changes.
OnZero and Helen now have until the planned 2027 start of recovery to turn the agreement into operating infrastructure. The eventual annual heat delivered — rather than the maximum potential figure — will determine how substantial a contribution the data centre makes to Helsinki’s changing district-heating mix.
