Questions to ask a double glazing installer
The right questions turn a sales visit into a genuine comparison. Asking the same things of every installer gives you answers you can line up side by side, and it quickly separates a solid firm from a risky one. Use the questions below as a calm checklist — there is no need to memorise them, and a good installer will welcome every one.
About the company
- How long have you been trading, and are you a limited company?
- Are you registered with FENSA or CERTASS so the work is self-certified?
- Can I see recent local jobs or independent reviews?
- Will your own team carry out the fit, or is it subcontracted?
Accreditation is fundamental here, so it is worth reading our guide to FENSA, CERTASS and the GGF before you ask. It also helps to read how to vet an installer first so you know how to check the answers you are given.
About the product and specification
- What frame material, glass and hardware are you quoting for?
- What is the energy rating or U-value of the windows?
- Is the price for the exact specification I asked for?
- What colours, finishes and glazing options are included?
To ask these with confidence, it helps to compare glazing types before you compare firms and to see materials ranked and reviewed. Our guide to reading a spec sheet explains what the answers should look like on paper.
Want installers worth asking? We match you with vetted double glazing firms so you can put the same questions to each — free and with no obligation.
About the guarantee
- How long is the workmanship guarantee, and what does it cover?
- Is it backed by an insurance-backed guarantee if you cease trading?
- Is the guarantee transferable if I sell the house?
An insurance-backed guarantee is one of the most valuable answers you can get, so read our guide to insurance-backed guarantees to understand why.
About money and timing
- What deposit is required, and is it protected?
- How are the remaining payments staged?
- What is the lead time, and how long will the installation take?
- What happens if the survey reveals extra work?
Our guide to deposits and payment terms explains what is normal, and if any answer feels like pressure, our list of quote red flags will help you keep your bearings.
After the visit
Once every installer has been, gather the written answers and quotes in one place and compare them line by line. Look for consistency between what was said on the day and what appears on paper — a firm whose written quote matches its verbal promises is usually a firm you can trust. If an answer was vague or an installer dodged a question, that tells you something too. Give yourself a day or two to reflect rather than deciding on the spot; the strongest choice is rarely the one made under pressure.
Ask the same questions of everyone, write the answers down, and compare them alongside the quotes. Requesting and comparing quotes is free and no-obligation, and comparing while installers still have Q3 fitting slots in your area keeps your dates open while you weigh things up. If you would like to walk through the quote process step by step, that is a useful primer before any visit.