Guidance

HNTAS: Existing heat networks - draft assessment procedures for Milestone 4

Draft procedures that Heat Network Technical Assurance Scheme (HNTAS) registered assessors will need to follow to assess a heat network’s compliance with HNTAS technical requirements.

• From: Department for Energy Security and Net Zero
• Published: 5 January 2026

Applies to England, Scotland and Wales

Documents

DRAFT: HNTAS existing heat network assessment procedure Milestone 4 - Energy Centres

Ref: HNTAS-EX-AP-EC-M4

PDF, 337 KB, 16 pages

DRAFT: HNTAS existing heat network assessment procedure Milestone 4 - District Distribution Networks

Ref: HNTAS-EX-AP-DD-M4

PDF, 336 KB, 15 pages

DRAFT: HNTAS existing heat network assessment procedure Milestone 4 - Substations

Ref: HNTAS-EX-AP-SS-M4

PDF, 334 KB, 15 pages

DRAFT: HNTAS existing heat network assessment procedure Milestone 4 - Communal Distribution Networks

Ref: HNTAS-EX-AP-CD-M4

PDF, 337 KB, 16 pages

DRAFT: HNTAS existing heat network assessment procedure Milestone 4 - Consumer Connections

Ref: HNTAS-EX-AP-CC-M4

PDF, 338 KB, 16 pages

Details

These draft assessment procedures for existing heat networks detail the activities to be undertaken to verify compliance with Milestone 4 requirements in the upcoming Heat Network Technical Assurance Scheme (HNTAS).  They cover the requirements to achieve HNTAS Certification 1.

The documents are for use by:

• heat network assessors
• heat network operators

These assessment procedures correspond to the draft HNTAS technical specifications for Milestone 4.

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.

Published 5 January 2026