How Heat Networks Work Under the FHBS
Heat networks will play an important part in the UK's net zero future. The government has set out two compliance routes for new buildings connected to heat networks, supporting their expansion where they are making demonstrable steps to decarbonise.
Compliance Routes for Heat Network Buildings
Route 1: Low-Carbon Heat Network Notional Building
For single-building (communal) networks, compliance is demonstrated by comparing the building's performance against a standardised low-carbon heat network notional building. This route is available where very low-carbon district-level heat networks can offer heat that outperforms the notional standard, benefiting the dwelling's overall emissions and primary energy. The methodology follows previous iterations of Part L, reflecting the heat network's specific heat generating plant type(s) and efficiencies.
Route 2: Sleeving Approach
For district heat networks supplying multiple buildings, at least 90% of the thermal energy delivered to the new building (in kWh over a year, including distribution losses) must be provided by low-carbon heat sources. Up to 10% can be provided by other sources. A heat network operator makes a declaration verified by a suitably qualified third party. This removes the heat network's performance from the compliance calculation — only the building's other aspects (insulation, lighting) affect whether targets are met.
Future Route 3: Passporting (Planned)
Once heat network zoning regulations under the Energy Act 2023 are in place, a third compliance route may be introduced. A heat network could receive a "passport" when its emissions are being controlled under other legislation, such as a heat network zoning emissions limit. The government intends to review and amend the Approved Documents to align with this legislation.
Important Requirements for Heat Network Connections
Temporary Heating Must Be Low-Carbon
When new buildings are constructed with the intention of connecting to a heat network but cannot connect immediately, temporary heating may be required. The FHBS requires that temporary heating solutions must be low-carbon — fossil fuel temporary systems will not demonstrate compliance. This prevents "temporary" fossil fuel systems from being left in place permanently.
5-Year Connection Window
Under the sleeving method, heat networks have 5 years to connect clean energy sources. This was extended from the originally consulted 3-year window, providing additional flexibility whilst still requiring demonstrable progress towards decarbonisation.
Communal vs District Networks
Communal heat network systems — where multiple dwellings within a single building are served from a central heat source in that building — cannot use the sleeving route. They must use Route 1 (the notional building approach). The sleeving approach is only available for district heat networks supplying multiple separate buildings.
Heat Network Questions
Can new FHS homes connect to existing heat networks?
Yes, provided the heat network can demonstrate sufficient low-carbon heat generation. Under the sleeving approach, at least 90% of thermal energy delivered to the new building must be from low-carbon sources. The heat network operator must provide a verified declaration to building control as part of the compliance process.
What happens if the heat network isn't ready when the building is completed?
Temporary heating solutions may be used, but they must be low-carbon. Fossil fuel temporary systems will not meet FHBS compliance. This ensures all new buildings are low-carbon from occupation and prevents temporary fossil fuel systems from becoming permanent.