Your Window Quote, Translated: Twelve Terms to Check Before You Pay a Deposit

Why the wording matters

A window quote is a contract in waiting. The problem is that it often arrives in the language of the trade: U-values, g-values, warm-edge spacers, tolerances and registration schemes. None of these terms is deliberately mysterious, but together they can make two quotes hard to compare and can hide gaps that become expensive later.

The answer is not to become a glazing specialist. It is to ask for the right clarifications in writing before you pay a deposit. The twelve lines below are a practical translation.

1. Whole-window U-value (Uw)

This is the heat-loss figure for the complete window, including frame, glass and spacer. A centre-pane Ug figure describes only the glass and will usually look better. Ask: is this the whole-window Uw value, and what frame and spacer does it assume?

2. Solar factor (g-value)

The g-value describes how much solar energy passes through the glass. It matters for south, east and west-facing windows, where summer overheating and winter solar gain are both relevant. Ask: what is the g-value, and is it the same for every elevation?

3. Warm-edge spacer

The spacer is the bar that separates the panes around the edge of a sealed unit. A warm-edge spacer reduces heat loss at that edge and helps limit condensation. Ask: what material is the spacer, and is it included in the quoted U-value?

4. Argon fill

Argon is an inert gas used between panes to improve insulation. It is not a permanent guarantee unless the unit is well sealed. Ask: is argon fill included, what concentration is specified, and what warranty covers gas retention?

5. Low-emissivity coating

Low-E coatings reflect heat back into the room while allowing daylight through. Different coatings perform differently, and the coated surface must be correctly positioned. Ask: which low-E product is being supplied, and does the quote name it rather than simply saying low-E glass?

6. Trickle vents

Trickle vents provide background ventilation. They are not the same as opening a window to purge a hot room. Their acoustic and thermal performance varies. Ask: what equivalent area is provided, are they controllable, and have acoustic considerations been allowed for?

7. Sill extensions and cavity closers

A sill extension projects beyond the wall to throw rainwater clear. Cavity closers seal the gap between the new frame and the wall structure. These are small items that matter for weatherproofing. Ask: are sill extensions and cavity closers included, and what length and finish are specified?

8. Dimensional tolerances

Quotes often state that sizes are subject to survey and normal manufacturing tolerances. That is reasonable, but the allowance should be clear. Ask: what tolerance applies, who is responsible for making good if the opening is out of square, and are those costs included?

9. FENSA registration or equivalent

FENSA is a Competent Person Scheme for window installation in England and Wales. Registration means the installer can certify compliance with Building Regulations without a separate local authority application. Ask: will I receive a FENSA certificate or equivalent, and is the guarantee insurance-backed?

10. Making good, plastering and decoration

Removing old windows disturbs plaster, reveals and seals. A quote may include making good, or it may leave the homeowner to arrange it. Ask: what making good is included, how far does it extend, and is decoration included or excluded?

11. VAT and disposal

VAT and the removal of old windows and frames should be shown clearly. A low headline price can become less attractive once these are added. Ask: is VAT included, and is disposal of the old units and packaging included in the price?

12. Guarantees and deposit protection

A guarantee is only as good as the company and policy behind it. Deposit protection matters too. Ask: what is covered, for how long, by whom, and is the guarantee insurance-backed? How is my deposit protected, and what payment stages apply?

Before you sign

A fair quote should be clear enough to compare line by line. If a term is unclear, ask for it in writing and keep the reply with the quote. A reputable installer will not mind. The aim is not to find the cheapest headline figure, but to understand exactly what is being supplied, installed and guaranteed before any deposit changes hands.