Introducing the Vulcan API: a scheme-grade path to HEM compliance

The Home Energy Model (HEM) is the planned successor to SAP for UK domestic building regulations. Regulatory use of HEM is facilitated by a UK Government API (ECaaS) and moderated by Energy Assessor Schemes: organisations that train assessors, check competence, and quality-assure assessments before they reach the public register.

At the end of 2025, Vulcan became an Energy Assessor Scheme. Today we're opening those scheme-grade workflows up to other products.

The Vulcan API

The UK market isn't short of energy modelling tools.

The Vulcan API lets third-party software connect to Vulcan's scheme workflows — so your users can draft lodgements, upload evidence, request reviews, and submit for compliance checks without leaving your product. Vulcan handles the scheme governance: assessor qualification, evidence sharing, review, regulatory lodgement, and quality assurance.

Who this is for

If you build software for heat pump sizing, retrofit optimisation, portfolio modelling, assessor workflows, or housebuilder design portals, the API lets you add HEM compliance to your product. Your users don't need to switch tools, re-enter data, or manually piece together evidence trails.

What the API covers

The API covers the Lodge workflow — the journey from draft to regulatory submission:

1. Create a draft lodgement with dwelling and plot metadata
2. Upload evidence (photos, documents, certificates) via presigned URLs
3. Request review feedback at a draft stage from a Vulcan reviewer (optional)
4. Submit for compliance — Vulcan runs the ECaaS check on your behalf
5. Poll for results until the submission succeeds or fails

A training mode lets you build and test your integration without affecting live data.

How authentication works

The API uses OAuth2 client credentials for machine-to-machine auth and a consent flow (PKCE) for linking end users.

1. Register as an API partner — contact Vulcan to receive a client_id and client_secret.
2. Get an access token — exchange your credentials for a short-lived Bearer token.
3. Link a user — redirect the user to Vulcan's consent page (OAuth2 PKCE). Once they grant access, you receive an authorisation code to complete the link.
4. Make API calls — pass the Bearer token and an X-External-User-Id header on every request.

Access tokens carry scopes (e.g. lodgements:write, evidence:write, submissions:read) so you can request only the permissions your integration needs.

What you get out of the box

The API is designed to make integrations reliable from day one:

• Consistent response shapes — every endpoint returns { data, meta } on success and { error, meta } on failure, with an RFC 7807 error structure
• Request IDs — every response includes an X-Request-Id header for tracing and support
• Idempotency — create and submit operations accept an Idempotency-Key header, so retries are safe
• Rate limiting — X-RateLimit-Remaining and Retry-After headers let integrations back off gracefully
• Capability discovery — GET /v1/capabilities returns your client's limits, supported values, and permissions so you can adapt your UI dynamically

Pricing

There are two separate costs:

For API partners (the organisation integrating with Vulcan):

• Enterprise plan — £1,000/month, includes API credentials, 1 software seat, integration onboarding, and priority support

For API users (the energy assessors who use the integration):

Each user linked through the API must have Vulcan Scheme access. Two options:

• Member — £100/month, includes Vulcan software, OCDEA accreditation, training, and 50 lodgements per month
• Pay-as-you-go — £5 per lodgement, no monthly commitment

Users can sign up at usevulcan.app/join, or be linked to an existing account through the API's consent flow.

Documentation

Full API documentation is available at api.usevulcan.app/docs.

What's next

HEM is evolving, and so will the ecosystem around it. Our goal is to make that evolution safer and faster by giving software teams a stable interface for regulatory workflows, so they can continue to innovate.

Read the API documentation, or get in touch to discuss your integration.