Choosing a window and door installer is about more than comparing prices. The quality of the survey, product specification, installation and aftercare will all affect how well your new windows or doors perform.
Before signing a contract, ask who will complete the work, how Building Regulations compliance will be handled, what the quotation includes and which guarantees apply. You should also understand the proposed products, installation process and support available if something needs adjusting later.
A trustworthy installer should answer these questions clearly, without pressure or vague promises.
The Essential Questions To Ask Before You Commit
At a minimum, ask an installer about their experience, regulatory compliance, product recommendations, quotation, guarantees, installation team and aftercare.
The answers should help you establish:
- Whether the company understands your type of property
- Whether the proposed installation will meet relevant requirements
- Exactly what you are paying for
- Who is responsible at each stage
- What protection you have after installation
The following questions will help you compare window and door installers on more than price alone.
1. How Long Have You Been Installing Windows And Doors?
Experience does not guarantee perfect work, but it can show that an installer has dealt with different property styles, structural openings and installation challenges.
Ask how long the business has traded and whether it regularly completes projects similar to yours. Replacing a front door in a modern home may require a different approach from fitting sliding sash windows in an older property.
You can also check whether the company has a permanent business address, an established local presence and information about its history. Gallagher’s, for example, is a family-run business established in 2001. You can read more about the company’s background on the About page.
2. Are You Registered With A Competent Person Scheme?
Replacement windows and external doors may need to comply with Building Regulations. An installer registered with an authorised Competent Person Scheme can self-certify qualifying work instead of requiring a separate building control application.
Ask:
- Which scheme is the company registered with?
- Does the proposed work fall within that scheme’s scope?
- Will you receive a compliance certificate?
- Will the installation be registered with the local authority?
FENSA covers qualifying replacements of external windows, doors, roof windows and rooflights in homes. It does not cover every type of glazing project, so the installer should explain whether your work is eligible.
Gallagher’s has been a FENSA member since 2001. For qualifying work, the relevant certification is provided once the installation has been completed.
For further information, read the official GOV.UK guidance on using a Competent Person Scheme.
3. Do You Belong To A Recognised Industry Body?
Membership of a professional trade body is another useful trust signal, although it should be considered alongside experience, certification and the terms of the contract.
Ask what the membership involves and how it protects or benefits you as the customer.
The Glass and Glazing Federation represents businesses involved in manufacturing, supplying and installing glazing products. Its consumer guidance is designed to help homeowners understand products, specifications and installer selection.
Gallagher’s is a GGF member. This provides access to technical support, training, industry guidance and updates concerning regulations and thermal performance. The GGF also acts as Gallagher’s Alternative Dispute Resolution provider, offering access to an independent process if a complaint ever requires escalation.
Homeowners can also explore the Glass and Glazing Federation’s MyGlazing consumer guidance.
4. Who Will Survey And Install My Windows Or Doors?
The person who sells a product may not be the person who surveys or fits it.
Ask who will:
- Measure the openings
- Confirm the final specification
- Order the products
- Complete the installation
- Carry out any finishing work
- Handle post-installation queries
A detailed survey is essential because small errors can affect fit, operation, sealing and appearance. The surveyor should also consider access, ventilation, safety glazing, opening arrangements and any signs of structural movement.
Ask whether the work is carried out by the company’s regular installation team or passed to subcontractors. Using subcontractors is not automatically a problem, but responsibility should be clear before the work starts.
5. Why Are You Recommending This Product?
A reliable installer should explain why a particular window or door suits your home rather than simply steering you towards the most expensive option.
For windows, ask about:
- Frame material
- Glazing specification
- Thermal performance
- Ventilation
- Security hardware
- Opening style
- Maintenance requirements
- Colour and finish
You can review different materials and opening configurations on Gallagher’s window installation page.
For doors, ask how the proposed design balances appearance, security, access and energy efficiency. Compare options such as composite, French, patio and bifold doors through Gallagher’s external doors range.
The installer should discuss both benefits and limitations. For example, uPVC windows are durable, energy-efficient and relatively low maintenance, while aluminium may be preferred for slimmer profiles and larger glazed areas. The right choice depends on the property and your priorities.
6. What Exactly Is Included In The Quotation?
A quotation should be detailed enough for you to compare like for like.
Check whether it includes:
- The number, style and dimensions of each product
- Frame material, colour and finish
- Glazing specification
- Handles, locks and other hardware
- Trickle vents where required
- Internal and external finishing
- Removal and disposal of existing products
- Making good around the openings
- Scaffolding or access equipment, if needed
- Certification
- Guarantees
- VAT
- Payment stages
A low initial figure may not represent the lowest final cost if important items are treated as extras.
Avoid relying on verbal promises. Any agreed product feature, installation detail or additional work should appear in the written quotation or contract.
7. What Guarantees And Insurance Protection Are Included?
Ask the installer to explain the difference between:
- Product guarantees
- Glazing guarantees
- Hardware guarantees
- Workmanship guarantees
- Insurance Backed Guarantees
These may have different lengths, terms and exclusions. Find out who provides each guarantee, what it covers and how a claim would be handled.
FENSA states that domestic glazing installers registered with a Competent Person Scheme are required to provide warranty insurance for qualifying installations, protecting the homeowner if the installer ceases trading during the insured period.
8. What Aftercare Will I Receive?
Even a carefully fitted window or door may require a minor adjustment after it has settled into regular use.
Ask:
- Who should you contact if there is a problem?
- How quickly are aftercare requests normally handled?
- Are adjustments covered?
- Are replacement parts readily available?
- How should the products be cleaned and maintained?
- Will you receive operating instructions and guarantee documents?
A local installer with established premises may be easier to contact if you require support later. Gallagher’s serves Milton Keynes and surrounding areas, with its showroom and team based locally. The full service area is available on the Areas We Cover page.
A Quick Installer Comparison Checklist
Before choosing a window and door installer, confirm that you have:
- Checked the company’s trading history and contact details
- Verified its Competent Person Scheme registration where relevant
- Asked about trade body membership
- Received a detailed written quotation
- Understood the product specification
- Confirmed who will survey and fit the products
- Reviewed the guarantees and insurance protection
- Discussed certification and Building Regulations
- Asked about installation times and disruption
- Understood the aftercare process
- Seen samples or working products where possible
- Compared value, not just the headline price
The FENSA installer checklist also provides useful questions for homeowners appointing a replacement window or door installer.
Choose An Installer Who Is Willing To Explain The Details
The best questions are the ones that reveal how an installer works when the sales conversation ends.
Look for clear explanations, written specifications, appropriate certification and realistic guidance about installation and aftercare. A trustworthy window and door installer should help you understand your options without rushing you into a decision.
Gallagher’s is a family-run window, door and conservatory company established in 2001. As a long-standing FENSA member and a member of the GGF, the team combines local experience with recognised customer protections and technical support.
Discuss Your Windows Or Doors With Gallagher’s
To compare products and discuss the questions that matter for your home, visit our showroom in Bletchley or contact the team to arrange a consultation.
