How to compare window quotes without comparing different things
Two proposals for 'the same window' are rarely the same window. What has to be written into every quote, and how to know you're actually comparing properly.
Why "identical" proposals rarely are
You asked for three quotes, all of them say "PVC window with double glazing", and the prices vary by several hundred euros between them. This does not mean one company is trying to cheat you, in most cases. It means the three of them are proposing different products, hidden behind the same generic description.
The difference usually sits in two details that rarely appear in a summary quote: the frame depth (measured in millimetres, invisible to the eye) and the glass makeup (thickness of each pane, gas in the cavity, spacer type). A 70 mm frame and an 82 mm frame both fit the phrase "PVC window": but they insulate quite differently, and cost quite differently.
Neither option is "wrong": a narrower frame can be perfectly adequate for a home with no major thermal demands, and it costs less. The problem isn't the difference itself. It's comparing a price without knowing that difference exists.
What every serious quote needs to include
A complete quote doesn't need to be complicated, but it does need to answer these points, if one of them is missing, ask for it before deciding based on that price.
- On-site measurement: The final figure has to come from an actual measurement, taken in your home, never an estimate over the phone or from photos. It is the single most common cause of a measuring error and a "surprise" once the quote is already agreed.
- Frame: brand, number of chambers and depth: A 70 mm profile and an 82 mm profile do not insulate the same way, even if the quote says "PVC frame" in both cases. Ask for the brand and the depth in millimetres, not just the colour.
- Glass: thickness, type and gas fill: The thickness of each pane, whether it is Low-E, acoustic or plain glass, and whether the cavity is filled with air or argon. Argon insulates better than air, but costs more, you need to know which one is actually in your quote.
- Spacer: aluminium or "warm edge": The metal bar between the two panes of glass also conducts cold. A "warm edge" spacer (composite, not metal) insulates better at the edges of the glass, a small detail, but one that separates a careful quote from a generic one.
- Uw value for the whole window: Not the glass value alone: the Uw of the assembled window, frame included. It is the one number that lets you genuinely compare insulation between two different proposals.
- Hardware: brand and number of lock points: One lock point and five are not the same product, even if the catalogue photo looks similar. If you asked for an RC2 security rating, it has to be written down, not just implied.
- Manufacturing and installation timelines, in writing: A timeline mentioned on the phone is worth nothing if it is not on paper. Ask for the delivery date and the expected installation time, with a reasonable range stated.
- Payment terms: The deposit amount, when the balance is due, and what happens if delivery is delayed. All of this should be written down before you sign, not agreed verbally.
- Warranty: duration and what it covers: How many years cover the frame, how many cover the glass, how many cover the installation, these are usually different periods, and a serious quote spells them out separately.
- VAT and what is included: Confirm whether the figure shown already includes VAT, and whether removing the old window and cleaning up the site are included or charged separately.
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Red flags before you sign
None of these signs on its own necessarily means bad faith, but the more of these that show up on the same quote, the more worth stopping to double-check before moving forward:
- The deposit requested is more than half the total value of the job.
- They agreed a price without coming to measure on site.
- The spec sheet is vague: "quality double glazing", with no thickness or frame brand stated.
- The price is noticeably lower than the other quotes, with no explanation for the difference.
- They are reluctant to give you contact details for past jobs or a verifiable address.
- Timelines are only spoken, never put in writing.
The deposit paid before work begins is the most commonly cited point when something goes wrong with a window installation, not because paying a deposit is a problem in itself, but because a disproportionate deposit leaves the customer with no leverage if the timeline or the quality doesn't hold up.
After signing: realistic timelines
Once the measurement is confirmed, manufacturing custom windows typically takes two to four weeks, special colours or non-standard frames can take longer, and a serious quote says so before you sign, not after the deadline has already passed. Installation itself is usually completed in a single day per home, with removal of the old frames included.
Always ask for the delivery timeline to be written into the quote or contract, with a reasonable range stated (e.g. "4-6 weeks" rather than one fixed date). A written timeline doesn't guarantee there will never be delays, but it gives you a concrete basis to raise it if a delay goes beyond what was agreed, which a promise made on the phone never does.
Frequently asked questions about comparing quotes
At least three, and they are only worth comparing if you ask for the same specifications in each, same frame depth, same glass type, same hardware brand (or a stated equivalent). Comparing a 70 mm frame with an 82 mm frame as if they were the same thing is the most common mistake, and the one that most distorts the decision.
Not necessarily, but it almost always means a different specification, a narrower frame, thinner glass, air instead of argon, single-point instead of multi-point hardware. Before deciding on price, confirm you are actually comparing the same window.
A deposit above half the total value before any work begins is a warning sign, not a normal practice in the trade. A smaller amount upfront, with the balance paid closer to delivery or after installation, is the safer standard for the customer.
You cannot tell by eye: the depth in millimetres and the number of chambers are the measurements that actually matter, and they come from the frame manufacturer's own spec sheet, not invented by the installer. Always ask for that number in writing.
Yes. A second opinion on a quote you already have costs you five minutes and can save you an expensive decision. We confirm whether the specification is complete and whether the price makes sense for what you are buying, even if you end up choosing another company.
If the timeline is written into the quote or the contract, you have a concrete basis to raise it, which is exactly why a written timeline is worth more than a date mentioned on the phone, even if it feels like unnecessary paperwork at the time.
Not automatically: some companies charge separately for removing and disposing of the old frames. Confirm this before signing, since it can be a real difference in final cost between two quotes that looked close at first glance.
No. A house on a quiet street does not need the same acoustic glass as a flat on a busy avenue, and an interior window does not need the same security class as a ground-floor door. Choosing for your actual situation saves money without giving up what actually matters to you.
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