There is no single “best” double glazing company that works for every UK home, but the most reliable choice is a local or national installer registered with FENSA or TrustMark, as these bodies ensure compliance with Building Regulations. The government’s TrustMark scheme reports that over 1.3 million homes have used its registered installers since 2022 (TrustMark, 2026).
The right company depends on your home’s window style, budget, and location. National chains offer standardised products and warranties, while local firms often provide more personalised service and quicker installation. Your choice also hinges on whether you want uPVC, aluminium, or timber frames, and whether you need specific energy ratings or security features. Always verify installer credentials before committing.
Check FENSA or TrustMark registration first
Any double glazing company you consider must be registered with FENSA (Fenestration Self-Assessment Scheme) or TrustMark to legally install windows under Building Regulations. FENSA-registered installers cover over 90% of replacement window work in England and Wales (FENSA, 2026). Without this registration, you may need separate building control approval, which costs around £200–£400 per installation. A FENSA certificate also protects you if you sell your home within 10 years, as it proves compliance.
Compare quotes from at least three companies
Prices for double glazing vary significantly. The Energy Saving Trust states that a typical double-glazed window costs between £400 and £1,200 installed, depending on size and frame material (Energy Saving Trust, 2026). National chains like Everest or Anglian often charge premiums for brand reputation, while local firms may undercut by 20–30%. Always request itemised quotes detailing glass type (double or triple), frame material, and warranty length. A 10-year guarantee is standard, but some companies offer 15–20 years.
Prioritise energy ratings and security standards
Look for windows with a Window Energy Rating (WER) of A+ or higher, which reduces heat loss by up to 30% compared to old single glazing. The British Fenestration Rating Council (BFRC) certifies these ratings (BRE, 2026). Also check for PAS 24:2016 security certification, which ensures locks and frames resist forced entry. Companies like Safestyle and Everest often meet this standard as standard. Avoid any company that cannot provide third-party certification for either energy or security.
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). With a FENSA-registered local installer using A-rated double glazing, Energy Saving Trust estimates annual heating bill savings of roughly £195 for a gas-heated home. The payback period sits at about 33 years, meaning the financial return comes from added property value and comfort rather than energy savings alone. Over 25 years, total savings on energy bills reach approximately £4,875, but the real benefit lies in reduced draughts and condensation. For those on certain benefits, the ECO4 scheme may partially cover costs, though double glazing is not a primary ECO4 measure. Always check the Energy Saving Trust for region-specific figures before comparing quotes.
| Item | Figure |
|---|---|
| Upfront cost after grants | £6,500 |
| Yearly savings | £195 |
| Payback period | 33 years |
| 25-year lifetime savings | £4,875 |
What homeowners often get wrong
The most common mistake is choosing a company based on the lowest quote without checking FENSA or TrustMark registration. This leads to three key errors that cost homeowners time and money.
- Skipping FENSA checks before signing An unregistered installer cannot self-certify your windows, meaning you must pay £200–£400 for separate building control approval. This often wipes out any savings from the cheap quote.
- Assuming all A-rated windows are equal The energy rating only tells part of the story, look at the whole-window U-value (target below 1.4 W/m²K) and the BFRC rating. A poor seal or thin frame can halve the real-world performance, wasting up to £100 a year in lost heat.
- Ignoring the warranty small print Many national chains offer a 10-year guarantee, but it often excludes labour after year one or requires annual maintenance you never signed up for. This can leave you paying £300–£500 for a simple seal replacement within five years.
Quick reference
- FENSA-registered installers cover over 90% of replacement window work in England and Wales. That makes it the first credential to check.
- An A-rated double glazed window typically has a U-value between 1.2 and 1.4 W/m²K, which is three times better than a single-glazed equivalent.
- You do not need planning permission for like-for-like replacement windows unless your home is listed or in a conservation area.
- Payback on double glazing through energy savings alone is rarely under 20 years, but the comfort improvement and reduced condensation are immediate benefits.
- Avoid companies that demand a full payment upfront, reputable installers ask for a deposit of 10–25% and the balance on completion.
Frequently Asked Questions
The best double glazing company depends on your home and budget. TrustMark reports over 1.3 million homes have used its registered installers since 2022 (TrustMark, 2026).
Yes, you need a FENSA or TrustMark registered company to legally install windows under Building Regulations. FENSA-registered installers cover over 90% of replacement window work in England and Wales (FENSA, 2026).
Prices vary significantly, but the Energy Saving Trust states that a typical double-glazed installation costs between £3,000 and £7,500 for an average three-bedroom home. Getting quotes from at least three companies helps you find the best deal.
