What Distinguishes a High-Quality Window?

Two windows that look alike can have very different performance and lifespans. To compare quotes objectively, here are the criteria that really matter.

1. Thermal performance

• Uw: heat loss of the complete window in W/m².K. The lower the better; a Uw of 1.3 or less is a good benchmark in renovation.
• Sw: the solar factor shows how much of the sun’s heat gets in. A high Sw is useful on south façades in winter; a lower Sw limits overheating on west façades.
• Glazing: low-E coating, argon gas and a warm-edge spacer are now standard.

2. The AEV rating

It rates Air permeability, water tightness (Eau) and wind resistance (Vent). The higher the classes, the better the window copes with its exposure. In windy areas or on high floors, it is essential.

3. Certifications

CE marking is mandatory. Voluntary certifications such as the French NF mark with performance labels also certify regular factory inspections, adding assurance of consistent quality.

4. Frame design

• PVC: number of chambers, wall thickness, presence and section of steel reinforcement.
• Aluminium: an efficient thermal break.
• Timber: species, laminated construction and quality of the factory finish.

5. Hardware

Branded hardware, adjustable in three dimensions with several locking points, determines ease of use and long-term airtightness. Also check anti-burglary options.

6. Gaskets

Flexible, durable gaskets, ideally double, that can be replaced without removing the window.

7. Installation

The best window is only as good as its installation: packing, fixing, sealing and adjustment to good practice (DTU 36.5 in France). An RGE-certified installer is also required for grants.

8. Warranties

Warranty length on profiles, glazing and hardware, spare-part availability and after-sales service all indicate a serious manufacturer.

In short

Uw, AEV, certifications, hardware and installation: ask for this information on every quote. It is worth far more than a sales pitch or a spectacular discount.