Mode London connects to E.ON’s City heat network

City of London tower becomes first building on E.ON Citigen sleeved connection

E.ON has connected Mode London, the postmodernist office tower at 125 London Wall, to its Citigen district heat network using a new supply arrangement. The deal marks the first time the network has provided a direct connection from its central energy plant. It also establishes a partnership running through to the 2040s.

Mode London is an 18-floor office building designed by Sir Terry Farrell and completed in 1992. The building is currently undergoing major refurbishment to deliver 340,000 square feet of workspace targeting WELL Platinum certification and an EPC B rating. The project includes multiple private terraces, a 5,000 square foot club lounge, wellness facilities, and landscaped roof gardens.

The building sits between Moorgate, St Paul’s, Barbican, Farringdon, and Liverpool Street stations. Its location near the Elizabeth Line and cultural venues like the Barbican Centre makes it attractive to finance and technology occupiers. Mode London consumes up to 2.4 gigawatts of heat each year.

How the Citigen network supplies low-carbon heat beneath the Square Mile

E.ON’s Citigen network operates 12 kilometres of underground pipes beneath the City of London. The system serves buildings from Smithfield Market to the Barbican estate. It generates renewable energy equivalent to the needs of 13,600 homes and businesses across the Square Mile.

In 2023, Citigen completed a £4 million upgrade including ground source heat pumps and borehole storage reaching 200 metres underground. The system captures waste heat from cooling processes and recycles it to provide heating elsewhere on the network. This approach eliminates the need for fossil fuel combustion at connected buildings.

The network delivers both heating and cooling depending on seasonal demand. Heat pumps extract thermal energy from boreholes during winter months. During summer, the system provides chilled water for air conditioning while storing excess heat underground for later use.

Consequently, buildings connected to Citigen can reduce their direct carbon emissions substantially. They also benefit from improved energy resilience compared to standalone gas boilers or electric heating systems.

Mode London refurbishment timeline and technical specifications

Arax Properties owns Mode London, with Collins Construction delivering the refurbishment works. The podium construction phase will complete in the first quarter of 2025. Category A office floors will become available from early 2026, with full leasing starting on 1 April 2026.

The building offers flexible floorplates ranging from 14,000 to 28,000 square feet. Current availability stands at approximately 189,768 to 229,752 square feet, with rental values around £69.50 per square foot. The all-electric design eliminates gas infrastructure entirely.

Amenities include 253 lockers, 244 cycle parking spaces, and 31 showers for active commuters. The building provides exceptional electrical capacity to support high-density office fit-outs and technology requirements. Rooftop terraces and ground-floor landscaping create outdoor workspace and break areas.

Moreover, the refurbishment targets CRREM alignment, which assesses whether commercial buildings meet science-based decarbonisation pathways. This certification matters increasingly to institutional investors and occupiers with net-zero commitments. The project also incorporates circular economy principles in material selection and waste management.

What makes this connection different from standard heat network supplies

The agreement uses a “sleeved” supply arrangement rather than a conventional connection. This means heat travels directly from Citigen’s central heat pumps to Mode London without mixing with other network flows. The approach delivers a dedicated low-carbon heat source that improves the building’s energy performance rating.

Traditional district heating connections draw from a shared network loop where heat from multiple sources combines. A sleeved connection maintains a separate circuit, allowing precise tracking of the energy source and carbon intensity. This distinction helps building owners demonstrate compliance with increasingly stringent environmental standards.

Furthermore, Mode London’s proximity to the existing Citigen infrastructure made this connection method viable without major above-ground works. Engineers could link the building to the network beneath London Wall with minimal disruption to traffic and businesses. This reduced both cost and construction risk compared to extending pipes across longer distances.

The arrangement provides operational flexibility for both parties. E.ON can manage heat pump capacity more efficiently when serving a large baseload customer. Mode London gains supply certainty and transparent carbon accounting for tenant reporting requirements.

Essential details about the Mode London heat connection

• The sleeved connection arrangement represents the first of its kind on the Citigen network, establishing a model for future large building connections across the City of London.
• Mode London will receive low-carbon heat sufficient for 2.4 gigawatts of annual consumption, supporting its target EPC B rating and WELL Platinum certification goals.
• The partnership extends for 20 years into the 2040s, providing long-term energy cost visibility for prospective tenants and building owners.
• Podium construction completes in Q1 2025, with Category A office space available from Q1-Q2 2026 and full leasing commencing on 1 April 2026.
• The building offers between 189,768 and 229,752 square feet across floorplates of 14,000 to 28,000 square feet, with rental values around £69.50 per square foot.
• Citigen’s 2023 upgrade included £4 million investment in ground source heat pumps and borehole thermal storage reaching 200 metres depth for zero-carbon heat generation.
• The connection required no above-ground disruption due to Mode London’s location adjacent to existing Citigen infrastructure beneath London Wall.

Why district heating matters for commercial property in central London

Heat networks like Citigen help commercial landlords meet rising environmental standards without costly individual building plant upgrades. Connecting to a district system eliminates the need for on-site boilers, reduces maintenance requirements, and frees up valuable plant room space for alternative uses.

Tenant demand for low-carbon buildings continues to grow, particularly among financial services and technology firms with corporate sustainability commitments. Buildings without credible decarbonisation pathways face growing obsolescence risk as occupiers prioritise EPC ratings and Scope 2 emissions in location decisions.

The Energy Act 2023 aims for heat networks to supply 20 percent of UK heat demand by 2050. London’s geography and building density make district heating particularly viable in central areas. The Greater London Authority has commissioned multiple studies examining heat network expansion potential across the capital.

Waste heat recovery offers significant potential. Studies suggest that recoverable waste heat from London’s commercial and industrial processes could meet 38 percent of the city’s total heat demand. District heating infrastructure makes this recovery economically and technically practical at scale.

Additionally, heat networks improve energy resilience compared to buildings dependent on national gas or electricity grids. Local generation and storage capacity can maintain service during supply interruptions. This matters increasingly as extreme weather events affect energy infrastructure more frequently.

How Mode London demonstrates commercial real estate decarbonisation

Mode London’s refurbishment shows how existing commercial stock can achieve modern environmental standards through strategic infrastructure decisions. Connecting to Citigen avoided the complexity and cost of installing and operating on-site low-carbon heat generation equipment.

The all-electric design eliminates combustion emissions entirely from the building. This simplifies carbon reporting for tenants and ensures compliance with strengthening building regulations. The approach aligns with the City of London’s environmental targets and broader UK net-zero commitments.

CRREM alignment matters because it provides a science-based benchmark for decarbonisation progress. Buildings that fail to meet CRREM pathways risk becoming stranded assets as investors apply climate risk assessment to property portfolios. Early action on decarbonisation protects asset values over the medium term.

The WELL Platinum certification target addresses occupant health and wellbeing through air quality, lighting, thermal comfort, and acoustic performance. Research shows that buildings with strong wellness credentials achieve higher occupancy rates and rental premiums. Consequently, combining environmental and wellness certifications strengthens the investment case for deep refurbishment.

This project illustrates how heat network connections can deliver carbon reduction without compromising building functionality or tenant experience. The system operates invisibly to occupiers while substantially reducing the building’s operational carbon footprint. This combination appeals to corporate occupiers balancing sustainability goals with practical workspace requirements.

E.ON’s broader district heating strategy beyond Citigen

E.ON is developing heat network projects across multiple UK cities. The Ectogrid development at Silvertown in east London will eventually serve 6,500 homes and businesses. This project uses a different technical approach from Citigen, operating at lower temperatures to capture waste heat from diverse sources including industrial processes, data centres, and the London Underground.

The company has studied district heating systems in European cities including Malmö and Berlin. These mature networks demonstrate how heat infrastructure can evolve over decades, progressively incorporating lower-carbon heat sources as technology advances and renewable energy becomes cheaper.

Heat networks offer particular advantages in dense urban areas where individual building solutions prove impractical or expensive. They enable pooling of heat demand across residential, commercial, and public sector customers. This diversity improves network economics by balancing different usage patterns throughout the day and year.

E.ON’s investment in the Citigen upgrade reflects confidence in long-term heat network policy support. The Energy Act 2023 provides regulatory frameworks for heat network development, pricing, and consumer protection. This certainty encourages the long-term capital investment required for major infrastructure projects.

Moreover, heat networks create opportunities for integrating intermittent renewable electricity generation. Heat pumps can operate when renewable power is abundant and cheap, storing thermal energy for later use. This flexibility helps balance electricity grids with high renewable penetration, supporting overall system decarbonisation.

Implications for UK businesses considering low-carbon heat options

Commercial property occupiers should consider heat network availability when evaluating office locations. Buildings with district heating connections typically offer lower operating costs and superior environmental performance compared to gas-heated alternatives. These factors increasingly influence corporate real estate decisions.

For building owners, district heating connections can improve asset valuations by reducing obsolescence risk. Properties meeting current and anticipated environmental standards command rental premiums and attract longer lease commitments. Conversely, buildings reliant on fossil fuel heating face mounting regulatory and market pressures.

Businesses in areas without existing heat networks should monitor local authority heat network zoning plans. Many councils are mapping heat demand and identifying priority areas for network development. Early engagement can influence infrastructure planning and secure advantageous connection terms.

Heat network connections require careful contract review. Key considerations include supply reliability guarantees, carbon intensity commitments, price escalation mechanisms, and connection cost allocation. Professional advice helps ensure agreements deliver intended carbon and cost benefits over the contract term.

The Mode London deal demonstrates that major commercial refurbishments can integrate heat network connections without excessive disruption or cost. This experience may encourage other City of London landlords to investigate Citigen connections as existing plant reaches end of life. The cumulative effect could substantially accelerate commercial property decarbonisation across the Square Mile.

Furthermore, businesses developing carbon reduction strategies for PPN 06/21 compliance should recognise that building energy infrastructure increasingly determines achievable emissions reductions. Facilities in buildings with low-carbon heat supplies can report lower Scope 2 emissions, improving overall corporate carbon performance.

Further reading

The Department for Energy Security and Net Zero publishes guidance on heat network policy, regulation, and development programmes. Their resources explain how the Energy Act 2023 affects heat network operators and connected customers.

The Greater London Authority heat network programme provides information specific to London’s district heating infrastructure. The site includes maps of existing networks, planned developments, and heat demand data for different areas of the capital.

The Chartered Institution of Building Services Engineers maintains technical guidance on heat network design, operation, and connection standards. This material helps businesses understand technical requirements when evaluating heat network options.

For businesses seeking support with environmental compliance and carbon reporting, specialist consultancies can assess how building energy infrastructure affects achievable emissions reductions and regulatory obligations.

Property owners and occupiers can also access training on environmental building standards to understand how heat networks and other low-carbon technologies contribute to certifications like BREEAM, WELL, and NABERS UK.