Windows are where most homes leak heat in winter and gain it in summer — and in Spain, where air-conditioning runs hard from June to September, that shows up directly on your electricity bill. This guide explains Uw and g-value, compares single, double and triple glazing, gives realistic post-replacement savings and payback figures, and shows how grants can cut the upfront cost.
In 2026 you can stack two distinct savings on new windows in Spain: a NextGenerationEU direct grant of up to 40% (around €3,000) and an IRPF tax deduction of up to 60%. This guide explains both, the exact requirements, the paperwork in order, the deadlines, and the mistakes that get claims rejected.
The Uw value is the single most important number on a window quote — it tells you how much heat the whole window lets through. This guide explains Uw versus Ug and Uf, what the units mean, the target figures for each Spanish climate zone, how it ties into CTE rules and grant eligibility, and why in hot regions you must read it alongside the solar g-value.
Argon is the invisible upgrade hiding inside good double glazing — a heavy, inert gas that quietly improves insulation, comfort and condensation resistance. Here is what argon actually does between the panes, how much it changes the Uw value, whether it is worth paying for in Spain's heat as well as its cold, and how to verify it is really in your quote.
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