How to Choose a Window Installer

Checking accreditation

Installers working with windows and doors should hold a recognised competent person scheme accreditation, most commonly CERTASS or FENSA, which allow them to self-certify that replacement windows and doors comply with building regulations without needing a separate council building control inspection for each job.

Accreditation isn't just a badge; it means the installer's work is periodically audited and that a formal complaints and compliance process exists if something goes wrong. Ask to see the accreditation certificate or check the relevant scheme's online register before committing to a quote.

Insurance-backed guarantees

A standard installer's guarantee is only as good as the company that issued it; if the business closes down, the guarantee usually becomes worthless. An insurance-backed guarantee is underwritten separately, so if the original installer stops trading, the remaining guarantee period is still honoured through the insurance policy.

A 10-year insurance-backed guarantee is a reasonable expectation for windows and doors, and it's worth asking specifically whether the guarantee offered is insurance-backed or simply a company promise, since the two are not the same thing.

Who actually fits the work

Some companies sell and survey the job themselves but subcontract the actual fitting to third parties, whose standard and consistency can vary from job to job. Others, employ their own fitters directly, which generally means more consistent quality control and clearer accountability if a fitting issue needs resolving after the event.

It's a fair question to ask any installer directly: will the people fitting my windows be your own employees, or subcontracted?

Written quotes and spec detail

A proper written quote should specify far more than just a total price. It should set out the frame material and profile, glazing specification including glass thickness and any coatings, hardware including lock and handle type, colour and finish, and any structural work such as lintels, cills or making good to brickwork and plaster.

A vague one-line quote with a single price and no specification detail makes it very difficult to compare against another quote fairly, and leaves room for disagreement later about what was actually agreed.

• Frame material, profile and colour
• Glazing specification and glass type
• Hardware: locks, handles, hinges
• Any structural or making-good work included
• Payment schedule and guarantee terms

Deposits and payment staging

It's normal for installers to ask for a deposit to order made-to-measure frames, since these can't be resold if a customer cancels. What's worth checking is the size of that deposit relative to the total job value, and whether the remaining balance is staged, for example on delivery and on completion, or asked for entirely upfront.

Be cautious of requests for full payment before any work has started, or deposits that seem unusually large relative to the size of the job.

High-pressure sales tactics

Some sales approaches use time-limited discounts, on-the-spot signing requirements, or reluctance to leave a written quote for you to consider, all of which are worth treating as a warning sign rather than a genuine bargain. A reasonable installer will provide a free written quote and be comfortable with you taking time to compare it against others.

If a salesperson insists you must decide within the visit to get a particular price, that pressure itself is a reason to pause and think rather than sign.

Warranty paperwork and building regulations certificates

Once work is complete, you should receive a FENSA or CERTASS compliance certificate confirming the installation meets building regulations, along with the guarantee documentation and any product warranties from the manufacturer. Keep these together, since they're relevant to home insurance, and to any future sale of the property, as buyers' solicitors commonly ask for building regulations evidence for replacement windows and doors.

Questions worth asking before you commit

A short list of direct questions can clarify a lot before you sign anything. Asking these plainly, and expecting clear answers, is a reasonable part of getting a free quote from any installer.

• Are you CERTASS or FENSA accredited, and can I check that online?
• Is the guarantee insurance-backed, and for how many years?
• Will your own fitters do the work, or is it subcontracted?
• What deposit is required and how is the balance staged?
• Will I receive a building regulations compliance certificate on completion?

Common questions

What's the difference between CERTASS and FENSA?

Both are competent person schemes allowing installers to self-certify building regulations compliance for windows and doors. They operate similarly; the practical difference for a homeowner is mainly which scheme a particular installer belongs to.

Why does it matter if the guarantee is insurance-backed?

A standard company guarantee stops being of any use if that company closes down. An insurance-backed guarantee is underwritten separately, so cover continues even if the original installer is no longer trading.

Is it normal to pay a deposit before work starts?

Yes, since windows and doors are made to measure and can't easily be resold. What matters is that the deposit is reasonable relative to the job value and the remaining balance is staged sensibly.

Should I get more than one quote?

Comparing two or three written quotes with full specification detail is a sensible way to check that pricing and product specification are both reasonable before committing.