What you need to know about window certification

What window certification means and why it matters

Window certification verifies that a window meets established standards for performance, safety and energy efficiency. For buyers, certification is a guarantee that profiles, glazing units and hardware have been tested and deliver the promised properties: thermal insulation, airtightness, sound insulation and durability.

Typical documents and marks

• Declaration of Performance (DoP)
• CE marking and conformity to EN standards (e.g., EN 14351-1)
• Test reports (Uw, air permeability, watertightness, wind load resistance)
• Energy labels and product data sheets

Performance parameters covered by certification

• Thermal transmittance (Uw, Uf, Ug) — affects heat loss and energy bills.
• Air permeability — indicates potential drafts.
• Watertightness — resistance to moisture and leaks.
• Wind resistance and structural performance.
• Acoustic insulation — important for urban living.

What to ask from the supplier before purchase

1. A copy of the Declaration of Performance and test reports.
2. Certification documents and details of the testing laboratory.
3. The exact configuration tested (glass type, gas fill, spacer bars, hardware class).
4. Installation instructions and warranty conditions — improper installation can negate certified performance.

Tip: request originals or high-quality scans with laboratory details and test dates.

How certification affects operation and savings

Certified windows with verified Uw and airtightness values can bring real savings, particularly when combined with proper wall insulation and professional installation. Low thermal transmittance reduces heating needs in winter and improves overall comfort.

Certification alone does not guarantee performance if installation is poor. Gaps in installation, missing sealing tapes or incorrect adjustment of hardware will reduce effectiveness.

Installation matters

• Install windows according to the manufacturer's instructions and local standards for the mounting seam.
• Use vapor and waterproofing tapes on the installation joint.
• Adjust hardware correctly and maintain seals.

How to spot expired or falsified documents

• Verify laboratory details and certificate numbers in certification registries.
• Check test dates — standards evolve and old reports may be outdated.
• Ensure the model in the certificate matches the actual product.

Warning signs

• Missing notified body number or lab contact details.
• Discrepancies between model names or technical data.
• Documents without signatures, dates or identifiable stamps.

Manufacturer certification and testing labs

Manufacturers may certify profiles and components and issue DoPs for final products. Accredited laboratories conduct the tests by measuring thermal performance, airtightness and other parameters under controlled conditions. Ensure tests were performed on samples representative of the finished window.

FAQ — common buyer questions

Do I need certified windows for an older building?

Yes. Replacing windows in an older building with certified units still improves energy efficiency and comfort.

Can I rely on marketing claims alone?

No. Always request test reports and the Declaration of Performance.

Which matters more — frame or glass?

Both: the frame affects structural and overall thermal performance, while the glazing unit determines Ug and acoustic performance.

What if an installer says certification is unnecessary?

Ask for manufacturer's documentation and insist on proper installation. Poor installation can void the benefits of certified windows.

How often should seals and hardware be checked?

Inspect and adjust hardware annually; replace seals as they show signs of wear.

Conclusion

Certification is a key tool for buyers to verify window performance. Request the Declaration of Performance and test reports, verify the laboratory, and ensure professional installation to get the full benefit of certified windows.