Helsinki Turns AI's Biggest Problem Into Heat For 70,000 Homes

If we follow a single unit of electricity through Helsinki’s newest bet on clean heat, it comes off a Finnish grid that runs largely on nuclear, wind, and hydropower. The electrons enter a data center, where they fuel the chips that run artificial intelligence. But cooling fans do not blow the wasted heat into the air; rather, it leaves the building as hot water, traveling through insulated pipes before it warms people’s homes.

That is the arrangement OnZero, a Vienna-based data center developer, and Helen, the City of Helsinki’s energy company, signed on Aug. 31. OnZero will build what it calls an “AI Heat Factory” in Helsinki, expected to deliver up to 525,000 megawatt-hours of heat a year starting in 2027. That will heat about 70,000 apartments.

The deal tests whether the AI boom’s biggest liabilities—its appetite for electricity and the heat its chips throw off—can become assets for a city that wants to stop burning things. It also tests whether going green can pay. Both companies are betting it can: OnZero gets a new revenue stream, and Helen gets heat it says costs less than burning wood or gas.

“The main idea is that one can solve all the criticisms and therefore problems of data centers by looking at a data center not as a consumer of electricity, but as an energy system asset that connects the electricity grid with the heat grid,” Ali Siddiqui, OnZero’s chief executive, told me in an interview. “The problem of water use, the problem of what to do with the heat, the problem of emissions profile, all of these go away.”

Most data centers treat that heat as trash. Servers turn almost all the electricity they draw into heat, and operators use more electricity on fans and chillers to blow it outdoors. Many large sites also run cooling towers that evaporate water: Google’s biggest U.S. data center, in Council Bluffs, Iowa, consumed 1.3 billion gallons of water in 2025, roughly 3.6 million gallons a day, the company reports.