Almost all the electricity a data center pulls off the grid comes back out as heat. One overview of the field puts the figure at roughly 90%. A data center is, in effect, a very expensive radiator. But most of that warmth goes nowhere useful. It gets blown into the sky.

The interesting question is what a facility could do with the heat if it decided not to throw it away. Meta’s site in Odense, Denmark is one of the few places we can point to for an answer.

Where the wasted heat goes

Cooling is where the energy disappears. The Environmental and Energy Study Institute estimates that about 40% of the energy a data center uses goes to keeping the servers cool, and nearly all of that ends up as heat.

The catch is temperature. Server exhaust comes off warm but not hot, and warm-but-not-hot isn’t much good to anyone who wants to heat a building. The low temperature of that waste heat limits its direct use, so it has to be raised before it can heat homes. Which is where Odense gets clever.

What Odense actually does

The method is less exotic than it sounds. Water from the city’s district-heating network is run through the data center’s cooling units, where it picks up the low warmth coming off the servers. It then travels to a nearby plant full of heat pumps, which lift the temperature the rest of the way before the water goes out to homes.

The engineering consultancy Ramboll, which designed the recovery system for the district-heating company Fjernvarme Fyn, says the ammonia heat pumps raise the water to 70 to 75°C, hot enough for radiators, before it enters the network.

Meta’s own energy specialist, Lauren Edelman, frames the innovation as one of scale rather than parts. Edelman says, “Heat pumps are not a new invention, nor are coils for capturing heat. What is new and innovative is the pairing of these two in hyper scale.” Nothing here is new physics. The parts are ordinary. Doing it at the size of a hyperscale data center is the unusual bit, though that assessment does come from the operator.

The output isn’t small. Ramboll’s project scope describes about 45 MW of heat going directly into the Odense network, and the plant is the largest heat-pump installation in Denmark.

Why the home count keeps changing

Ramboll’s figures describe recovering 215,000 MWh a year and heating more than 12,000 homes. Go looking, though, and you’ll find smaller numbers attached to the same project. The numbers track the project’s phases and who is counting.

Meta’s early materials cite roughly 6,900 homes and 100,000 MWh a year for the first infrastructure. After an expansion, Meta’s own figure rose to 165,000 MWh and 11,000 homes. Ramboll’s 2023 figure put the full system at more than 12,000 homes, but Fjernvarme Fyn said in 2025 that Meta’s data centre was in practice supplying surplus heat equivalent to about 11,000 households.

Different scopes, different years, different counters. The range reflects how these projects grow.

Can anyone else copy it?

The heat pumps and coils are available to anyone. What Odense has that most places don’t is somewhere for the heat to go.

Jan Strømvig, who runs Fjernvarme Fyn, is candid about that. He puts it this way: “Our project is relatively unique because we have a very large distribution network. And Facebook [now Meta] has placed the data centre completely inside our distribution network, so we can utilise the energy very, very efficiently in our system.” The underlying point holds regardless of source. The data center was dropped inside a heating grid that already reached thousands of homes.

Denmark’s setup makes the economics work in a way that’s hard to reproduce elsewhere. Widespread district heating is the rare ingredient, and heat doesn’t travel well, so you can’t site a data center far from the buildings it warms.

Momentum may be building anyway. Ramboll cites a Danish Data Centre Industry figure that 63% of data centers plan to use their surplus heat in the near futuren.

What Odense really demonstrates isn’t a piece of technology. The hard part was never the heat pump. It was having a pipe network already in the ground, wide enough to take everything a hyperscale data center can give.