The ECO4 grant covers windows only when they are part of a whole-house energy-efficiency package
The Energy Company Obligation (ECO4) scheme, administered by Ofgem, is designed for low-income and vulnerable households to improve the overall energy performance of their homes (Ofgem, 2026). It is not a window replacement grant. Single-glazed windows can be replaced under ECO4, but only if the home also receives at least one other primary measure, such as loft insulation, cavity wall insulation, or a new heating system. The window replacement must be justified by the property’s Energy Performance Certificate (EPC) and the modelled energy savings calculated by the installer (Ofgem, ECO4 Guidance: Delivery, 2026).
Yes, but only as part of a whole-house package. ECO4 covers single-glazed or pre-2002 double-glazed windows when paired with another primary measure like insulation or a new heating system. Check eligibility via Ofgem.
- ECO4 covers windows only as a secondary measure with another primary upgrade.
- Single-glazed or pre-2002 double glazing may qualify for replacement.
- Households must receive a qualifying benefit or meet LA Flex criteria.
- Window replacement must achieve a minimum U-value of 1.2 W/m²K.
- Apply through an Ofgem-approved installer for a whole-house retrofit plan.
- The ECO4 grant covers windows only when they are part of a whole-house energy-efficiency package
- The key difference between ECO4 and the previous ECO3 scheme for window replacements
- The specific eligibility criteria for window replacement under ECO4
- Quick numbers Typical costs and savings for ECO4 window replacements
- How to verify an installer and ensure your window replacement is ECO4-compliant
- The direct answer Does the ECO4 grant cover windows?
- What the ECO4 grant does NOT cover for windows
The key difference between ECO4 and the previous ECO3 scheme for window replacements
Under ECO3, windows were a standalone measure for certain households; under ECO4, they are always a secondary or tertiary measure. ECO4 requires a minimum of two measures per property, with windows only eligible as part of a broader upgrade plan (DESNZ, ECO4 Final Stage Impact Assessment, 2022). The shift was intended to ensure whole-house retrofits rather than piecemeal upgrades, aligning with the UK’s net-zero targets. This means homeowners cannot apply for ECO4 purely to replace windows. The window work must be tied to a larger retrofit project, such as cavity wall insulation plus a new boiler, with windows added as an additional measure.
The specific eligibility criteria for window replacement under ECO4
The property must have single glazing or poorly performing double glazing (installed before 2002) to qualify. The household must be in receipt of a qualifying benefit (e.g., Pension Credit, Universal Credit, Child Tax Credit) or meet the local authority flexible eligibility (LA Flex) criteria (Ofgem, ECO4 Guidance: Measures and Costs, 2023). The window replacement must achieve a minimum U-value of 1.2 W/m²K for new double-glazed windows (Energy Saving Trust, Window Energy Ratings, 2026). U-value measures heat loss; lower numbers mean better insulation. Installers must calculate the energy savings using Ofgem’s deemed scores methodology, which compares the existing window performance to the new specification.
Quick numbers Typical costs and savings for ECO4 window replacements
| Measure | Average cost (without grant) | Annual energy saving (kWh per window) | Grant coverage |
|---|---|---|---|
| Single glazing replaced with double glazing (U-value 1.2) | £600–£1,200 | 80–120 kWh | Up to 100% for qualifying households |
| Old double glazing (pre-2002) replaced with modern double glazing | £500–£1,000 | 40–70 kWh | Up to 100% for qualifying households |
| Single glazing replaced with triple glazing | £800–£1,500 | 100–150 kWh | Up to 100% for qualifying households |
| Secondary glazing added to single glazing | £200–£500 | 50–80 kWh | Not covered under ECO4 |
Costs are industry estimates and vary by region, window size, and frame material (Energy Saving Trust, 2026). The grant covers the full cost for qualifying households, but only if the installer’s assessment shows the window replacement delivers sufficient energy savings relative to the overall package (Ofgem, ECO4 deemed scores methodology, 2023).
How to verify an installer and ensure your window replacement is ECO4-compliant
All ECO4 installations must be carried out by an MCS-certified installer for the primary measures, and window installers must be FENSA-registered or equivalent (e.g., CERTASS) (Ofgem, ECO4 Guidance: Installer Requirements, 2023). The installer must produce a full retrofit assessment, including an EPC and a room-by-room heating plan, before work begins. Homeowners should check the MCS register (MCS, 2026) and FENSA register (FENSA, 2026) for installer credentials. If the installer is not registered, the work will not be eligible for ECO4 funding. How to check if an installer is MCS certified
The direct answer Does the ECO4 grant cover windows?
Yes, but only as part of a whole-house retrofit package that includes at least one other primary energy-efficiency measure (Ofgem, ECO4: Frequently Asked Questions, 2026). The window replacement must be for single glazing or very old double glazing, and the household must meet the eligibility criteria for ECO4. The grant covers the full cost of the window replacement for qualifying households, subject to the installer’s assessment and Ofgem’s approval. You cannot receive funding for windows alone; they are always a secondary measure in a broader retrofit plan.
What the ECO4 grant does NOT cover for windows
The grant does not cover decorative or non-energy-saving window upgrades, such as bay windows, stained glass, or purely cosmetic replacements (Ofgem, ECO4 Guidance: Excluded Measures, 2023). It does not cover windows in properties that already have efficient double or triple glazing (U-value below 1.2 W/m²K). It does not cover windows that are part of a new extension or conservatory, as these are not considered energy-efficiency improvements to the main dwelling. The grant does not cover repairs to existing windows, such as replacing a single broken pane, unless the entire window is being upgraded to meet the U-value standard. What the ECO4 grant covers and excludes
