Data Center Heat Reuse: Greenhouses, Desalination, and the Grade of Heat You Have

Data center heat reuse means capturing the thermal energy a facility rejects and delivering it to a real offtaker (a district heating network, a greenhouse, or a desalination process) instead of dumping it to the air. Nearly all the electricity a data center draws leaves as heat: a 1 MW IT load produces roughly 8,760 MWh of thermal energy a year. At European scale, the technical potential is about 221 TWh annually, roughly 12% of EU district-heating demand (European Data Centre Association, 2025). Whether that heat is usable depends almost entirely on one variable, the cooling method. Air cooling gives you low-grade 25–40°C heat; liquid and immersion cooling deliver 50–60°C and up, which modern heat networks and greenhouses can use directly.

This post covers how much heat is available, why cooling grade decides everything, the proven greenhouse and district-heating cases, where desalination actually stands, the EU rules forcing the issue, and why modular designs are heat-ready by default.

How much heat does a data center actually produce?

Almost all of it. The first law of thermodynamics doesn't negotiate, the electricity goes in, and it comes out as heat.

A 1 MW IT load running continuously produces about 8,760 MWh of thermal energy a year, and more once cooling and power-conversion overhead are counted: roughly 11,400 MWh at a PUE of 1.3 (Energy Solutions Intelligence, 2026). Scale that to a continent and the number gets serious. The European Data Centre Association estimates a theoretical potential of 221 TWh a year, about 12% of EU district-heating demand (EUDCA, 2025), a figure the World Economic Forum has since amplified (WEF, 2026).

Worth stating plainly: 221 TWh is a technical potential, not heat being delivered today. Most facilities still vent it. The reason isn't ignorance, it's that most of them can't produce heat anyone wants. Which brings us to the variable that matters. PUE is the efficiency metric underneath all of this; if it's unfamiliar, start with how to calculate and improve PUE.

Why does the type of cooling decide everything?

Because heat is only as useful as it is hot, and your cooling method sets the temperature at the door.

Sources: ScienceDirect review, 2025; MDPI Applied Sciences, 2026.

Air-cooled halls produce heat around 25–40°C. Modern district heating wants water above 70–80°C, so that low-grade heat has to be boosted with large heat pumps, which work, but consume electricity and lower net efficiency. That's an honest trade-off, not a dealbreaker. Meta's Odense facility does exactly this, upgrading sub-50°C waste heat with heat pumps before feeding the network (Meta, 2020).

Liquid and immersion cooling change the starting point. They deliver 50–60°C and higher, which can feed 4th- and 5th-generation heat networks with little or no upgrading. ASHRAE's warmer liquid-cooling water classes are specifically identified as district-heating candidates (ScienceDirect, 2025). Higher-grade heat is both more valuable and cheaper to reuse. This is the single biggest reason the cooling architecture decision, covered in modular data center cooling: free cooling vs DX vs hybrid and liquid cooling for data centers, also decides your heat-reuse options.

Are data centers really heating greenhouses today?

Yes, at demonstration scale, and greenhouses are the friendliest offtaker because they accept low-grade heat directly.

A greenhouse wants 25–40°C air. That's exactly what an air-cooled data center rejects, so no heat pump is needed. In Boden, Sweden, an energy company working with RISE and Luleå University built a data-center-heated greenhouse that holds around 25°C year-round even at −30°C outside (RISE, 2024). In Luleå, a project grows microgreens hydroponically on waste heat. In Lévis, Québec, QScale designed its flagship campus to route surplus heat to neighboring greenhouses (Data Centre Magazine, 2024).

The district-heating cases prove the model at scale. Meta Odense donates about 100,000 MWh a year to the local Fjernvarme Fyn network (Meta, 2020). Stockholm's Open District Heating program turned recovered data-center heat into a tradable product, with deals like DigiPlex warming around 10,000 households and heat sold under contracts worth roughly SEK 2 million per MW per year (Stockholm Exergi; Data Centre Solutions). That last number is the point: a cooling cost became a revenue line. The broader business case for treating rejected heat as an asset is laid out in data center waste heat recovery: turn cooling costs into revenue.

The binding constraint, as Stockholm and Odense both show, isn't the heat. It's having an offtaker and a network next to the building.

Can data center waste heat drive desalination?

It's promising, but early-stage, and it's worth being precise rather than optimistic here.

Thermal desalination methods like multi-effect distillation generally need feed heat around 70–75°C or higher, which is impractical for air-cooled facilities and marginal even for liquid-cooled ones (Lund University, 2024). So the headline thermal methods are mostly out of reach without significant temperature upgrading.

Membrane distillation is the realistic path. It separates saline water by moving vapor across a hydrophobic membrane rather than boiling, so it can run on low-grade waste heat (ScienceDirect, 2019). A Lund University techno-economic study modeling a 1.5 MW direct-to-chip data center in Barcelona found membrane distillation technically feasible but economically challenging at current costs (Lund University, 2024). A 2026 concept even pairs seawater evaporation with data-center cooling to produce freshwater directly, though that's at lab stage (ScienceDirect, 2026).

No commercial-scale data-center-coupled desalination plant is operating yet. Membrane distillation is the technology to watch precisely because it tolerates the low-grade heat most facilities have. Treat desalination as a credible R&D frontier, not a deployment you can order today.

What EU rules are forcing heat reuse?

Two instruments, and conflating them is the most common mistake, so keep them separate.

Germany's Energy Efficiency Act (EnEfG) is binding national law. New data centers must reuse a rising share of their energy: at least 10% from 1 July 2026, 15% from July 2027, and 20% from July 2028, for facilities with non-redundant connected load at or above 300 kW, roughly 1,000 German data centers (White & Case, 2024). Miss it and the fines run into the tens of thousands of euros per violation.

The EU Energy Efficiency Directive (the 2023 recast, Directive 2023/1791) is a framework transposed by member states. It's a different mechanism: facilities above 1 MW must use waste heat or demonstrate it's infeasible through a cost-benefit analysis, and facilities at or above 500 kW of installed IT power must report annually on sustainability KPIs including heat reused (European Commission; Covington, 2025). So EnEfG mandates a percentage; the EED requires reporting and a use-or-justify test. Don't present the EED as imposing a fixed reuse quota, it doesn't. The full regulatory map is in EU data center regulations 2026.

Why are modular data centers heat-ready by default?

Because the three things that make heat reuse work (high-grade heat, proximity to an offtaker, and pre-plumbed recovery) are design choices a factory can make once and repeat.

Liquid cooling by design means higher-grade heat. Modular units built around direct-to-chip or immersion cooling deliver 50–60°C-plus that can feed district heating or greenhouse loops with little or no heat-pump boost, versus the sub-40°C air-cooled heat that dominates legacy halls (MDPI, 2026). Siting flexibility means you can put the module next to the offtaker (a greenhouse cluster, an agri-park, or a coastal site suited to membrane-distillation research) instead of hoping a network happens to run past a fixed building. And heat-exchanger and coolant-distribution plumbing can be pre-engineered into the module, making a facility heat-ready from day one, which is exactly what the WEF recommends: build heat-ready even before a network exists (WEF, 2026).

Put those together with the regulatory tailwind and the calculus flips. EnEfG's rising thresholds and the EED's use-or-justify test turn heat recovery from a compliance burden into a design default and, on the Stockholm model, a revenue stream. Most operators still treat waste heat as a disposal problem. The ones sizing liquid-cooled, heat-ready capacity now are the ones who'll be selling megawatt-hours in 2028 instead of filing infeasibility reports. The broader sustainability picture is in green data centers: design, certification, and real-world examples, and the full delivery model in the definitive guide to modular data centers.

Frequently asked questions

How much heat does a data center actually produce? Almost all the electricity a data center draws is converted to heat. A 1 MW IT load running around the clock yields roughly 8,760 MWh of heat a year, and about 11,400 MWh once cooling overhead is included at a PUE of 1.3 (Energy Solutions Intelligence, 2026).

How much of Europe's heating could data-center waste heat cover? The European Data Centre Association estimates a theoretical potential of 221 TWh a year, roughly 12% of EU district-heating demand (EUDCA, 2025, cited by WEF, 2026). It is a technical-potential figure, not heat being delivered today.

Why does the type of cooling matter so much for heat reuse? Air cooling produces low-grade heat around 25–40°C, which usually needs a heat pump to be useful, while liquid and immersion cooling deliver 50–60°C or higher that can feed modern district heating or greenhouse loops directly (ScienceDirect, 2025; MDPI, 2026). Higher-grade heat is more valuable and cheaper to reuse.

Are data centers really heating greenhouses today? Yes, at demonstration scale. In Boden, Sweden, a data-center-heated greenhouse stays around 25°C year-round even at −30°C outside (RISE, 2024), and QScale's Lévis campus in Québec is designed to feed neighboring greenhouses (Data Centre Magazine, 2024). Greenhouses are attractive because they accept low-grade heat directly, without a heat pump.

Can data center waste heat be used for desalination? It's promising but early-stage. Thermal methods like multi-effect distillation typically need 70–75°C, impractical for most data centers, whereas membrane distillation can run on low-grade heat; a Lund University study of a 1.5 MW site in Barcelona found it technically feasible but not yet economical (Lund University, 2024). No commercial-scale plant is operating yet.

What EU rules push heat reuse? Germany's Energy Efficiency Act (EnEfG) requires new data centers to reuse at least 10% of their energy from July 2026, rising to 15% in 2027 and 20% in 2028 (White & Case, 2024). The EU Energy Efficiency Directive is a separate framework requiring large data centers above 1 MW to use waste heat or prove it infeasible, plus annual reporting for facilities at or above 500 kW (European Commission; Covington, 2025).

Why are modular data centers well-suited to heat reuse? Modular units built around liquid cooling deliver higher-grade 50–60°C-plus heat usable with little or no upgrading, can be sited directly next to a greenhouse or heat network, and can have heat-recovery plumbing pre-integrated at the factory (MDPI, 2026). That makes a facility heat-ready from day one, turning EnEfG and EED obligations into a design default rather than a retrofit scramble.