When Data Centre Waste Heat Can Actually Be Used
Data centre heat reuse is not decided by a headline temperature alone. The source, the receiving network, year-round demand and the contract all matter. The European Commission's September 2026 report estimates that roughly 1.8% of heat generated by reporting EU data centres was reused, but warns that incomplete and imperfect reporting limits that estimate. This report separates that observation from legal targets and shows a reproducible temperature screening calculation.
What the EU's new 1.8% figure measures
Source: European Commission — COM(2026) 500 final: energy efficiency of data centres in the EU (2026)
The Commission reported on 21 September 2026 that approximately 1.8% of total heat generated was reused in the first EU reporting period; only 67 data centres reported any reuse. Its report also says the database was incomplete and contained questionable values, so this is not a definitive rate for every EU data centre. The percentage is a heat-reuse observation, not an average Energy Reuse Factor (ERF). It must not be compared directly with Germany's 10%, 15% and 20% requirements for cohorts of new data centres: the populations, periods and denominators differ.
The two European thresholds do different things
Source: EUR-Lex — Directive (EU) 2023/1791, Articles 12 and 26 (2023)
The recast Energy Efficiency Directive sets two separate duties, and they are often confused.
Article 12 applies to data centres with installed information technology power demand of 500 kilowatts or more. It is a transparency duty: publish the information listed in Annex VII and report it to the European database. It says nothing about where the heat must go.
Article 26 applies to data centres with a total rated energy input above 1 megawatt, which is a different quantity from installed IT power. It requires the operator to use the waste heat, or to apply other waste heat recovery measures, unless a cost-benefit analysis shows that this is not technically or economically feasible. A district heating connection is one way to satisfy it. Supplying an adjacent building, a greenhouse or a process load are others.
What temperature is available, and what each network wants
| Source or network | Typical temperature | Note |
|---|---|---|
| Air-cooled hall, heat rejected | 25–35 °C | Low grade, large and steady quantity |
| Direct-to-chip liquid cooling | 50–60 °C | Grade rises with coolant temperature |
| Third-generation network, illustrative supply | 80–100 °C | Existing systems vary; check the actual network |
| Fourth-generation network, illustrative supply | 50–60 °C | Supply and return temperatures vary by system and season |
| Fifth-generation network, ambient loop | −5 to 20 °C in one German survey | Survey of 53 networks, not a universal design range |
The pairing decides the engineering. A warm source can feed a cooler ambient loop through a heat exchanger if the available temperature difference exceeds the required exchanger approach. Connected buildings may still need their own heat pumps. A high-temperature network can instead require a central heat pump. Neither configuration is guaranteed by a generic cooling label.
Liquid cooling can provide a warmer source, but its usable temperature depends on the actual coolant outlet and the heat-exchanger design. For example, a 58 °C source and 55 °C network supply have a 3 K difference: that may work with an exchanger designed for a sufficiently small approach, but not with the illustrative 5 K approach used below.
Three reproducible temperature-screening cases
| Case | Source | Network supply | Assumed exchanger approach | Minimum source-side lift |
|---|---|---|---|---|
| A | Air-cooled, 30 °C | Ambient loop, 20 °C | 5 K | 0 K |
| B | Direct-to-chip, 55 °C | Fourth-gen, 60 °C | 5 K | 10 K |
| C | Air-cooled, 30 °C | Third-gen, 90 °C | 5 K | 65 K |
These are temperature-feasibility screens, not project economics or promised heat recovery. The minimum source-side lift in kelvin is max(0, network supply temperature in °C + assumed heat-exchanger approach in K − available source temperature in °C). For case A: max(0, 20 + 5 − 30) = 0 K. For case B: max(0, 60 + 5 − 55) = 10 K. For case C: max(0, 90 + 5 − 30) = 65 K. These inputs are chosen from indicative literature ranges; they are not observations from a single site. A zero result means no source-side temperature lift in this screen, not no pump electricity, no pipe cost, or a viable annual offtake.
ERF is an annual energy ratio, not a temperature score
Source: EUR-Lex — Delegated Regulation (EU) 2024/1364, Annex III (2024)
Under the EU reporting method, Energy Reuse Factor (ERF) = energy reused / total data centre energy. The metering boundary and measurement standard matter. As a purely illustrative arithmetic example, if a data centre uses 10,000 MWh of energy in a year and delivers 1,000 MWh of qualifying reused energy, ERF is 0.10 (10%). Delivering 1,500 or 2,000 MWh against the same denominator gives 15% or 20%. This is not a projection for any particular site and does not determine whether a specific German-law exemption applies.
Seasonal demand decides the value, not the peak
Data centres commonly produce heat throughout the year, but their load and availability vary. Space-heating demand is usually lower in summer, while domestic hot water, pools, greenhouses or industrial processes can provide different demand profiles. None is automatically available near the site. An hourly match between recoverable heat and contracted demand, including summer and maintenance periods, is needed to estimate annual delivered energy. A winter peak alone will overstate the result.
Where this screening calculation fails
The three cases do not estimate recoverable MWh, ERF, carbon savings, heat-pump coefficient of performance or payback. They assume a single source temperature, a single network supply temperature and a 5 K exchanger approach. Real systems change with load, season and return temperature. Some reject heat at more than one temperature; a network may accept heat at its return rather than supply line. Pipe distance, pumping, exchanger fouling, downtime, metering rules and the buyer's hourly demand can overturn a favourable temperature screen. For an investment decision, obtain measured temperature and flow profiles, a network specification, an hourly offtake curve, a priced connection design and a boundary-consistent energy balance.
What German law adds on top, and the clause worth reading
Section 11 of Germany's Energy Efficiency Act sets a PUE ceiling of 1.2 and a reused-energy share of at least 10% for data centres starting operation from 1 July 2026. The planned share is at least 15% for those starting from 1 July 2027 and 20% from 1 July 2028. The requirements are to be achieved on an annual-average basis no later than two years after commissioning. The reused-energy share refers to DIN EN 50600-4-6, November 2020 edition. Older German data centres are subject to different PUE deadlines; this is not a blanket rule for all facilities.
For the statutory PUE calculation, electricity used by plant exclusively upgrading the data centre's waste heat is excluded. This is a specific accounting treatment, not a declaration that heat-pump electricity is free or irrelevant to project economics. Capital cost, electricity cost, network heat price and emissions still matter.
Section 11(3) contains conditional exceptions to the reuse-share requirement. One requires a qualifying agreement with a nearby municipality or heat-network operator that includes an investment plan, connection-line cost allocation and a heat price, with the target achievable within ten years. Another concerns a nearby heat network that does not accept a cost-price offer within six months, provided the data centre has the necessary heat-delivery infrastructure ready, particularly a transfer station. Read the current statutory text and obtain site-specific legal advice before treating either route as an exemption.
Download the illustrative case inputs and formula (CSV). Values are a transparent temperature screen, not site measurements.
FAQ
What temperature is data centre waste heat?
Illustrative literature ranges are about 25–35 °C for air-cooled hall heat rejection and 50–60 °C for some direct-to-chip liquid cooling designs. Actual temperatures depend on the cooling system and operating conditions.
Does an air-cooled data centre always need a heat pump to reuse heat?
No. A sufficiently cool ambient loop may accept heat through an exchanger without a heat pump at the data centre, although connected buildings may still need heat pumps. Compare measured source and network temperatures with the required exchanger approach; do not assume every fifth-generation loop or third-generation network has one fixed temperature.
What does the EU directive require at 500 kW and at 1 MW?
Article 12 requires data centres with installed IT power demand of 500 kilowatts or more to publish the information in Annex VII and report it to the European database. Article 26 requires data centres with a total rated energy input above 1 megawatt to use the waste heat or apply other recovery measures, unless a cost-benefit analysis shows this is not technically or economically feasible.
What ERF does German law require, and when?
For German data centres beginning operation from 1 July 2026, EnEfG §11 sets at least 10% reused energy and PUE no higher than 1.2. The planned reuse share rises to 15% for facilities beginning from 1 July 2027 and 20% from 1 July 2028; the requirements are due as an annual average no later than two years after commissioning. The law also contains conditional exceptions.
Does heat pump electricity count against the German PUE limit?
EnEfG §11 excludes electricity used by plant serving only to upgrade the data centre's waste heat from the statutory PUE calculation. It still consumes electricity and affects cost and emissions.
Why does summer matter to a heat reuse project?
Data-centre heat may be available outside the heating season, while local space-heating demand often falls. ERF is based on annual energy reused, so hourly demand and system availability are needed; a winter peak is insufficient.
Sources
- European Commission — COM(2026) 500 final: energy efficiency of data centres in the EU
- Bundesministerium der Justiz — Energieeffizienzgesetz (EnEfG), § 11 Klimaneutrale Rechenzentren
- EUR-Lex — Directive (EU) 2023/1791, Articles 12 and 26
- Renewable and Sustainable Energy Reviews — Data center waste heat for district heating networks: a review
- Energy Technology (Wiley) — Survey of 53 fifth-generation district heating and cooling networks in Germany
- EUR-Lex — Delegated Regulation (EU) 2024/1364, Annex III: ERF definition
- DIN / CENELEC — DIN EN 50600-4-6 Energy Reuse Factor, November 2020 edition
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