The short version
- Get three written quotes for exactly the same windows and spec. Citizens Advice recommends quotes from at least 3 traders.
- Check every quote for the glass rating, a competent person scheme such as FENSA or CERTASS, and an insurance-backed guarantee.
- FENSA is not a guarantee. The guarantee comes from the installer.
- Get every installer to list what the quote leaves out, in writing.
- Never sign on the day. Take the written quotes away and compare them first.
1. Ask every installer to quote the same job
Comparing double glazing quotes only works when every installer prices the same job. One installer prices standard double glazing, another adds triple glazing and a new front door, and a third leaves out the bay. The totals then tell you nothing.
Write down what you want quoted before anyone visits:
- How many windows, and which panes open
- Frame material and colour, for example white uPVC, anthracite grey aluminium or painted timber
- Glass type: double or triple, plus obscure glass for bathrooms
- Extras priced as separate lines, such as doors, trickle vents or new sills
Give the same list to every installer. Ask for any suggested upgrade as a separate line, so the base quote still compares like for like. In a flat, the list starts from the freeholder's or the council's written spec. In Norwich, where 35.9% of households live in flats, our page on Norwich double glazing tells you to give that spec to every installer.
Ask what each quote leaves out
Ask every installer to list in writing what its quote excludes. Two quotes that look alike can differ on these five items:
- Making good inside and out after the old frames come out
- Disposal of the old frames and glass
- Access equipment, such as scaffolding for upper floors
- Internal window sills
- Trickle vents
Put the list on the written quote, next to the price. Step 6 explains why written answers count.
2. Work out the price per window
Divide each quote's total by the number of windows, then compare that figure alongside what each quote includes. The per-window figure shows which quote is out of line. The contents of the quote show why.
| Example | What it lists | What to ask |
|---|---|---|
| Quote A, lowest per window | "Double glazed units" with no rating, no mention of removing the old frames, a guarantee with no insurance named | Which glass is it? Is removal included? Is the guarantee insurance-backed? |
| Quote B, middle | Glass U-value in writing, FENSA registration, removal and making good, a ten-year insurance-backed guarantee | When does the price stop being valid? Who fits the windows? |
| Quote C, highest per window | A large "discount if you sign today" against a list price | What is the price without the discount, in writing, and how long is it valid? |
A low quote that leaves things out is not cheaper once you add them back. A high quote with a same-day discount is a sales tactic, not a saving. For typical prices, our sister site explains what each double glazed window costs.
Get quotes that compare like for like
Tell us about your home and we pass your enquiry to local installers who cover your postcode.
3. Check the glass rating
Replacement windows in England must reach a U-value of 1.4 W/m²K or better, or a Window Energy Rating of band B or better. That standard sits in Approved Document L, Table 4.2, and has applied in full since 15 June 2023. A lower U-value means less heat lost through the window. In Leicester only 42.8% of homes with an EPC reach band C, which is why our page on double glazing quotes in Leicester compares quotes on energy as well as price.
Every quote names the glass in writing. A quote that only says "double glazed units" leaves you unable to compare it, so ask for the U-value or the energy rating. Compare U-value with U-value and WER band with WER band, because a quote can state either figure. Wales and Scotland set their own standards, so ask an installer there which one the windows meet. Our pages on double glazing in Swansea and Glasgow double glazing quotes set out the Welsh and Scottish rules.
4. Check the installer is registered
An installer registered with a competent person scheme signs the job off under Building Regulations and registers it for you. GOV.UK lists six schemes for replacement windows in existing homes: Blue Flame Certification, CERTASS, Certsure, FENSA, NAPIT and ASSURE. You then get a certificate, which your solicitor asks for when you sell.
An installer outside these schemes leaves you to apply to your council's building control yourself and pay its fee. Check each installer three ways:
- Ask which scheme they belong to, and get the answer on the quote.
- Search the installer's name on that scheme's website, for example the FENSA installer search at fensa.org.uk.
- Look the company up on Companies House to confirm it is active and how long it has traded. Our page on how to check a double glazing installer lists all nine checks to run.
FENSA and CERTASS self-certification applies in England and Wales. Scotland runs its own building standards system, so ask a Scottish installer how the work is approved.
5. Compare the guarantee and the deposit
Which? recommends a ten-year guarantee on the frames and a ten-year insurance-backed guarantee. A guarantee is only worth something while the installer is trading. An insurance-backed guarantee pays out if the installer stops trading. Check that every quote says which kind it offers.
Is FENSA a guarantee?
No. FENSA checks that the work meets Building Regulations and registers it with the council. The guarantee comes from your installer, and FENSA verifies that every FENSA Approved Installer's guarantee is insured. FENSA's complaints service does not handle guarantee claims.
Deposit protection and Section 75
Keep any deposit small and ask in writing whether it is protected. Some installers belong to schemes such as DGCOS, which offers deposit cover to members' customers. Paying at least part of the cost by credit card brings in Section 75 of the Consumer Credit Act 1974. Section 75 makes the card provider jointly liable with the installer for single items within the Act's price limits. Our guide on how much deposit to pay for double glazing covers deposit size and protection. The questions to ask a double glazing salesman cover both in detail.
6. Check what can change after the survey
A technical survey after you order takes the exact measurements, and some quotes allow the price to change at that point. Ask each installer in writing what the survey can change. Citizens Advice puts the difference plainly: "A quote is a fixed price", while an estimate "is just a rough guess, so you might end up paying more."
Ask four more things before you compare the final numbers:
- How long the quoted price is valid
- The expected start date, and what happens if the work runs late
- How bad-weather delays are handled
- Whether the fitters are employed by the company or subcontracted
Get the answers in writing. Under the Consumer Rights Act 2015, what a trader tells you about the service, and you rely on, becomes a term of the contract. Check the written contract against our double glazing contract checklist before you sign.
7. Don't sign on the day
A price that is "only valid today" is a sales tactic, not a discount. A fair installer gives you a written quote you can take time over.
If you sign at home, you usually have at least 14 days to cancel, but made-to-measure windows can be an exception, so check the contract before you sign. Our guide to the double glazing cooling off period sets out each case.
What should a double glazing quote include?
A double glazing quote includes every window and its specification, the glass rating, removal and making good, the scheme, the guarantee, the price with VAT, the deposit, the fitting date, the validity date and exclusions.
The Consumer Contracts Regulations 2013 require a contract signed at home to state the total price including taxes, the payment and performance arrangements, any deposit, and the guarantees. Print this table and fill in one column per quote:
| Item | Quote A | Quote B | Quote C |
|---|---|---|---|
| Every window, with its size, style and which panes open | |||
| Frame material, colour and hardware | |||
| Glass U-value or WER band | |||
| Removal and disposal of the old frames, and making good inside and out | |||
| Competent person scheme, such as FENSA or CERTASS | |||
| Guarantee length, and whether it is insurance-backed | |||
| Total price including VAT | |||
| Deposit amount and payment stages | |||
| Expected fitting date, and who carries out the fitting | |||
| Date the quote is valid until | |||
| What the quote excludes |
Compare quotes from local installers
The quickest way to get three quotes on the same specification is to ask several installers at once. Compare double glazing quotes from local installers who cover your postcode: the service is free and you are under no obligation. We are a free quote-matching service, not an installer.
Questions people ask
How many double glazing quotes should I get?
Get three written quotes for the same windows and specification. Citizens Advice recommends written quotes from at least 3 different traders before you decide. One quote gives you nothing to compare against.
Why are double glazing quotes so different?
Double glazing quotes differ mostly because they price different jobs: different glass, hardware, guarantees and extras. Line them up on the same specification first. The gap that remains reflects each firm's overheads and workload. Our page on double glazing in Chelmsford compares national firms and local fitters quoting for the same windows.
How to tell if double glazing is good quality?
Double glazing quality shows in four written checks: a glass U-value of 1.4 W/m²K or better (or WER band B), a competent person scheme, an insurance-backed guarantee, and named locks and handles. The U-value and WER figures are the England minimum in Approved Document L, so a quote that names neither gives you nothing to compare.
Can I get a quote for double-glazed windows online?
An online quote gives you a starting price, and the final price follows a technical survey that takes the exact measurements the windows are made to. Some installers adjust the price at that survey, so ask in writing what it can change.
Is the cheapest double glazing quote a bad sign?
The cheapest quote is a good deal when it lists the same specification, scheme registration and insurance-backed guarantee as the others. It is a bad sign when the low price comes from items left out.
