Data centre waste heat reuse depends on who is next door

Key takeaways

• Few EU data centres reuse heat today. Of 770 sites in the first reporting round in 2024, 67 reported any reuse. About 1.8% of all the heat they produced was reused, according to the Commission’s report COM(2026) 500, which warns that the data are partial.
• Under section 11 of Germany’s Energy Efficiency Act (EnEfG) as in force, a site that starts operating from 1 July 2026 must reach a 10% energy reuse share within two years. Later start dates face a planned share of 15% or 20%. Two of the three exemptions depend on a municipality or a heat-network operator.
• The amendment bill, Bundestag document 21/8027, would allow four years and add an exemption where no reasonable heat-network connection exists. It is still a bill. Its own memorandum says the sites chosen for large AI data centres often lack a suitable heat network.
• For a hall with 1 MW of IT load at a PUE of 1.2, a 10% share is 1,051 MWh of heat a year, or 120 kW on average. That is 12% of the heat the IT equipment gives off (our calculation).
• Heat arrives years after the servers. Microsoft’s waste heat in Espoo was announced in March 2022 (City of Espoo) and is due from 2027, per Fortum. atNorth’s site near Copenhagen became operational in the first quarter of 2026, while heat delivery is expected from 2028, per its June 2026 sustainability report.

In the first EU reporting round in 2024, 770 data centres sent in their figures. Only 67 reported reusing any of their waste heat. Across the group, about 1.8% of the heat produced was put to use, according to the European Commission’s report COM(2026) 500 of 21 September 2026. The Commission adds cautions: the 770 sites were about 36% of those required to report, some Member States with known heat projects reported none, and some computed values were unrealistically high.

Regulators now ask for more. Germany requires sites starting from 1 July 2026 to reuse at least 10% of their energy (a planned 15% or 20% for later start dates), and France treats a site as compliant at 20%. Capturing the heat is a known engineering task. Selling it depends on what lies outside the fence: a network nearby with room in it, and a buyer in July. The German government’s memorandum to its own amendment bill says so about the sites chosen for large AI data centres: “An den entsprechenden Standorten fehlt es zudem häufig an einem geeigneten Wärmenetz, in das die Abwärme eingespeist werden kann” (at those sites there is also often no suitable heat network into which the waste heat can be fed; our translation of Drucksache 21/8027, p. 64).

What follows is a reading of the texts for planning, not legal advice. The status of each rule is in our regulation tracker, and the debate on the German bill is in our hearing report.

What the rules ask for

Germany has the most specific numbers. Section 11(2) of the EnEfG, as in force, requires a data centre that starts operating from 1 July 2026 to reach an energy reuse share of at least 10%, calculated under the standard DIN EN 50600-4-6. For later start dates the text asks for a “geplanten Anteil”, a planned share: 15% from 1 July 2027 and 20% from 1 July 2028. The section does not define what “planned” adds. The share must be met as an annual average within two years of start-up. A breach can be fined up to EUR 100,000 (section 19).

Section 11(3) releases an operator in three cases. One covers events outside its control. The second is an agreement in which a nearby municipality or heat-network operator declares its intent to build or permit networks with which the target can be met within ten years. The agreement must include an investment plan, who pays for the connection line, and the heat price. The third applies when a nearby network operator does not accept an offer of the heat at generation cost within six months. It requires the data centre to have the necessary infrastructure, in particular a heat transfer station, which is the exchanger where heat passes to the network. Two of the three routes turn on someone else’s decision.

The government’s amendment bill would change these terms. It had its first reading on 24 September 2026 and a committee hearing on 5 October. Until it passes and is promulgated, the stricter text in force applies.

Point	EnEfG section 11, in force	Bill 21/8027 (proposal, not law)
Reuse share for new sites	10% for start from 1 Jul 2026; planned 15% from 1 Jul 2027; planned 20% from 1 Jul 2028	Same levels
Time to reach the share	At most two years after start-up, as an annual average	At most four years after start-up
Heat used on site (own offices and operating rooms)	No provision in section 11	Counts towards the share
Falling below the share	Only through the exemptions	Allowed if the site is connected to a heat network
Exemption 2: agreement with municipality or network operator on networks that meet the target within ten years	Needs an investment plan, a connection-cost rule and the heat price	Investment-plan and cost conditions not in the text
Exemption 3: refused offer at generation cost, six months	Operator must hold the infrastructure, in particular a heat transfer station	Station condition dropped; space for heat infrastructure must be kept free
Exemption 4: no reasonable connection	Does not exist	No technically and economically reasonable connection to an existing or planned heat network, shown by a cost-benefit analysis
Which sites count as data centres	From 300 kW non-redundant electrical connection power	From 500 kW installed IT power

The memorandum gives the reason for the new exemption: new AI data centres need sites with enough grid connection, and those sites often lack a suitable heat network. A connected site may fall below the share, it adds, because the network may lack the capacity to take the minimum amount.

At EU level, Article 26(6) of the Energy Efficiency Directive (EU) 2023/1791 requires Member States to ensure that data centres with a total rated energy input above 1 MW “utilise the waste heat or other waste heat recovery applications unless they can show that it is not technically or economically feasible”. Feasibility is tested by a cost-benefit analysis. Under Article 26(7) it must cover “local heat demand, including seasonal variation” and the connection to a district heating network. Article 26(8) lets Member States exempt sites whose heat goes to such a network from the cost-benefit analysis, and set thresholds such as the distance to one.

France has written a number into its rules. Decree 2025-1382, in force since 1 January 2026, deems a site to recover its waste heat at an energy reuse factor of at least 0.20. A ministerial order may raise that to 0.40. A cost-benefit analysis can justify less. Sites whose permit application predates 2026, and that do not recover heat, must send that analysis by 1 October 2027.

What the reuse factor counts

All these shares are an energy reuse factor (ERF). Annex III of Delegated Regulation (EU) 2024/1364 defines it as ERF = E_REUSE / E_DC. E_REUSE is the waste heat reused, in kWh. E_DC is the total energy the data centre takes in, cooling energy included. A 10% ERF is therefore 10% of total energy, which is more than 10% of the IT load.

Annex II sets the counting rules. Reused energy is measured at the boundary, where the heat is handed to the other party, and only heat reused outside the data centre counts. The ratio is blind to temperature. The Commission’s technical study notes that ERF “may not differentiate between the different types of heat produced”. A kWh at 28 °C counts the same as a kWh at 80 °C. The annual reporting duty is covered in our EED reporting guide.

One point is open. If the heat pump sits inside your boundary, the heat measured at the handover includes the compressor’s work. Whether the pump’s electricity must then enter E_DC is for the measurement standard to settle, and we have not read it. EnEfG section 11(2) leaves such electricity out of the PUE test (PUE, power usage effectiveness, is total energy divided by IT energy) but says nothing about the ERF. Agree the boundary with your auditor before you size the plant.

Why 28 °C heat is hard to sell

An air-cooled hall keeps server inlets cool, so the heat it rejects is lukewarm. AWS says its data centre in Tallaght, Dublin, warms the water running through the building to about 23 to 28 °C (AWS, March 2024). At Telia’s Helsinki data centre, heat pumps built by Helen take cooling water at about 30 °C and send it back at about 20 °C (Telia, February 2024).

Heat networks run hotter. Four of the six projects below state supply temperatures of 70 to 85 °C, and older Scandinavian networks work at around 90 °C (Boesten et al., 2019). The 2014 paper that defined fourth-generation district heating, by Lund and colleagues, suggests that future networks may use 50 °C in the supply pipe and 20 °C in the return (Energy 68).

A heat pump closes the gap. It uses electricity to move heat from a cool source to a warmer sink. Its coefficient of performance (COP) is the heat delivered per unit of electricity. Physics caps it at the Carnot limit, COP = T_hot / (T_hot − T_cold), with temperatures in kelvin (degrees Celsius plus 273.15). The smaller the lift, the higher the limit.

Take 28 °C hall water lifted to a 70 °C network. The lift is 42 K, and the Carnot limit is 343.15 / 42 = 8.17 (our calculation). Real machines reach a fraction of that. A 2017 Heat Roadmap Europe survey of large heat pumps in district heating, by David and colleagues (Energies 10, 578), found an average practical COP of 3 to 4 over a year, excluding electricity for auxiliary source pumps. Its best was 6.5, for two Swedish units that raise the district-heating return by a few degrees; an ammonia unit boosting about 30 K reached 6.3. Its worst was 2.65, for a 75 K difference. In the authors’ words, “the smaller the temperature increase is, the higher the COP”.

For planning we take 45% of the Carnot limit, which gives a COP of 3.7 for the 42 K case, inside the survey’s 3 to 4. Where that rule gives more than 6, we cap it at 6.

Source to sink	Lift	Carnot limit	Planning COP	Electricity per MWh of heat
28 °C to 55 °C (low-temperature network)	27 K	12.15	5.5	0.18 MWh
28 °C to 70 °C	42 K	8.17	3.7	0.27 MWh
28 °C to 85 °C (top of the Tallaght and Helsinki supply ranges)	57 K	6.28	2.8	0.36 MWh
50 °C to 70 °C (liquid loop, assumed)	20 K	17.16	6.0 (capped)	0.17 MWh

What liquid cooling changes

Liquid cooling raises the source temperature. Cold plates or immersion carry heat from the chips into a fluid that can run warmer than hall air. A warmer source means a smaller lift. In the table, moving the source from 28 °C to 50 °C for the same 70 °C network takes the planning COP from 3.7 to 6. That cuts the electricity per MWh of heat by 38% (our calculation). Our liquid cooling explainer covers the hardware.

The 50 °C is our assumption for illustration. We found no primary source for a typical return temperature in current liquid-cooled halls, so use your own design value.

Liquid does not take all the heat. In a 2014 test of a cold-plate retrofit by Lawrence Berkeley National Laboratory (LBNL-6641E), the best results were 67 to 75% of server power captured with supply water at 15 to 20 °C, and 57 to 59% at 30 °C at 50 to 100% load (35% at idle). The captured share fell as the return temperature rose. That product predates current GPU cold plates, so read the numbers as a direction. The rest of the heat still leaves through the air, at low temperature.

The EED already points this way. Article 26(7) tells the cost-benefit analysis to “consider cooling system solutions that allow removing or capturing the waste heat at useful temperature level with minimal ancillary energy inputs”. atNorth’s DEN01 site in Ballerup, near Copenhagen, follows that route: its November 2025 release says the warm water comes from direct liquid cooling. It gives no temperature.

What 10% reuse means for a 1 MW hall

Take a hall with 1 MW of IT load running all year at a PUE of 1.2, the limit EnEfG sets for new sites. The inputs are below, then the results. Every derived figure is our calculation.

Input	Value	Basis
IT load	1.0 MW, constant, 8,760 hours a year = 8,760 MWh	Assumption
PUE	1.2	EnEfG section 11(2) limit for new sites
Total energy, EDC	8,760 × 1.2 = 10,512 MWh a year	Heat-pump electricity kept outside EDC (assumption, see the open point above)
Air-cooled hall water	28 °C	Within 23 to 30 °C (AWS, Telia)
Liquid loop water	50 °C	Assumption for illustration
Network supply	70 °C	Odense 70 to 75 °C (Ramboll); Tallaght 70 to 85 °C (AWS)
COP	3.7 air; 6.0 liquid	45% of Carnot, capped at 6 (table above)
Heat per home	17.9 MWh a year	Odense: 215,000 MWh / 12,000 homes (Ramboll)

Reuse share (ERF)	Heat delivered	Average heat flow	Share of IT heat	Homes at the Odense ratio	Heat-pump electricity, air (COP 3.7)	Heat-pump electricity, liquid (COP 6)
10% (EnEfG, start from 1 Jul 2026)	1,051 MWh/yr	120 kW	12.0%	59	284 MWh/yr	175 MWh/yr
15% (EnEfG planned share, from 1 Jul 2027)	1,577 MWh/yr	180 kW	18.0%	88	426 MWh/yr	263 MWh/yr
20% (EnEfG planned share from 1 Jul 2028; France 0.20)	2,102 MWh/yr	240 kW	24.0%	117	568 MWh/yr	350 MWh/yr

The volume is small. A 10% share is 120 kW on average, while the hall gives off about 1 MW of heat all year. At the ratio in Meta’s Odense project, 1,051 MWh is the heat for about 59 homes. At 20% it is about 117. In this assumed case the target uses a fraction of the heat available, but the calculation does not establish that capture or delivery is straightforward at a particular site.

The average hides the season. German law asks for the share as an annual average. A network that takes little heat in summer must take more than 120 kW in winter for the year to add up. Fortum expects to use about 75% of the Espoo data centres’ waste heat over a year, because “the need for heating is very low in the summer months” (Fortum).

The electricity is modest. At COP 3.7 the 10% case needs 284 MWh of compressor electricity a year, about 2.7% of the site’s 10,512 MWh. At COP 6 it needs 175 MWh. If the heat pump sits inside the boundary, the hall gives up only 767 MWh of the 1,051 MWh handed over at COP 3.7; the compressor supplies the rest. The price of that electricity against the price of heat is what the network operator will negotiate.

What the surroundings decide

A network has to exist, with room in it. The Commission’s technical study assumes that the largest sites, above 10 MW, reuse only small parts of their heat. Its authors suggest that “there often are not many local offtakers which can take such enormous amounts of heat constantly” (p. 42). A Heat Roadmap Europe mapping report from 2016 calls district heating “almost impossible” below 30 TJ of heat demand per km² (8.3 GWh, our conversion). Our siting guide has no heat-network map yet; for a new site it is a layer to add.

Someone has to pay for the pipe. Ireland’s National Heat Study for the energy agency SEAI estimates installed inner-city two-pipe plastic district-heating pipework at EUR 782 per metre for 50 mm pipe and EUR 869 for 125 mm, in 2020 prices (SEAI, appendix B). Cost rises slowly with diameter, the study notes, which the study takes to suggest length is the main driver. At those rates 1 km costs EUR 0.78 million to 0.87 million (our calculation). Westville in Frankfurt planned a 500 m pipe, according to trade magazine Haufe (2021). Fortum’s Espoo programme includes about 15 km of main pipeline within a EUR 225 million investment for 2023 to 2027 that also pays for heat plants (Fortum, June 2023). Fortum’s May 2026 release adds a thermal storage facility and puts investment in the heat pump plants at about EUR 225 million.

Demand has a season, while data-centre heat is flat all year. COM(2026) 500 says that “even in regions with high heating demand, the seasonality of demand remains a major barrier for high heat reuse rates”. It concludes that “it is difficult to set a target for ERF”, which bears on the EU minimum performance standards now under consultation. For the latest EU figures, see our reading of the 2025 dashboard.

Municipal heat plans show where networks may come. Germany’s Heat Planning Act (WPG) requires them by 30 June 2026 in municipalities above 100,000 residents and by 30 June 2028 elsewhere (section 4). A plan gives you nothing to enforce: section 23(4) says it “begründet keine einklagbaren Rechte oder Pflichten”, no enforceable rights or duties. Network operators do face pressure. From 2030 each heat network must, with exceptions and extensions possible to 2034, draw at least 30% of its net heat from renewables or unavoidable waste heat, and 80% from 2040 (section 29). We have not confirmed that data-centre heat qualifies; if it does, network operators have a reason to want it.

Contracts decide who carries the cost. Helen in Helsinki offers two models (Helen). Either Helen invests in heat recovery and takes the heat in return for the cooling it provides, or the data centre invests and Helen buys heat that meets network requirements. In Germany, EnEfG section 17 obliges a company with waste heat to tell a network operator who asks its annual heat quantity, maximum thermal power, availability over the year and temperature. The figures also go to a public waste-heat platform, so networks can find you first.

Six European projects, as their sources state them

The figures below are what each source says, and they are not comparable measurements. Five of the six name heat pumps; atNorth’s release does not say.

Project	Heat partner	What the source states	Temperatures	Dates and status	Source
Meta, Odense, Denmark	Fjernvarme Fyn	Heat production about 45 MW; expected recovery 215,000 MWh; more than 12,000 homes (2023)	Heat pumps raise heat to 70 to 75 °C	Ready for operation late 2019	Ramboll, owner’s engineer (page undated)
Microsoft, Espoo, Kauniainen and Kirkkonummi, Finland	Fortum	72 water-to-water heat pumps, up to 180 MW of district heat; data-centre heat to cover about 40% of 2 TWh yearly demand at full implementation; about 75% of the waste heat used over a year	Not stated	Announced 17 Mar 2022; heat plants started May 2026 on outdoor air and electric boilers; data-centre heat in phases from 2027	Fortum, May 2026; City of Espoo, 2022
AWS, Tallaght, Dublin, Ireland	Heatworks network, South Dublin County Council	3 MW of heat (AWS); 4.88 GWh a year produced, 4.33 GWh sold, 6 customers, 3.8 km of network (factsheet)	23 to 28 °C from the data centre; first stage to about 45 °C, second to 70 to 85 °C; design 70/50 °C	Network opened 6 Apr 2023	AWS; SDCC; ENABLE DHC factsheet
Telia, Pitäjänmäki, Helsinki, Finland	Helen	About 60% of heat reused after a few months, goal about 80% (Telia, Feb 2024); up to 14,000 two-room apartments eventually, plan for 28,000 (Helen, May 2025)	In about 30 °C; out 80 to 85 °C; return about 20 °C	Heat recovery commissioned spring 2023	Telia; Helen
atNorth DEN01, Ballerup, Denmark	Vestforbrænding	22.5 MW site; heat from direct liquid cooling for over 8,000 homes	Not stated	Site operational Q1 2026; heat expected from 2028	atNorth release, 26 Nov 2025; atNorth sustainability report, June 2026
Telehouse, Westville, Frankfurt, Germany	Mainova	At least 2,400 MWh a year of data-centre heat for about 1,300 apartments, plus 1,600 MWh of Mainova district heat; two 320 kW heat pumps; 500 m pipe; 15-year contract	Lifted to about 70 °C	First delivery planned 2023, completion planned 2025; current status not confirmed	Haufe (trade press, project data); ZfK, operator name

Capacity is larger than delivered heat. Tallaght’s 4.88 GWh a year from 3 MW is a capacity factor of 18.6%. Odense’s 215,000 MWh from about 45 MW is 55%, if the figure is yearly, which the page implies (our calculations). Announced heat dates are two to three years after the Ballerup agreement (Nov 2025 to 2028) and five years after the Espoo announcement (Mar 2022 to 2027); neither has been delivered yet. Westville is closest in scale to the worked case: 2,400 MWh a year is a little above the 20% case for a 1 MW hall.

Questions to settle before you sign a heat contract

1. Which network is in reach, and does it have spare capacity all year? Ask in writing, and read the municipal heat plan for networks still to come.
2. What supply temperature does the network need in winter and in summer? That sets the lift and the heat pump’s electricity.
3. What water temperature will your hall really hand over? Measure it in operation, and check whether liquid-cooled rows can run warmer.
4. Where is the ERF boundary? Agree where reused heat is metered, and on which side of the meter the heat pump sits.
5. Who owns and runs the heat pump, who pays for the connection line, and how do electricity price changes pass into the heat price?
6. How much heat will the network take in July? Ask about storage and where the surplus goes.
7. What is the fallback if no network is in reach? Keep the EU cost-benefit analysis on file. In Germany, document the agreement or the refused offer that section 11(3) recognises.

Espoo shows the order of events. Fortum’s new heat plants started in May 2026 on outdoor air and electric boilers. The first Microsoft waste heat is due in phases from 2027, five years after the March 2022 announcement (City of Espoo; Fortum). Under the law in force, a German site that started on 1 July 2026 has until 1 July 2028 to show its 10%.

Sources

• European Commission, COM(2026) 500, 21 September 2026 (Council copy); EUR-Lex
• European Commission technical study, doi 10.2833/3168794
• EnEfG section 11; EnEfG full text
• Bundestag Drucksache 21/8027
• Directive (EU) 2023/1791, Articles 12 and 26
• Delegated Regulation (EU) 2024/1364, Annexes II and III
• Décret n° 2025-1382 du 29 décembre 2025
• WPG section 4; section 23; section 29
• Lund et al., Energy 68 (2014)
• Boesten et al., Adv. Geosci. 49 (2019)
• David et al., Energies 10, 578 (2017)
• LBNL-6641E (2014)
• STRATEGO WP2 background report 6
• SEAI National Heat Study, appendix B
• Fortum, June 2023; Fortum, May 2026; Fortum, Helsinki region data centres
• City of Espoo, 17 March 2022
• Ramboll, Meta Odense project page
• AWS, March 2024; South Dublin County Council, 6 April 2023; ENABLE DHC Tallaght factsheet
• Telia, 6 February 2024; Helen, 26 May 2025; Helen heat recovery service
• atNorth via PR Newswire, 26 November 2025
• Haufe, Westville project report

@online{scienceshot-data-centre-waste-heat-2026,
  author       = {Turner, Alex},
  title        = {{Data centre waste heat reuse depends on who is next door}},
  organization = {ScienceShot},
  date         = {2026-10-16},
  year         = {2026},
  url          = {https://scienceshot.com/post/data-centre-waste-heat-reuse-europe}
}