Getting three quotes is the standard advice for double glazing, and it is good advice, but only if you compare them properly. Three prices for three subtly different jobs tell you nothing. The skill is making every quote describe the same work, then reducing each one to a single comparable number: the cost per window. This guide covers the like-for-like checklist, the arithmetic that turns three totals into three comparable figures, what every written quote must contain, and the red flags that should stop you signing. Before the salespeople arrive, price the job yourself in the uPVC window calculator so you walk into every visit already knowing a fair figure.
Why three quotes only work like-for-like
Three quotes exist to give you a market rate and to expose the firm that is over the odds or suspiciously cheap. That only works if each quote describes an identical job. If one firm quotes A-rated glass at about 1.2 to 1.4 W/m²K and another quotes A++ at 0.8 to 1.0, the second is almost certainly a triple-glazed job carrying a 10 to 20% cost premium, and the two totals were never comparable. The same goes for making-good: one quote includes replastering the reveals and the other leaves it to you, and the 'cheapest' quote may be the worst value. Match the specification first, then let the prices speak. It is also the single most effective way to avoid overpaying for double glazing, because it removes the salesperson's room to hide a downgrade behind a lower number.
The like-for-like checklist
Before you can compare prices, pin down the job. Ask every firm to quote against the same list so nothing drifts between visits:
- Unit count and dimensions. The same number of windows, at the same sizes, in each quote. A flat typically has 4 windows, a mid-terrace 8 to 10, a semi 10 to 12 and a detached 12 to 16. If two quotes count differently, one of them has missed an opening or bundled two into one.
- Frame material. Fully fitted, uPVC runs £400 to £1,000 per window, aluminium £550 to £1,300 and timber £900 to £2,000. Aluminium carries a 30 to 40% premium over uPVC and timber 60 to 110%, so a quiet material swap on one quote can move the total by more than any negotiation will.
- Frame colour and finish. White, a woodgrain foil or a colour, and matched inside and out if that matters to you.
- Glass specification. The energy rating, the U-value figure and the gas fill, set out in the table below, because these change both price and performance.
- Hardware. Handles, locks and hinges to the same standard across quotes.
- Trickle vents. Since the 15 June 2022 update to Approved Document F, most replacement windows must be fitted with them, and Table 2 of that document sets the background ventilator equivalent area at about 8,000 mm² for a habitable room and 4,000 mm² for a wet room. A quote that leaves them off is quoting a different, cheaper job.
- Making-good and plastering. Whether the firm repairs the reveals and finish after fitting, or leaves that to you.
- Removal and disposal. A fully fitted price should take the old frames away; confirm it is written in rather than added later.
| Glass line in the quote | What it should state | What it does to the price |
|---|---|---|
| Energy rating | A, A+ or A++ on the BFRC scale. Band A is the sensible standard, at an Energy Index of 0 or above | Moving up to band A from a lower band is roughly £0 to £50 per window |
| U-value | A figure in W/m²K, not just a letter. A-rated is about 1.2 to 1.4, A+ about 1.2, A++ as low as 0.8 to 1.0 | Part L has required 1.4 W/m²K or WER band B on replacement windows since 15 June 2023, so an A-rated unit clears the floor |
| Gas fill | Argon is the standard fill and performs best in a 12 to 16 mm cavity; krypton belongs in the narrow 9 to 12 mm cavities of triple and slim units | A+ or A++ generally means stepping up to triple glazing, a 10 to 20% cost premium |
Band A is the baseline rather than a premium feature: most quality modern double glazing reaches it as standard.
The quote that looks cheapest is often not doing the same job. Drop the glass from A++ to A, leave the trickle vents off, price the plastering out, and the total falls without a single line saying so. Get every line matched before you look at the total, then divide by the window count.
Double Glazing Cost Calculator Team
Working out the cost per window
The most useful sum you can do with three quotes is the simplest one: the quoted total divided by the number of windows in the specification. It strips out house size, which is the biggest single reason two honest quotes differ, and leaves you with one number you can test against a published range. The ranges below are the same ones behind our double glazing costs research, all fully fitted.
| Material | Per window, fitted | Lifespan | Best for |
|---|---|---|---|
| uPVC | £400-£1,000 | 20-25 yrs | Most modern UK homes; best value |
| Aluminium | £550-£1,300 | 30-40 yrs | Slim modern frames, large openings |
| Timber | £900-£2,000 | 30-60 yrs | Period and conservation-area homes |
Divide each quoted total by the window count and test the answer against the row for the material you specified.
Work a real example. A semi-detached of 10 to 12 windows sits at £5,000 to £12,000 fully fitted in uPVC, averaging £8,000. Divide the average across 10 windows and you get £800 each; across 12 you get £667. Both sit inside the £400 to £1,000 uPVC band, so the quote is unremarkable. Now take the £12,000 top of that range: over 12 windows it is exactly £1,000 a window, the ceiling of the band, and over 10 it is £1,200, above it. That does not prove overcharging. It tells you the quote is not a plain uPVC casement job, and that the extra should be traceable to a line in the spec: a bay, a sash, an aluminium frame, a triple-glazed upgrade. If nobody can point at that line, you have found your question.
| House type | Typical windows | Low | Average | High |
|---|---|---|---|---|
| Flat | 4 | £1,800 | £3,200 | £5,000 |
| Bungalow | 8 | £3,500 | £5,500 | £8,000 |
| Mid-terrace / 3-bed | 8-10 | £4,000 | £6,500 | £10,000 |
| Semi-detached | 10-12 | £5,000 | £8,000 | £12,000 |
| Detached | 12-16 | £7,000 | £11,000 | £16,500 |
Source: DGCC 2026 dataset. The highlighted semi-detached row is the worked example above.
How to judge the spread between the three quotes
Three quotes on the same job rarely land on the same number, and the obvious question is how wide a gap is normal. Read each quote against the published range for the material and style rather than against the other two, because a spread of three can be wide for an honest reason (one firm has quoted a bay you forgot to mention) or narrow for a bad one (all three have quietly left out the making-good).
One explanation you can rule out straight away is location. Prices do vary by region, by +20% in London and -13% in Wales against the UK average on our own multipliers, but all three of your quotes are for the same house in the same postcode, so geography cannot account for a gap between them. Everything left has to be explained by a line in the specification.
What every written quote must contain
A price on its own is not a quote. Insist that each firm puts the job in writing, with enough detail that you could hold them to it. A proper written quote protects you if the finished work does not match what you agreed, and it is the document the quote quality auditor checks against, one of the decision tools built for exactly this stage of the job.
| What the quote must show | Why it matters |
|---|---|
| Written specification | So you can compare like-for-like and hold the firm to the agreed job |
| Unit count and dimensions per opening | Without a count you cannot do the total-divided-by-windows sum that makes three quotes comparable |
| Glass spec with a U-value | A replacement window must reach 1.4 W/m²K or WER band B under Part L, in force since 15 June 2023 |
| Trickle vents | Required on most replacement windows since the 15 June 2022 Approved Document F update, at about 8,000 mm² equivalent area for a habitable room |
| Making-good, plastering and disposal | The three lines most often left out of a low quote, and the ones you pay for separately if they are |
| FENSA or CERTASS registration | Proves the fitter can self-certify the work under Building Regulations |
| Deposit terms | A modest deposit is normal; a large one puts your money at risk |
| Guarantee length + IBG | 10 years is common on frames and 15 from some installers, against about 5 years on the sealed units; the IBG confirms the cover survives the firm closing |
| Lead time and fitting time | Expect 3 to 6 weeks from quote to fitting day, most of it manufacture, then 1 to 2 days on site for a standard house |
An Insurance-Backed Guarantee (IBG) keeps the workmanship guarantee valid even if the installer stops trading.
The FENSA or CERTASS registration is worth confirming for its own sake, not just as a box to tick. Our guide to what FENSA means explains why the certificate matters when you eventually sell the house, and why an unregistered fitter leaves you to arrange Building Control approval yourself.
Red flags that should stop you signing
Some warning signs are worth walking away from no matter how appealing the price. Treat all of these as a reason to pause:
- No written scope or specification. If a firm will not put the job in writing, you have nothing to compare and nothing to enforce.
- A price far below the others. Run the per-window sum on it first. A supply-only uPVC casement starts at around £160, and the gap between supply-only and fully fitted is £200 to £600 per window, so a 'fitted' price much under £400 a window has almost no fitting in it. A big gap under the other quotes nearly always hides a spec downgrade, not a better deal.
- A large upfront deposit. A big share of the total demanded before any work starts puts your money at risk, and the materials it supposedly funds take only 3 to 6 weeks to arrive.
- Pressure to sign the same day. A genuine quote is still valid next week; a today-only price is a sales tactic.
How to line the three quotes up
Getting to three is the hard part, and you do not have to chase them yourself: you can get double glazing quotes from installers covering your area in one go.
Once you have three written quotes built on the same specification, put them side by side and read them line by line rather than skipping to the totals. Check the glass rating and its U-value, the trickle vents, the making-good and the guarantee on each, then divide every total by the window count and write the three per-window figures at the top of the page. If one number stands out against the £400 to £1,000 uPVC band, work out exactly which line explains it before you either reject it or accept it. If you want a sense check, the quote quality auditor and the rest of our decision tools flag what a quote has left out, and the cheapest double glazing guide explains which levers genuinely cut the price rather than the spec. Three matched quotes, read carefully and reduced to a cost per window, are the best protection you have.
Frequently asked questions
At least three. Three quotes give you a fair sense of the market rate and make it obvious when one firm is high or low. Fewer than three and you have nothing to sanity-check a price against; many more and the visits become a chore without adding much. Three, compared like-for-like and each divided down to a cost per window, is the sweet spot.
Divide the quoted total by the number of windows in the specification. Fully fitted in uPVC, that figure should land between £400 and £1,000 per window, around £650 on average; aluminium runs £550 to £1,300 and timber £900 to £2,000. So a semi-detached with 10 to 12 windows quoted at £8,000 works out at £667 to £800 a window, comfortably inside the uPVC band. If the result sits outside the band for the material, find out which line explains it before you judge the quote.
A written specification listing every window, its dimensions, frame colour and finish, glass spec (A, A+ or A++, the U-value in W/m²K and the gas fill), hardware and trickle vents, plus whether making-good, plastering and removal of the old frames are included. It should also show the firm's FENSA or CERTASS registration, the deposit terms, the guarantee length (10 years is common on frames, about 5 years on the sealed units) and whether an Insurance-Backed Guarantee is included.
Compare like-for-like or the comparison is meaningless. Match the unit count, dimensions, frame material, colour and finish, glass spec and gas fill, hardware, trickle vents and whether making-good is included across all three quotes. Then divide each total by the window count and test the result against the range for that material, £400 to £1,000 a window in uPVC. Only once every quote describes the same job can you judge which firm is genuinely cheaper.
A price far below the other quotes usually hides a spec downgrade rather than a better deal. It might be a lower-rated glass unit, no trickle vents, no making-good, or a shorter guarantee. The arithmetic gives you a floor: a supply-only uPVC casement starts at around £160 and the gap between supply-only and fully fitted runs £200 to £600 per window, so a fitted price much below £400 a window has very little fitting in it. Check exactly what the cheap quote includes against the others, because the gap is nearly always explained by something left out.
A large upfront deposit is a red flag. A reputable installer may ask for a modest deposit to order materials, which typically take 3 to 6 weeks to manufacture, but a demand for a big share of the total before any work starts puts your money at risk if the firm runs into trouble. Be cautious, and check the deposit terms are in writing.
No. Pressure to sign the same day is one of the clearest warning signs in this trade. A genuine quote is still valid next week, so take your time, compare all three like-for-like, and never let a today-only discount rush the decision.