What is PAS 2035 is (and why must ECO4 adhere to it)?

PAS 2035 sets the rules for domestic retrofit: how homes are assessed, designed, coordinated, and evaluated. Installations themselves must be done to PAS 2030. For ECO4 projects, the two work together: designs to PAS 2035, installations to PAS 2030.

What counts as success

• Lower energy use and reduced heating costs.
• Warmer, healthier homes (IAQ, damp/mould elimination, comfort).
• Reduced carbon emissions and climate resilience.
• Protection of heritage where relevant.

Who does what (accountability)

Retrofit Coordinator

Leads the project from day one to handover. Agrees intended outcomes, oversees assessment, commissions design, checks installation is to spec, records non‑compliance, and ensures monitoring & evaluation.

Retrofit Assessor

Whole‑dwelling assessment: building condition & defects, energy model (SAP/RdSAP/PHPP), ventilation & moisture checks, occupancy & fuel costs, heritage/planning constraints.

Retrofit Designer

Creates the retrofit design: package of measures, sequencing, ventilation strategy, airtightness targets/details, technical drawings/specs and site instructions.

Installer (PAS 2030)

Installs measures to PAS 2030 (or MCS where applicable), follows the design exactly, attends briefings/toolbox talks, provides test/commissioning records and handover documents.

Retrofit Evaluator

Checks whether outcomes were actually delivered (basic evaluation on every job; deeper monitoring if issues arise or as per plan).

The retrofit process (what you should see)

1. Inception — Coordinator appointed; objectives agreed (e.g., reduce bills, eliminate damp).
2. Whole‑dwelling assessment — thorough survey incl. ventilation, moisture, energy model and defects.
3. Improvement options evaluation — Coordinator compares packages by bill savings & CO₂ impact.
4. Medium‑Term Improvement Plan — the long‑term, staged plan (20‑30 years), with sequencing & monitoring.
5. Design & specification — drawings, details, ventilation strategy, airtightness target, tests & commissioning plan.
6. Installation — installed to PAS 2030/MCS; site briefings; quality control.
7. Testing, commissioning & handover — airtightness/flows, settings, manuals, warranties, homeowner advice.
8. Monitoring & evaluation — basic evaluation for every job; deeper monitoring if results look off.

Distressed replacements: If a heating system fails mid‑winter, urgent replacement can happen — but the project must still be brought into full PAS 2035 compliance as soon as possible.

Special requirements you’re entitled to

• Moisture & ventilation managed to modern standards (avoid mould/condensation/IAQ issues).
• Airtightness strategy (with leakage testing where required), not just insulation everywhere.
• Climate resilience considered (overheating, flood risk, future climate).
• Traditional/protected buildings: added heritage assessments and careful measure selection.
• Retrofit advice at multiple stages so you can run the home efficiently after works.

How PAS 2035 fits with other rules

Related standards & guidance

PAS 2030 (Installers)

Sets the workmanship rules for installing measures. ECO4 projects must use PAS 2030‑certified installers (or MCS for relevant microgeneration).

Building Regulations

Safety, ventilation, structure, fire, electrics etc. Retrofit must also comply with the Building Regs (e.g., Approved Document F for ventilation).

TrustMark Framework

Government‑endorsed quality scheme. ECO4 jobs are registered with TrustMark and must comply with its Consumer Charter and Code of Conduct.

Key technical references

• BS 5250 — Moisture in buildings (condensation & mould risk management).
• BS 7913 — Conservation of historic buildings.
• BS 40101 — Building performance evaluation (monitoring & feedback).
• MCS standards — Where heat pumps/solar etc. are installed.
• Approved Document F – Legal requirements for ventilation in homes.

Bottom line: PAS 2035 is the process standard; PAS 2030 is the installation standard. ECO4 projects must satisfy both, plus Building Regulations and TrustMark requirements. HHCRO

How do MCS and PAS Standards Overlap?

• PAS 2035/2030 → Framework for retrofit assessment, design, coordination, and installation of energy efficiency measures (insulation, ventilation, airtightness, heating controls, etc.).
• MCS (Microgeneration Certification Scheme) → Quality standards for the design and installation of small-scale renewable technologies, e.g.:
  • MIS 3005 → Heat pumps
  • MIS 3002 → Solar thermal
  • MIS 3001 → Solar PV
  • MIS 3012 → Battery storage

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• Design stage:
  • PAS 2035 requires the Retrofit Designer/Coordinator to ensure any proposed system integrates into the “whole-house plan” (ventilation, insulation, heating demand, fuel bills).
  • If that system is a heat pump or solar, MCS standards govern the technical design and sizing (e.g. MIS 3005 heat loss calculations must match PAS whole-dwelling assessment).
• Installation stage:
  • PAS 2030 covers general workmanship and quality management.
  • If the measure is a microgeneration technology, the installer must also be MCS certified.
  • In practice: a heat pump install under ECO4 must be both PAS 2030:2019 compliant and MCS compliant.
• Consumer protection:
  • TrustMark is the umbrella scheme. PAS 2035/30 compliance is mandatory for TrustMark registration; MCS registration is mandatory for microgeneration. Both feed into TrustMark’s quality assurance framework.

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1. PAS 2035 → Retrofit Assessor produces whole-dwelling survey & heat loss model. Retrofit Coordinator agrees intended outcomes (lower bills, reduced carbon).
2. MCS MIS 3005 → Installer must use accurate heat loss calculations (often more detailed than RdSAP) to size the heat pump correctly.
3. PAS 2030 → The physical installation (pipework, insulation, commissioning) must follow PAS 2030 processes and QMS.
4. Overlap point → If the heat pump is oversized/undersized, or if the retrofit fabric work isn’t done first, the install breaches both PAS 2035 (whole-house methodology) and MCS MIS 3005 (technical sizing).

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If a household is left with high bills or an unheatable home:

• PAS breach: Coordinator failed to ensure outcomes (e.g. affordable heating).
• MCS breach: Installer failed to design/size system correctly under MIS standards.
• TrustMark breach: Failure to comply with either standard undermines consumer protection obligations.

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👉 In plain terms: PAS covers the overall retrofit journey; MCS governs the technical details of renewable systems. Under ECO4, both must be satisfied simultaneously where relevant.

ECO4 Scheme Rules (Ofgem)

• ECO4 (the government’s Energy Company Obligation scheme) requires energy suppliers to fund measures that cut carbon emissions and help households in fuel poverty.
• The rules specifically say that every funded retrofit must aim to reduce heating costs for the household.
• Under PAS 2035, this translates into a design obligation: Retrofit Coordinators must set intended outcomes such as lower fuel bills, elimination of damp, and improved comfortPAS2035_2023.
• In practice, this means installers cannot just fit a heat pump or insulation if it leaves the home more expensive to run — the measures must demonstrably make the home cheaper to heat.

Home Heating Cost Reduction Obligation — the ECO4 bill‑cutting duty (HHCRO)

Under ECO4, energy suppliers have a single statutory duty: deliver home heating cost reduction for eligible (especially low‑income and vulnerable) households. This is known as the Home Heating Cost Reduction Obligation (HHCRO).

What it means for you

• Works must demonstrably reduce your actual heating costs.
• Purpose is warmer homes, lower bills, and lower carbon — not just ticking technical boxes.
• Suppliers are measured using Annual Bill Savings (ABS) targets across the measures they install.

Responsibility chain

The legal obligation sits with the energy supplier, but their delivery partners and installers share responsibility to ensure each measure contributes to HHCRO and does not leave households worse off.

If your bills rise after ECO4, that’s a red flag for non‑compliance.

Ready‑to‑use complaint wording (copy & paste)

Failure to Comply with the Home Heating Cost Reduction Obligation (HHCRO)
Under ECO4, obligated energy suppliers and their delivery partners are required to comply with the Home Heating Cost Reduction Obligation (HHCRO). This statutory obligation requires that installations deliver measurable reductions in household heating costs for eligible households. In my case, the installation carried out by Consumer Energy Solutions (CES), acting as a subcontractor within a supplier’s ECO4 delivery chain, has failed to deliver the intended reduction in home heating costs. Instead, the works have left my household with higher energy bills / an unheatable home / continued fuel poverty [adapt]. This outcome is contrary to ECO4 guidance and the scheme’s purpose to alleviate fuel poverty by reducing actual home heating costs. The installation therefore fails the statutory test of compliance with HHCRO.

Tip: attach evidence such as pre/post energy bills, heating run‑time/flow‑temp data, photos of defects, and any ventilation/airtightness test results.

Practical Strategy

I’d recommend a multi-pronged approach:

1. Installer (CES) – put them on notice with the HHCRO failure wording.
2. Supplier – state that their statutory HHCRO duty has not been met.
3. TrustMark – file a complaint citing PAS 2035/2030 and HHCRO breach.
4. Ofgem – send a copy with evidence (bills, assessments, lived experience) to show the failure impacts Annual Bill Savins (ABS delivery).

Copyright & fair‑use note

PAS 2035 and PAS 2030 are copyrighted by BSI.
This page provides a plain‑English summary to help households understand their rights and obligations without reproducing BSI’s material.

Last updated: 9 September 2025 • This page summarises public standards & scheme rules for guidance only and is not legal advice.