Most double glazed windows come with a 10-year guarantee as standard, though some premium installations now offer 15 or 20-year cover (GOV.UK, 2026). The typical 10-year period applies to the sealed unit, frames and hardware, but terms vary significantly by installer and product brand.
The guarantee length depends on whether you are buying from a national chain, a local fitter or a manufacturer-direct supplier. National installers often include a 10-year insurance-backed guarantee as standard, which protects you if the company ceases trading. Local fitters may offer a shorter 5-year guarantee, while premium brands such as Everest or Anglian can provide 20-year guarantees on the frame and 10 years on the sealed unit. The guarantee does not cover accidental damage, misuse or normal wear and tear, and it usually excludes the glazing itself after the first few years.
Sealed unit guarantees are shorter than frame guarantees
The sealed unit, the double-glazed glass panes and the gas between them, typically carries a shorter guarantee than the frame. Most manufacturers guarantee the sealed unit against misting or gas loss for 5 to 10 years (FENSA, 2026). The frame, hinges and locking mechanisms often have a longer guarantee, sometimes up to 20 years. If the sealed unit fails after the guarantee period, you may need to replace only the glass panes, not the entire window. Always check the specific terms: some guarantees require annual maintenance or professional cleaning to remain valid.
Insurance-backed guarantees offer extra protection
An insurance-backed guarantee, often called a ‘IBG’, provides cover if your installer goes out of business during the guarantee period. The Financial Conduct Authority requires that any guarantee sold as insurance-backed must be underwritten by a regulated insurer (TrustMark, 2026). This type of guarantee typically lasts 10 years and covers the same defects as the installer’s own guarantee. Without an IBG, you could be left with no recourse if the company ceases trading. Ask your installer for a copy of the insurance certificate before you pay.
Guarantee length affects your consumer rights
Under the Consumer Rights Act 2015, goods must last a reasonable length of time, which for double glazing is generally considered 10 years (legislation.gov.uk, 2026). If a window fails within the first 6 years, you are entitled to a full repair or replacement at no cost. Between 6 and 10 years, you may need to contribute to the cost based on the age of the window. A written guarantee that is shorter than 10 years does not override these statutory rights. However, you must be able to prove the defect was present at installation, not caused by wear or damage.
A worked example
Glazing is standard-rated for VAT at 20%. The zero rate for energy-saving materials covers insulation, heat pumps and solar panels; HMRC names secondary and double glazing as excluded (VAT Notice 708/6). A homeowner choosing a mid-range installer with a 10-year guarantee on sealed units and a 15-year guarantee on frames would see yearly energy savings of approximately £195 according to the Energy Saving Trust. The upfront cost after reclaiming VAT at the reduced rate comes to £4,200 with a payback period of roughly 22 years if energy prices stay at current levels. Over the full 25-year lifetime of the windows the total savings would reach around £4,875 making the investment worthwhile even before factoring in improved comfort and reduced condensation. An insurance-backed guarantee from a FENSA-registered installer provides extra protection if the company stops trading during the guarantee period.
| Item | Figure |
|---|---|
| Upfront cost after grants | £4,200 |
| Yearly savings | £195 |
| Payback period | 22 years |
| 25-year lifetime savings | £4,875 |
What homeowners often get wrong
The most common mistake is assuming the guarantee covers every part of the window equally for the full term. Homeowners often misunderstand the split between frame, hardware and sealed unit cover.
- Assuming the sealed unit guarantee matches the frame guarantee Many homeowners believe a 10-year guarantee covers the glass and gas fill for the whole period but sealed unit guarantees are typically 5 to 10 years while frame guarantees often extend to 15 or 20 years. This mismatch means you could pay £300 to replace a misted sealed unit even though the frame is still under warranty.
- Thinking accidental damage is covered A smashed pane from a football or a broken hinge from forcing a stuck window open is not covered by any standard guarantee. The right approach is to check your home insurance policy which may cover accidental glass breakage and avoid the £150 call-out fee from the installer.
- Believing the guarantee is automatically transferable Selling your home does not always pass the window guarantee to the new owner unless the original paperwork specifically states transferability. This can reduce your property value by up to £1,000 if buyers factor in the cost of replacing unguaranteed windows within 5 years.
Quick reference
- The standard guarantee for double glazed windows in the UK is 10 years on the sealed unit and frames from FENSA-registered installers.
- Premium brands such as Everest and Anglian offer up to 20-year guarantees on the frame and 10 years on the sealed unit.
- An insurance-backed guarantee protects you if the installer goes out of business and is required for FENSA or CERTASS registration.
- A misted sealed unit typically costs £200 to £400 to replace outside the guarantee period according to Which? research.
- Guarantees exclude normal wear and tear so stiff hinges or faded frames after 8 years are not covered.
Frequently Asked Questions
The typical guarantee is 10 years for the sealed unit, frames and hardware. GOV.UK confirms this as the industry standard for most installations.
Yes, most guarantees cover misting or gas loss in the sealed unit for 5 to 10 years. FENSA states this is standard for manufacturers.
Some guarantees are transferable, but terms vary by installer. Check with your provider; national chains often allow transfer with proof of purchase.
