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 judging which firm does it best for the money. This guide covers the like-for-like checklist, 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 and another quotes A++, or one includes making-good and another leaves you to replaster, the numbers are not comparable and the 'cheapest' quote may be the worst value. Comparing like-for-like is the whole point: 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.
- 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 (A, A+ or A++) and the gas fill, because these change both price and performance.
- Hardware. Handles, locks and hinges to the same standard across quotes.
- Trickle vents. Whether they are fitted, since Building Regulations often require them on replacement windows.
- Making-good and plastering. Whether the firm repairs the reveals and finish after fitting, or leaves that to you.
Nine times out of ten, the quote that looks cheapest is not doing the same job. I have seen firms drop the glass rating, skip the trickle vents or leave the plastering out, and the customer only spots it when the fitters have gone. Get every line matched before you look at the total.
Tom Bradley, FENSA-registered installer
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.
| 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 |
| 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 | Confirms how long you are covered and whether it survives the firm closing |
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. 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.
- 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
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, the trickle vents, the making-good and the guarantee on each before you compare the bottom line. If one number stands out, work out exactly why before you either reject it or accept it. If you want a sense check, the quote quality auditor flags 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, 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, is the sweet spot.
A written specification listing every window, its dimensions, frame colour and finish, glass spec (A, A+ or A++ and the gas fill), hardware and trickle vents, plus whether making-good and plastering are included. It should also show the firm's FENSA or CERTASS registration, the deposit terms, the guarantee length, and whether an Insurance-Backed Guarantee is included.
Compare like-for-like or the comparison is meaningless. Match the unit count, dimensions, frame colour and finish, glass spec and gas fill, hardware, trickle vents and whether making-good is included across all three quotes. 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. Before you accept the cheap quote, check exactly what it 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, 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.