Data centers are famous for what they consume: electricity and cooling. Less famous is what they produce every second they’re online: heat.
In certain parts of Northern Europe, that “problem” is already being piped into district-heating networks and delivered to apartments as steady, low-carbon warmth.
The heat hiding in the cloud
Online platforms don’t feel physical, but they run on very physical infrastructure. A brand like Royal Vegas Casino, for example, isn’t just a website with a few games behind it.
It’s a high-availability digital service that has to stay responsive 24/7, handle payments securely, protect user accounts, log activity for compliance, and keep gameplay smooth across devices.
Add real-time promotions, personalization, and customer support tools—and the back-end workload grows quickly.
Storing data for a website like that is quite intensive, but needed as well. That’s how they can recommend to their users new products they might like according to their necessities and taste. However, it generates heat inside the building.
The International Energy Agency notes that nearly all data-center electricity becomes usable heat, but around 70/80% can be recovered at scale with heat pumps when the site is close enough to a district-heating network.
AI makes that prize even bigger; the IEA says data centers currently account for about 1.5% of global electricity demand and that demand is set to double by 2030.
Helsinki: turning server rooms into radiators
Helsinki’s utility, Helen, treats data centers like steady heat producers. Operators are capturing waste heat and sending it to Helen’s system, where industrial heat pumps lift it to district-heating temperatures. Helen says one data center can heat up to 20,000 apartments in the city.
Telia’s data center, for example, can recover up to 90% of its waste heat, enough for about 14,000 two-room apartments today, with an expected rise to roughly 28,000 as capacity expands.
The technical logic is straightforward. Servers run 24/7 and must be cooled continuously, instead of dumping warm air (or warm water in liquid-cooled halls) outdoors, a heat exchanger transfers it to a secondary loop.
Large heat pumps then “upgrade” that low-grade heat to about 85ºC so it can circulate through the city’s hot-water pipes, exactly the range a mature district-heating grid expects.
Espoo: a data-center cluster as baseload heating
Helsinki is not the only Finnish city trying this idea. In the very same region, Fortum and Microsoft are connecting new data centers in Espoo and Kirkkonummi to the district-heating network.
Fortum says the sites will eventually provide around 40% of the area’s district heat, and that roughly 75% of the data centers’ waste heat will be used annually for district heating, with the summer demand as the limiting factor.
Reuters has reported that Microsoft’s newer “power first” approach (building where abundant, emission-free electricity exists) makes the Nordics attractive, and that the company is partnering with local heat producers to redistribute waste heat to homes.
Why it works—and what can block it?
The Nordics have three big advantages: dense district-heating networks, cold climates that keep heating demand high, and deep experience with industrial heat pumps. But the model has important constraints that might make it too difficult to work as it should, in theory.
You need proximity, clear contracts for buying and selling heat, and a plan for summer when buildings need less. And while heat recovery improves overall efficiency, it doesn’t shrink the data center’s electricity appetite: so decarbonising the grid remains non-negotiable.
A near-term climate win hiding in plain sight
If more cities connect these dots, the upside is sizeable. The IEA estimates that, within 5 km of district-heating networks, reused data-center heat could provide up to 300 TWh of space heating in Europe by 2030—enough for around 10% of European homes.
The servers will keep humming either way; the real question is whether we keep dumping their heat into the sky, or treat it like the urban energy resource it already is.
