Guidance

HNTAS: Existing heat networks - draft technical specifications for Milestone 3B

Draft Heat Network Technical Assurance Scheme (HNTAS) regulatory technical requirements to help heat network operators demonstrate compliance.

Applies to England, Scotland and Wales

Documents

Details

This draft technical specification for existing heat networks details the requirements and technical obligations to be fulfilled at Milestone 3B as part of the upcoming Heat Network Technical Assurance Scheme (HNTAS).

Milestone 3B sets out metering and monitoring requirements for existing networks which were not previously required to have metering installed under Heat Network Metering and Billing Regulations (HNMBR) 2014.

Milestone 3B only applies to the consumer connection element.

The document covers the:

  • technical requirements to be met 
  • performance monitoring requirements to be met 
  • key failures to be avoided
  • evidence requirements to be provided to demonstrate conformity with HNTAS

It is for use by:

  • heat network operators
  • organisations within the heat network supply chain

This technical specification corresponds to the draft HNTAS assessment procedures for Milestone 3B.

Next steps

We will be requesting feedback on the information in these documents. We will run a change management process in parallel with the HNTAS technical standards consultation which will launch shortly.

We will make final versions of these documents available before the scheme starts.

Updates to this page

Published 5 January 2026

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