ECO4, HUG2, and GBIS Eligibility: How to Get Free Windows and Insulation

ECO4 has allocated over £4 billion of energy company obligation funding. The scheme covers window replacement for qualifying households — but you cannot apply for windows alone, and most people who think they qualify do not pass all three eligibility gates.

The grant-farm sites skip that detail. Three schemes matter: ECO4, HUG2, and the Great British Insulation Scheme (GBIS). They have different qualifying criteria, different funding sources, and different rules on what they will and will not pay for. Getting the sequencing wrong wastes months.

Grant Stacking Table: Which One applies to You?

Scheme	Primary Focus	Qualifying EPC	Funding Source	Target Group
ECO4	Whole-House Retrofit	D $\rightarrow$ G	Energy Suppliers	Low-income / Fuel Poor
HUG2	Fabric-First (Insulation)	D $\rightarrow$ G	Gov / Suppliers	Low-income / Vulnerable
GBIS	Single Insulation Measure	D $\rightarrow$ G	Gov / Suppliers	Inefficient Homes (EPC D-G)

The “Whole-House” Logic of ECO4

ECO4 takes a whole-house approach, unlike every scheme before it. You cannot apply for windows in isolation. The windows must form part of a package designed to lift the property’s EPC rating — which typically means loft insulation, cavity wall insulation, or a boiler upgrade happening at the same time.

If your home has an EPC rating of D, E, F, or G, you are the primary target for ECO4. The funding is provided by energy suppliers who are mandated by the government to hit carbon reduction targets. To qualify, you are usually required to be on certain benefits or meet low-income thresholds.

Great British Insulation Scheme (GBIS): The “Quick Win”

If you don’t meet the strict low-income criteria for ECO4, you might still qualify for GBIS. This scheme targets the “efficiency gap”—homes that are inefficient (EPC D-G) but not necessarily “fuel poor.”

GBIS Eligibility Quick-Check:

• EPC Rating: Must be D, E, F, or G.
• Council Tax Band:
  • England: Bands A-D.
  • Scotland & Wales: Bands A-E.
• Measure: Focuses on single insulation measures (e.g., loft or cavity wall), but this often creates the thermal baseline required to then justify window upgrades through other funding.

HUG2: The “Fabric First” Layer

The Home Upgrade Grant (HUG2) is designed to “top up” ECO4. It provides funding for those who have already had some improvements but still have “cold spots” in their home. It is specifically focused on the “fabric first” approach—insulating the shell of the building before upgrading the heating system.

HUG2 is particularly relevant for off-gas-grid homes—properties that rely on electric, oil, or LPG heating and are therefore more exposed to volatile energy prices. If your home is heated by anything other than mains gas, HUG2 should be your first port of call after ECO4.

The Application Process: Step by Step

Many homeowners are deterred by the perceived complexity of grant applications. In practice, the process is straightforward if you follow the correct sequence:

1. Check your EPC rating: Visit the EPC Register (epc.register.gov.uk) and search your postcode. Your current rating determines which schemes you are eligible for.
2. Verify your benefits status: For ECO4, you must be in receipt of a qualifying benefit (Universal Credit, Pension Credit, Income Support, etc.) or meet the local authority’s flexible eligibility criteria.
3. Contact a TrustMark-registered installer: They will assess your property, confirm eligibility, and handle the grant paperwork. Using a certified installer is mandatory—not optional.
4. Sign the grant agreement: This locks in the funding and sets out what measures will be carried out.
5. Works completed: The installer carries out the measures and claims the grant directly from the energy supplier. You pay nothing (or a heavily reduced amount) at the point of delivery.

Can You Really Get Free Windows?

The honest answer is: sometimes. ECO4 can cover the full cost of window replacement in qualifying properties, but only where windows are identified as part of a whole-house retrofit plan. You cannot apply for windows alone—they must form part of a package that may also include loft insulation, cavity wall insulation, and boiler upgrades.

The typical grant value for window replacement under ECO4 ranges from £1,500 to £4,000, depending on the property size and the number of windows. This may not cover the full cost of premium products, but it substantially reduces the capital outlay.

Common Reasons Applications Fail

1. Wrong EPC rating: Properties rated A, B, or C are generally ineligible. Check before you apply.
2. Non-TrustMark installer: If your preferred installer is not TrustMark-registered, the grant cannot be claimed through them. This is the single most common reason for rejection.
3. Incomplete documentation: Missing benefit letters, outdated EPC certificates, or unsigned declarations will delay or derail the application.
4. Property already improved: If your home already has cavity wall insulation and loft insulation to current standards, the remaining carbon savings from new windows may not be sufficient to meet the scheme’s thresholds.
5. Timing: ECO4 runs until 31 December 2026 (with the nine-month extension already applied by Ofgem). Funding tends to thin out toward the end of each obligation year, so apply early rather than late.

What About GBIS Specifically?

The Great British Insulation Scheme is the most accessible of the three programmes because it does not require you to be on benefits. However, GBIS is limited to a single insulation measure—typically loft or cavity wall insulation. Window replacement is not currently covered as a standalone measure under GBIS.

The value of GBIS lies in establishing a baseline of energy efficiency. If your home has no loft insulation and an EPC of E, completing a GBIS-funded loft installation can lift the rating to D, potentially making the property eligible for further ECO4 funding that does cover windows.

What most guides miss: The “TrustMark” Gatekeeper

The most common reason grant applications fail isn’t the homeowner’s eligibility—it’s the installer.

To claim funding from ECO4 or GBIS, you must use a TrustMark-registered installer. If you hire a “local handyman” and then try to claim the cost back from the energy company, you will be rejected. The TrustMark registration ensures that the work meets the technical standards required for the government to count the carbon savings.

For those performing a deep retrofit, integrating grant-funded insulation with a high-performance glazing spec (see our Passivhaus windows spec) can practically eliminate your heating bill. If your home is currently Unmortgageable because of severe damp and inefficient glazing, these grants are the fastest way to restore the property’s value and mortgageability without spending your own capital.

Integration with Energy Autonomy

If you are combine grant-funded upgrades with a solar PV installation via IWantSolar, you are effectively moving your home toward a “Net Zero” operational cost. The grants handle the “leaks” (insulation and windows), and the solar handles the “gain.”

Summary: How to apply

1. Check your EPC: If you’re C or above, you’re unlikely to qualify for these specific grants.
2. Find a TrustMark Installer: Search the TrustMark directory for “Energy Efficiency” specialists.
3. Apply for ECO4 first: If you meet the low-income criteria, this is the most comprehensive funding.
4. Fall back to GBIS: If you are in an inefficient home but don’t meet the income thresholds.