Energy calculation as a service ECaaS
ECaaS provides an API to the Home Energy Model so users can produce software, and a basic frontend so users can validate building designs.
Energy Calculation as a Service (ECaaS) is a calculator service run by MHCLG (Ministry of Housing, Communities, and Local Government) that provides a performant implementation of the Home Energy Model (HEM), a methodology for predicting the energy performance of buildings, for various future statutory purposes including, but not limited to, calculating compliance with the Future Homes Standard (FHS).
The service takes the form of an API that can be used by authorised bodies to build software for statutory purposes that require calculations using the Home Energy Model. The service will become the only valid means to confirm compliance with Part L of the Building Regulations when referring to the Future Homes Standard. For other users, the underlying software libraries are open source and can be used to conduct calculations for non-statutory purposes.
For access to the ECaaS API contact ECaaS@communities.gov.uk
The Rust library used by ECaaS, developed within MHCLG, can be found on GitHub, and the Python implementation written by BRE under commission from DESNZ (Department of Energy Security and Net Zero) is published on BRE’s Azure DevOps space.
A basic web frontend is being developed to support stakeholders as they familiarise themselves with the HEM methodology and work out the impact on the types of home that they are building.
This article is based on the UK government "Guidance Energy calculation as a service (ECaaS): Access the Home Energy Model" published on 3 February 2025.
[edit] Related articles on Designing buildings
- Air permeability testing.
- Air tightness.
- Applying Fabric First principles: Complying with UK energy efficiency requirements FB 80.
- Approved building energy calculation software.
- Approved documents.
- Building Regulations.
- Building Research Establishment.
- Brief notes on proposed changes to EPCs.
- Changes in SAP 10.
- Co-heating test.
- Conventions for U-value calculations (2006 edition) BR 443.
- Dynamic Simulation Model.
- Emission rates.
- Energy efficiency of traditional buildings.
- Energy Performance Certificates.
- Energy Performance of Buildings Directive.
- Home Energy Model comparisons: SAP 10.2, PHPP, ESP-r and the new HEM.
- IHBC responds to Energy Company Obligation ECO4 and PAS 2035.
- Minimum energy efficiency standard (MEES).
- National Calculation Method.
- Passivhaus vs SAP.
- Standard Assessment Procedure SAP.
- Simplified Building Energy Model.
- Target fabric energy efficiency rate.
- The Home Energy Model and Future Homes Standard assessment wrapper.
- Thermal dynamic analysis.
- U-value conventions in practice: Worked examples using BR 443.
- What is the new Home Energy Model or HEM?.
Featured articles and news
Retired firefighter cycles world to raise Grenfell funds
Leaving on 14 June 2025 Stephen will raise money for youth and schools through the Grenfell Foundation.
Key points for construction at a glance with industry reactions.
Functionality, visibility and sustainability
The simpler approach to specification.
Architects, architecture, buildings, and inspiration in film
The close ties between makers and the movies, with our long list of suggested viewing.
SELECT three-point plan for action issued to MSPs
Call for Scottish regulation, green skills and recognition of electrotechnical industry as part of a manifesto for Scottish Parliamentary elections.
UCEM becomes the University of the Built Environment
Major milestone in its 106-year history, follows recent merger with London School of Architecture (LSE).
Professional practical experience for Architects in training
The long process to transform the nature of education and professional practical experience in the Architecture profession following recent reports.
A people-first approach to retrofit
Moving away from the destructive paradigm of fabric-first.
International Electrician Day, 10 June 2025
Celebrating the role of electrical engineers from André-Marie Amperè, today and for the future.
New guide for clients launched at Houses of Parliament
'There has never been a more important time for clients to step up and ...ask the right questions'
The impact of recycled slate tiles
Innovation across the decades.
EPC changes for existing buildings
Changes and their context as the new RdSAP methodology comes into use from 15 June.
Skills England publishes Sector skills needs assessments
Priority areas relating to the built environment highlighted and described in brief.
BSRIA HVAC Market Watch - May 2025 Edition
Heat Pump Market Outlook: Policy, Performance & Refrigerant Trends for 2025–2028.
Committing to EDI in construction with CIOB
Built Environment professional bodies deepen commitment to EDI with two new signatories: CIAT and CICES.
Government Grenfell progress report at a glance
Line by line recomendation overview, with links to more details.
An engaging and lively review of his professional life.
Sustainable heating for listed buildings
A problem that needs to be approached intelligently.
50th Golden anniversary ECA Edmundson apprentice award
Deadline for entries has been extended to Friday 27 June, so don't miss out!
CIAT at the London Festival of Architecture
Designing for Everyone: Breaking Barriers in Inclusive Architecture.
Mixed reactions to apprenticeship and skills reform 2025
A 'welcome shift' for some and a 'backwards step' for others.