Window quote jargon explained
Window quotes are full of technical shorthand. Here is the jargon you are most likely to meet, translated into plain English so you can tell whether a specification is generous or bare-bones.
The energy terms
U-value measures how much heat escapes through the window — the lower the number, the better the insulation. A modern double-glazed unit typically sits around 1.2 to 1.6 W/m²K. WER stands for Window Energy Rating, the A++ to E banding you may recognise from appliance labels; it rolls heat loss, solar gain and air leakage into a single grade. Our detailed guide to U-values and window energy ratings unpacks both.
Low-E glass has an invisible metallic coating that reflects heat back into the room. Argon (sometimes krypton) is the inert gas sealed between the panes; it insulates better than plain air. Solar gain is the free warmth the sun adds through the glass — useful in winter, less so on a south-facing room in summer.
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Get into the quote zone →The glass and unit terms
A sealed unit (or IGU, insulated glass unit) is the sandwich of two or more panes with the gas-filled gap between them. The spacer bar is the frame around the edge holding the panes apart; a “warm-edge” spacer reduces cold bridging at the perimeter. Toughened glass is heat-treated to be stronger and to break safely, while laminated glass has a plastic interlayer that holds it together if broken — useful for security and noise. To see when each is worth paying for, read the glass options on your quote.
The frame terms
A casement is a window hinged at the side or top that swings open; a sash slides vertically, as on many period homes. The frame holds everything, and the sash or vent is the opening part within it. uPVC, aluminium and timber are the three common frame materials, each with different costs and looks — compared in our guide to frame materials and finishes. A trickle vent is the small controllable slot that provides background ventilation, now required on most replacements.
The commercial terms
IBG means insurance-backed guarantee — cover that still stands if the installer stops trading. A deposit is the upfront payment, and a stage payment is an instalment paid at an agreed point. FENSA and CERTASS are competent-person schemes that let installers self-certify against building regulations. If you want the full manufacturing-side vocabulary, it is worth reading up on professional-grade window specifications too.
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