Window energy ratings: what the A+ actually means
Windows in Portugal have their own energy label, on a scale from F to A+. It is voluntary, free for the buyer — and it condenses three numbers you should know even when there is no label at all.
What the CLASSE+ label is
CLASSE+ is the energy label run by ADENE — Portugal’s energy agency — for products with no mandatory labelling scheme, and windows are its main case. It works like the label on a fridge: a colour scale from F (least efficient) to A+ (most efficient), designed, in ADENE’s own words, to give consumers a simple, easy-to-read reference.
Three things set it apart from a marketing badge. It is assigned from the product’s test results — the same tests behind the CE marking. Every labelled window carries a unique identification code and a QR code that opens its technical record on ADENE’s portal — verifiable years after the job. And it costs the buyer nothing: the scheme is funded by the companies that join.
The weak point is in the scheme’s nature: it is voluntary. A label only exists if the company that makes or sells the window joined CLASSE+. We come back to that below, because it is the part that causes the most confusion at quote time.
The numbers behind the letter
The class is a weighting of three tested parameters, following the ISO 18292 methodology. The fourth appears on the label, but stays out of the calculation.
Uw — how much heat escapes
The thermal transmittance of the complete window: frame, glass and seals working together. The lower, the less heat you lose in winter. In the published case studies of class-A windows, Uw sits between 1.2 and 1.6 W/m²K.
Solar factor (g) — how much sun gets in
The share of solar energy that passes through the glass. In winter it is free heating; in summer, with direct sun, it is overheating. That is why the label shows winter and summer comfort separately — the same window behaves differently in each season.
Air permeability — how much air leaks in
The airtightness class of the closed window, from 1 to 4. This is the figure that separates a well-made, well-fitted window from one that whistles. The class-A windows in the published examples are all class 4 — the best.
Rw — how much noise stays outside
Acoustic attenuation in decibels. It does not enter the energy-class calculation, but it appears on the label as a pictogram, because it is one of the first things people want to know. Our acoustic glass guide explains what the numbers mean in practice.
The reference values quoted come from case studies published by the trade magazine Novoperfil on labelled windows — they are not official class boundaries. ADENE does not openly publish the exact thresholds between classes; what matters is the order of magnitude and, above all, that the glass and the seals weigh more than the colour of the sticker.
Why not every window has a label
According to the trade press, more than 140 companies have joined CLASSE+, together representing over half of Portugal’s window-frame business. That is a lot — and it also means nearly half the market sells windows without a label, excellent windows included.
Both readings follow, and both are worth making. If the company is a member, the label is free and you are entitled to demand it — ADENE is explicit: faced with “we don’t issue labels because they’re not mandatory”, the consumer should insist, because the label exists precisely so they can decide informed. If the company is not a member, the absence of a label says nothing about the window — the same tests exist regardless, because CE marking requires them; the values just live in the technical documentation instead of on a sticker.
We are in the second group: JanelaFix is not a member of the scheme, so we do not issue the label. We say it here as plainly as we say it at the survey — and we put in writing the numbers the label would summarise: the Uw of the complete window, the glass composition, the air-permeability class and the manufacturer’s CE documentation.
The label and state grants: what is still true
One of the most common searches on this topic ties window classes to the Fundo Ambiental. The link did exist: Casa Eficiente 2020, IFRRU 2020 and the Energy Efficiency Fund calls required CLASSE+-labelled windows to unlock funding. That is how the label earned its reputation as a door to subsidies.
The part old articles leave out: those programmes are closed. As of August 2026, we know of no active support programme for residential window replacement. Much of what search results surface — generous co-funding percentages, caps of €1,500 or €2,000 — describes calls from 2018 to 2021, with applications shut for years.
If a new programme opens, its official notice will say whether a label is required and at what class. Until then, plan with real prices — our pricing guide has values per m² and per flat type, without counting on grants that do not exist.
What to ask for in a quote, with or without a label
The label is a convenient summary, not a requirement. What decides your comfort are the values behind it, and you can — and should — ask any company for them, member or not:
The Uw of the complete window, not just the Ug of the glass. A 1.0 glass unit in a weak frame makes a mediocre window, and some quotes show only the flattering number. The air-permeability class, from 1 to 4 — the difference between airtight and “closes, but you can feel it”. And the CE-marking documentation (EN 14351-1), which is mandatory and where these values must appear.
Whoever answers all three questions without hesitating has done the tests. Whoever dodges all three — coloured sticker in the catalogue or not — is asking you to buy blind.
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Frequently asked questions
No. ADENE answers this in the first line of its own FAQs: the CLASSE+ label is not mandatory and costs the buyer nothing. It is a voluntary scheme — companies join if they choose to. What is mandatory is the window’s CE marking (EN 14351-1), and it is precisely the CE-marking tests that produce the values the class is calculated from.
Not necessarily. The label only exists if the company joined the scheme; its absence says something about the company, not about the window. An unlabelled window can have exactly the same glass, profile and test results as an A+ one — the difference is that the values sit in the technical documentation instead of on a coloured sticker. What you should always demand, label or not, are the numbers: Uw, solar factor and air-permeability class.
It depends on where the difference comes from. Between distant classes (C to A) you will feel it in the bills and in comfort. Between A and A+ the performance gap is small and the surcharge sometimes is not — ask for the Uw values of both and compare. A tenth of a point of Uw does not justify any price; a better glass unit or a higher airtightness class might.
The programmes that required it — Casa Eficiente 2020, IFRRU 2020, the Energy Efficiency Fund calls — are closed. As of the time of writing (August 2026) we know of no active support programme for residential window replacement in Portugal. If you find articles promising co-funding, check the date: most describe schemes from 2018–2021. When a new programme opens, its official notice will state whether the label is required.
Every CLASSE+ label carries a unique identification code and a QR code. The QR opens the product’s record on ADENE’s portal, with the technical characteristics and the supplier — verifiable even years after installation. If a sticker has no verifiable code, it is not a label from the scheme.
No — we are not a member of the scheme, and only member companies can issue the label. What we hand over is the information the label summarises: the Uw of the window we quote, the glass composition, the air-permeability class and the manufacturer’s CE documentation. Same tests; different format.
Three questions are enough: what is the Uw of the complete window (not just the glass); what is the air-permeability class; and what CE-marking documentation comes with the window. A serious manufacturer answers all three without hesitating, because the values come from the mandatory tests. Our <a href="/en/guides/how-to-compare-window-quotes/">quote-comparison guide</a> has the full checklist of what a proposal must contain.
No. The energy certificate (SCE) rates the whole dwelling and is mandatory when selling or renting; the window class rates one product and is voluntary. They are related: replacing poor windows with good ones improves the home’s rating at the next certificate, and the assessor can use the windows’ data — including the label’s, if there is one — in that calculation.
Prefer numbers to stickers?
Itemised written quote with the window's Uw, the glass composition and the manufacturer's CE documentation.