Replacing windows and doors is one of the more significant home improvement decisions you will make. Get it right and you can enjoy better insulation, lower energy bills, improved security, and a home that looks noticeably smarter. Get it wrong and you could be dealing with draughty frames, failed seals, or a supplier who disappears the moment something goes wrong.
The market is crowded, and not every company offering to upgrade your glazing is worth your time or your money. Asking the right questions before signing anything can save you considerable stress further down the line.
Are they a FENSA or CERTASS registered installer?
In England and Wales, replacement windows and doors must comply with building regulations. A competent person scheme like FENSA or CERTASS allows registered installers to self-certify that their work meets those standards, meaning you will not need to apply for building regulations approval separately.
Any reputable installer should be registered with one of these schemes. If they cannot confirm this upfront, that is a warning sign worth paying attention to.
What materials and finishes do they offer?
Not all frames are created equal. uPVC remains the most popular choice for its low maintenance and affordability, but aluminium and timber frames each have their own advantages depending on your home’s style and your long-term priorities. Aluminium, for instance, offers slimmer sightlines and a more contemporary appearance, while timber suits period properties and can be more sympathetically repaired over time.
Finishes matter too. If you want something beyond white uPVC, ask what customisation is available. Some suppliers offer a full colour coating service, which can dramatically transform the look of existing or new frames without requiring full replacement, opening up a much wider range of aesthetic options.
What energy ratings do their products carry?
Window Energy Ratings (WERs) run from A++ down to E. A-rated windows and above are generally considered energy efficient and will make a meaningful difference to heat retention in your home. Ask specifically what rating the products they are recommending carry, and get this in writing rather than accepting a vague assurance that they are “energy efficient.”
For doors, look for a low U-value, which measures how readily heat passes through the material. The lower the number, the better the thermal performance.
What does the guarantee actually cover?
Most reputable window and door companies offer guarantees of ten years or more on their products and installation. But the small print matters enormously. Some guarantees cover the frames but not the sealed units. Others exclude damage caused by certain weather conditions or maintenance failures.
Ask exactly what is and is not covered, how long the guarantee lasts, and importantly, what happens to your guarantee if the company ceases to trade. Some installers are backed by an insurance-backed guarantee scheme, which offers protection even in that scenario.
Can they provide references or show you completed work?
Any company with a solid track record should be happy to point you toward reviews, testimonials, or examples of previous installations. Look beyond the testimonials on their own website and check independent platforms such as Trustpilot, Google Reviews, or Checkatrade.
If the job is particularly large or involves a heritage property with planning considerations, asking to speak with a previous customer is entirely reasonable. A company confident in its work will welcome that request.
What is included in the quote, and when will the work be done?
A detailed written quote should break down the cost of each element: supply, installation, removal and disposal of old frames, any making-good of surrounding plaster or brickwork, and VAT. If a quote is vague or presented as a single figure without breakdown, ask for more detail.
You should also ask for a realistic installation timeline. Lead times for certain frame materials or bespoke sizes can stretch to several weeks, so if you are working to a deadline, confirm this early.
Will the installer manage planning or permitted development considerations?
Most window and door replacements fall under permitted development and do not require planning permission, provided the new units match the appearance of the originals in terms of material and colour. However, if you live in a listed building, a conservation area, or a property with specific planning conditions, restrictions may apply.
A knowledgeable installer should be able to advise you on this and flag any constraints before work begins, rather than leaving you to discover a planning issue after the fact.
Taking time to ask these questions before committing to any supplier will give you a much clearer picture of who you are dealing with and what you can expect. The cheapest quote rarely accounts for all the factors that make a job genuinely good value, and with windows and doors lasting twenty years or more, the decision is worth getting right from the outset.
