How to compare three window specifications confidently
The seven details that should appear in every proposal, common sales tactics, and how to compare specifications between installers.
The seven line items to insist on
A proposal you can actually compare will state: (1) the exact product name and system — Deceuninck 2500, Rehau Total70, Origin OB-72, and so on. (2) The whole-window U-value and Window Energy Rating for each unit. (3) The glazing specification — double or triple, argon fill, low-E coating, warm-edge spacer type. (4) The frame colour and finish, including internal and external where different. (5) The hardware brand and security rating — PAS 24, Secured by Design. (6) The trickle vent specification. (7) The scope of making-good: plastering, redecoration, external sealant, waste removal.
If any of these are missing, ask before signing. A proposal that hides them is deferring important decisions until the fitter is on site.
The tactics to watch for
Time-limited pressure tactics are a sales script, not a reason to rush. A reputable installer gives you space to review the proposed specification and contract terms.
An advertised upgrade can mean the baseline specification was sub-standard. Ask for the exact U-value, hardware and glazing details before deciding.
Beware of proposals that list every window as one undetailed line. Without product-by-product specifications, it is impossible to compare materials, hardware and installation scope properly.
Comparing the specifications
Three proposals will rarely specify identical products. List each installer's system, U-value, glazing specification and hardware side by side so the differences are clear.
Then look at what is not glazing: scaffolding, structural lintels above bay windows, replacement cills, and Building Control notification. These items can surface unexpectedly mid-project if they are not documented clearly at the outset.
The questions to ask before signing
Who installs — direct employees or subcontractors? What is the guarantee, and is it insurance-backed? What happens if the fitter damages plaster or brickwork? Is the deposit protected? What is the payment schedule? Which Competent Person Scheme registers the work? How long between deposit and installation?
A confident installer answers all of these in writing without hesitation. Vague or verbal answers are a signal to keep looking.
Check that the payment schedule, deposit protection and cancellation terms are all written clearly before you commit. Never make full payment before installation.
Differences often come from the product and installation specification rather than workmanship alone. Compare systems, glass, hardware, making-good and guarantees line by line.
Yes. It means the guarantee survives the installer going out of business. A guarantee from a company that closes is worth nothing.
