How to Compare Quotes from Double Glazing Providers

30 October 2025

When 3 or 4 quotes land in your inbox and the prices cover a few thousand pounds, it is appealing to skim the totals and select the middle. That is where most house owners get stung. I have actually invested twenty years surveying and setting up doors and windows across London, from Victorian balconies in Hackney to warehouse conversions in Southwark and mid-century maisonettes in Barnet. The single greatest error I see is comparing unlike with unlike: shape for shape on the illustration, however not spec for spec. If you want to select relied on glazing specialists London families and architects rely on, you require to translate the detail, challenge the presumptions, and require a like-for-like comparison.
Why quotes differ so widely
On paper, 2 sets of casement windows look similar. Under the surface, you may be comparing softwood beads versus aluminium clip-in beads, basic float glass against low-E glass with argon gas double glazing, or an unbranded hinge against a stainless friction stay from a known producer. Labour also drives difference. A FENSA accredited window installer who uses skilled fitters, pays for correct garbage disposal, and provides a strong aftercare strategy will not come out the like a one van clothing passing whatever to subcontractors. London overheads matter too. A doors and windows suppliers London company with a correct factory in Greater London and a display room in Finchley or Wandsworth pays different costs than a local attire shipping in once a week.

A credible quote itemises the spec so you see where the cost sits: frame product and system, glazing build-up and spacer, U-values, hardware range, finishing and colour, survey and setup scope, accreditation, warranties, and lead-times. If any of these are unclear, the number is not comparable.
Start by repairing the specification
Before you invite prices, decide the efficiency and look you actually need. Architects generally lead this on extensions and repairs, but as a house owner you can set a clear brief and ask each double glazing supplier to price it as written. This stops the bait-and-switch of pricing estimate a spending plan spec to look competitive, then upselling on survey.

For London homes, temperature level swings, traffic sound, and conservation constraints intersect. In a Westminster estate block you may be restricted to like-for-like sightlines, while in a new build in Ealing you can chase after greater energy performance and larger periods. A reputable standard specification for domestic double glazing London residential or commercial properties might be as follows: energy effective windows London with whole-window U-value no worse than 1.4 W/m TWO K for replacement work, low-E glass windows with warm-edge spacer, argon-filled units, and drip vents where ventilation is required under Part F. If you desire the very best thermal performance from double glazing without stepping into triple, try to find BFRC rated glazing suppliers providing A or A+ ranked windows with documented test data, not just marketing labels.

For frames, pick a family. UPVC is still the most cost-efficient for the majority of elevations and can look clever when you pick a slim profile, foiled surfaces, and cool welds. Aluminium doors and windows justify their rate on slim sightlines, durability, and much better colour stability, especially on big patio area doors London house owners love, like sliding doors and aluminium bifold doors London extensions typically feature. If you go aluminium, demand thermally broken aluminium windows and doors. The thermal break is not optional; it is the heart of the efficiency and condensation control.
Decoding frame systems and profiles
Not every uPVC window is equivalent. Entry-level multi-chambered systems can hit Part L targets, but the distinction in between a generic low-priced extrusion and a leading brand shows up in corner strength, gasket quality, and long-lasting colourfastness. Ask which system is being estimated. Names you will see throughout London consist of Eurocell, Liniar, Kommerling, Rehau, and Deceuninck. A Rehau Overall 70 with bonded corners, Q-Lon gaskets, and optional steel support behaves differently from a no-name profile. On aluminium, look for systems like Smart Systems, AluK, Schüco, Reynaers, and Cortizo. Smart's Alitherm and Visofold, or AluK's 58BW and BSF70 suites are commonly utilized by customized window manufacturers London producers due to the fact that they balance expense and efficiency, and can be serviced in the future.

Sightline measurements matter. If you are changing lumber sashes in Islington with uPVC windows London designs, bulkier frames can destroy the percentages. Ask for outer frame and sash deal with widths, transom and mullion sizes, and whether dummy sashes are utilized to accomplish equivalent sightlines. On aluminium, check that slimline claims are backed by area drawings, not just an artist's render.
Glass is not simply "double glazed"
Two 28 mm double glazed systems can act in a different way. The core questions are: what coatings, what gas, what spacer, and what laminate where safety is required. For thermal effectiveness, specify a soft-coat low-E glass inside, a warm-edge spacer, and argon gas double glazing. Krypton is sometimes utilized for narrow cavities, though the expense hardly ever validates it in normal domestic apertures. For south and west elevations, think about solar control coatings if getting too hot is a threat, particularly on large sliding doors London homes use to connect cooking area spaces to the garden. If you live on a busy road in Haringey or near a train line in Lewisham, inquire about acoustic laminates or unbalanced glazing configurations rather than blunt "acoustic glass" claims. A 6.8 mm acoustic laminated pane paired with 4 mm on the other side, separated by a 16 mm argon cavity, can make a concrete difference compared to a symmetric 4/20/4.

Safety glazing is not negotiable near doors, low-level windows, or restrooms. BS 6262 lays out vital locations. Ask your supplier to verify toughened or laminated glass areas on the quote and study drawings. This is where some economical double glazing London provides cut corners to hit a price. Do not accept "as needed on survey" as the only line, make them list it.
U-values and BFRC ratings that really mean something
Whole-window U-value, not centre-of-glass U-value, is the number that dictates compliance. A U-value of 1.2 to 1.4 W/m ² K for replacement windows is a reasonable, efficient target in London. If a quote sings about 0.9 without triple glazing or unique build-ups, you are very likely looking at centre-of-glass just. BFRC ranked glazing suppliers provide labels that tie to specific setups. Request for the precise ranked spec referenced in your quote, and guarantee the same glass mix, spacer, and frame is what you get on-site.

On doors, the thermal space grows. Aluminium front doors and back doors London residential or commercial properties utilize can accomplish outstanding U-values when insulated panels are used. Bifold doors traditionally tested even worse, but modern systems with deep thermal breaks, foam-filled areas, and much better gaskets have actually caught up. French doors London house owners pick for period homes frequently rely on multi-point locking and laminated glazing to keep energy efficiency appropriate while matching heritage aesthetics.
Hardware and ending up: small lines that change the price
I as soon as checked out a home in Richmond where a low quote had actually switched stainless hardware for zinc-plated to shave expenses. Two winters later the seaside air and contamination did the rest. Replacing corroded friction remains throughout a house is not inexpensive. When comparing quotes, keep in mind the hardware brand name and finish. Hoppe, PERIOD, Securistyle, Yale, and Mila all supply trusted item. Key-lockable manages, heavy-duty hinges on taller sashes, kid restrictors on upper floorings in family homes, and robust roller assemblies on moving doors are all worth attention.

On the ending up side, inspect how cills and packers are handled, and whether aluminium windows and doors will be powder layered to a basic such as Qualicoat. If you desire dual colours, be explicit. RAL 7016 outdoors with white inside prevails, but double colouring costs more and has lead-time ramifications. For uPVC, foiled surfaces like anthracite grey, agate grey, or Irish oak make a huge visual difference, and much better providers will keep in mind the exact foil, not just "grey".
Installation scope, waste, and making good
An "set up just" cost and a "supply and fit with making good" cost are not the exact same item. Constantly check whether your quote includes:
Removal and disposal of existing frames and glass, with proof of licensed waste transfer. Internal and external making good: plaster, trims, silicone, and colour matching sealants where required.
Minor plaster repair work are generally consisted of, but redecoration is not. Excellent firms will prime bare plaster and leave tidy lines. If you are working on a noted property in Camden or within a conservation area in Kensington and Chelsea, information on external trims and putty lines, and making use of heritage-approved profiles, need to be explicit. On industrial glazing suppliers London tasks, RAMS, access, and out-of-hours might add expense. Residential operate in tight mews or fourth-floor flats without lifts also impacts install times and rates. Openness here signals professionalism.
Certifications, assurances, and the paper trail
In England, replacement doors and windows need to abide by Building Regulations Part L, Part F, and where relevant Part Q for security in brand-new houses. Domestic replacements in existing homes typically need a compliance certificate. FENSA licensed window installers and CERTASS authorized double glazing firms can self-certify and offer you a certificate within weeks of conclusion. If a supplier does not provide FENSA or CERTASS, you will need to acquire a regional authority building control sign-off, which includes time and expense. Some London boroughs are quicker than others; Lambeth tends to be pragmatic if paperwork is complete, while Westminster can be precise on heritage fabric.

Ask for:
Proof of FENSA or CERTASS registration with existing business name and number. Insurance-backed assurances for deposit and workmanship. Ten-year assurances are standard in our trade; the better firms likewise sign up product guarantees with the system house or glass supplier. Product-specific warranties: powder coat surface service warranty on aluminium (typically 10 to 25 years depending upon area category), sealed system warranty (5 to 10 years), hardware warranties.
Paperwork safeguards resale. More than as soon as I have been contacted us to retrofit compliance documents for a flat sale in Tower Hamlets due to the fact that the original installer never issued a FENSA certificate. It bores and quickly avoided.
Reading the illustrations and schedules like a pro
Ask for and compare elevation illustrations and a schedule that lists each opening with measurements, handing, opening instructions, glass type, ventilator, drip vent size, and safety marking. The schedule should align with what is measured on site. I flag two typical traps:

First, trickle vents. Some quotes omit them to achieve a cleaner appearance and lower U-values on the label, then add them at survey due to the fact that Part F needs background ventilation in particular situations. Suddenly the tidy look is gone, and the price jumps. If you require vents, define the type and air flow ranking in advance. Acoustic drip vents exist, but they are bulkier and pricier.

Second, cill projections. Victorian brickwork in places like Waltham Forest often requires deeper cills than modern-day stock. A standard 150 mm uPVC cill may not cover well, leading to leak problems. Make certain cill size is defined to match your wall build-up, not just a default.
Price bands you can use as a sense-check
Costs move with aluminium and glass markets, however there are workable varieties for London since this year:
Basic uPVC windows and doors with A-rated double glazing, white surface, standard sizes, and simple installation: roughly ₤ 500 to ₤ 800 per window provided and fitted, depending on size and floor level. Bay windows and shaped frames cost more. Foiled uPVC windows and doors, improved acoustic or laminated glazing, and trickle vents: ₤ 700 to ₤ 1,100 per opening. Aluminium windows London jobs with thermally broken profiles, standard colours, and A-rated glass: ₤ 900 to ₤ 1,600 per window on common sizes; big sliders and shaped units scale sharply. Aluminium bifold doors London suppliers provide, 3 to four panels around 3 to 4.5 metres broad: ₤ 3,000 to ₤ 6,000 fitted, depending on system, hardware, and glazing. Premium European systems can exceed ₤ 8,000. Sliding doors London extensions, two-panel with slim interlocks, around 3 metres: ₤ 3,500 to ₤ 7,000 depending on system and glass specification.
If your quotes fall outside these bands, either the scope is unusual or someone is filling margins or, on the other hand, cutting a corner.
How suppliers structure their numbers
Some double glazing business London based will break out supply, install, access, completing, and certification. Others present a single sum. I choose to see the breakdown; it enables you to challenge specific items. If crane hire is included for a third-floor moving door set up in Battersea, reasonable enough. If there is a mysterious "file handling cost", push back.

Payment terms likewise vary. A deposit of 25 to 40 percent is normal, with balance on conclusion. Be wary of extremely high in advance deposits without an insurance-backed plan. On bespoke aluminium doors London buyers commission with uncommon colours or imported systems, a higher deposit can be affordable, however it ought to come with clear lead-times and factory order verifications. Made to doorwins windows and doors https://www.tumblr.com/doorwinslondonltd measure windows London projects must still bring practical lead-times: uPVC typically 3 to 6 weeks from study, aluminium 5 to 10 weeks, longer for special finishes or triple glazing.
When "inexpensive" meets "sustainable"
Sustainable glazing London conversations are often framed only around U-values. Genuine sustainability consists of sturdiness, reparability, and embodied carbon. Aluminium has greater embodied energy however lasts years and can be recycled. uPVC has actually enhanced recyclate material and can be very efficient at lower upfront cost. Timber and alu-clad wood sit in a different conversation entirely, however if you are weighing uPVC versus aluminium windows and doors, acknowledge the context. For example, on a small rear extension in Lewisham, a thermally broken aluminium slider may be the ideal require slender sightlines and robustness, while uPVC windows somewhere else keep budget plan and carbon in check. Ask your provider about the glass supply chain too. A double glazed units manufacturer London based, utilizing Saint-Gobain or Pilkington float with warm-edge spacers from Swisspacer, is much easier to support with spares and warranty than an unknown imported unit.
How to require a like-for-like comparison
The fastest method to compare fairly is to develop a short specification sheet and ask each supplier to confirm they are pricing to it, plus any advised alternatives in a plainly apart section. The spec sheet needs to include:
Frame system and colour, inside and out, with exact profile name. Glazing accumulation, coating, gas fill, spacer type and colour, and any acoustic or safety requirements. U-value target and BFRC rating for the entire window or door. Hardware brand and finish, locking points, and any special manages or kid restrictors. Ventilation method, drip vent designs and airflow. Cill and trim details, and making great scope. Certification route (FENSA or CERTASS), assurance lengths, and insurance-backed warranty. Lead-time from order, survey process, and proposed setup duration.
Then, demand a schedule with per-opening prices. Swelling sum estimates conceal cross-subsidies. If a supplier will not simplify, that informs its own story.
Situational judgment: heritage, security, and industrial realities
In conservation or noted settings, you may need to work with customized window producers London professionals who can reproduce sightlines and putty information in slimline aluminium or bespoke wood with slimline double glazing. Costs jump, and lead-times extend. Ask for samples and references. In locations where Part Q security is required, search for PAS 24 certified doors and windows and Safe by Design choices. Be clear that laminated glass and updated locking matter more in ground floor and quickly accessible windows. On shopfronts and little business work, the industrial glazing suppliers London designers use will typically price stick curtain wall or thermally broken shopfront systems with ranked doors. If your project straddles domestic and commercial components, guarantee the same provider can manage both, or handle user interfaces carefully.
Red flags I look for on quotes
I keep a brief psychological list when I examine quotes for clients and friends in London.
The company will not mention the precise profile system or glass spec, only "A-rated". "No FENSA" with a promise to lower rate if you avoid certification. Unrealistic U-values and solar control claims without data sheets. Vague installation scope, specifically on making great and waste disposal. Unbranded hardware and no reference of warranties. Low deposit coupled with aggressive discounting if you sign today, which is often an indication of pressure selling instead of stable pricing.
A second classification is completely legal however requires caution: very long-distance installers quoting London jobs. They can in some cases use lower rates but might struggle to service aftercare. If you select them, demand written service commitments.
Local knowledge pays dividends
A London window and door company that works routinely in your district will know the quirks. In Hackney, internal reveals in ex-local authority obstructs frequently hide steel, so repairing techniques alter. In Camden, coordinators scrutinise external sightlines on front elevations. In Greenwich and along the river, salt air needs better hardware and finish warranties. Anybody estimating you need to be able to talk to these points. If they can not, you are not handling the very best double glazing suppliers for your context.
Case notes from recent projects
A balcony in Shepherd's Bush: the house owner had three quotes for uPVC sashes and a French door at the back. The most affordable was ₤ 6,200, the highest ₤ 8,950. The low quote had a 150 mm cill across all windows, which would have left a short projection over the London stock brick and risked water staining. It likewise omitted drip vents and listed "A-rated system" without specifying low-E type or spacer. We priced at ₤ 7,600 with 180 mm cills on the much deeper exposes, acoustic drip vents in the bed rooms due to a neighboring bus path, and laminated glass on the French door. Over a winter, the customer reported quieter rooms and no sill drips. The apparent ₤ 1,400 saving would have evaporated in restorative works.

A loft conversion in Walthamstow: aluminium windows London spec with slim frames interested the designer, but the first quote put a Schüco system on a modest budget plan, pressing price toward ₤ 13,000. After discussion, we priced an AluK 58BW suite with the exact same RAL finish, A-rated glazing, and PAS 24 hardware at ₤ 9,800. Efficiency targets were fulfilled, sightlines were acceptable to the planner, and the distinction moneyed better insulation in other places. This is not about selecting the most affordable, it has to do with matching system to requirement.

A kitchen area extension in Bromley: the client dreamt of a 5.5 metre two-panel moving door with 30 mm interlock. The quotes varied from ₤ 7,500 to ₤ 14,000. The lower figure was a non-thermal industrial slider, completely inappropriate for domestic thermal expectations and accountable to condensation. We strolled the customer through thermal break areas and Uw computations. They selected a premium thermally damaged slider at ₤ 11,800. Energy expenses and convenience validated it, and the door moves effortlessly even with large panes.
What to ask previous customers and how to verify
Most providers will offer referrals. Ask to talk to a customer whose task is at least a year old in your area. The shine diminishes in year two if the sealing was bad or the hardware was low-cost. Drive past a finished job to judge sightlines and finishing. Cross-check Business House for the trading entity and age. FENSA and CERTASS both have public search tools where you can validate active subscription. For BFRC, ask for the label associated to your specific setup and validate it versus the database instead of accepting a generic brochure image.
A short checklist for comparing quotes Confirm the precise frame system, finish, and section sizes, with drawings. Match glazing specs line by line, including finishings, gas, spacer, acoustic or security requirements, and documented whole-window U-values. Verify FENSA or CERTASS registration, guarantee lengths, and insurance-backed cover. Align setup scope: access, waste, making good, trickle vents, cills, and trims. Demand per-opening rates and clear lead-times, and difficulty unclear exclusions. When to walk away
If a supplier refuses to offer system names, evades accreditation, or presses for an on-the-spot signature with a disappearing discount, walk. London has plenty of windows and doors suppliers, and the trustworthy ones are comfortable addressing uncomfortable questions. A little friction in advance generally indicates a smoother job later.

The comparison process is not glamorous, however it is the part that saves you money and sorrow. Whether you are refreshing uPVC doors London large in a rental portfolio or commissioning custom aluminium doors London designers define for a high-end refurbishment, the approach is the same. Repair the specification, check the paperwork, scrutinise the information, and examine the people. Windows and doors are a 20-year choice. A mindful week now, looking beyond the heading numbers, spends for itself often times over.

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