JANUARY 2025
Deferring the application of EN 673:2024
Glass for Europe wishes to highlight issues affecting the implementation of EN 673 and EN 410, which are used to calculate glass thermal and photometric properties and give recommendations to align the application dates of both standards to avoid disruptions for involved stakeholders.
These standards were intended to be updated and published concurrently due to interconnected changes in the internal heat transfer coefficient calculation (alignment with EN ISO 6946). However, significant challenges have delayed the revision of EN 410 (publication expected in 2026) but the revised EN 673:2024 was published in November 2024.
1. Issues created by the current misalignment
The main technical issue is that thermal calculations (U-values) performed using EN 673:2024 will not be aligned with photometric calculations based on the current EN 410 since the heat transfer coefficient calculations differ. Users will encounter inconsistent results, undermining the reliability and coherence of performance assessments.
This also creates more practical challenges; EN 673 and EN 410 usually rely on the same IT tools for calculations. Updating these tools to reflect the changes in EN 673:2024 without simultaneously updating EN 410 is not feasible. This issue affects all software, regardless of the developer, and includes tools used by Notified Bodies for regulatory compliance.
This situation creates a significant risk of operational disruption across the flat glass industry, impacting manufacturers, software developers, and regulatory bodies alike.
2. Recommendation
To address this issue, Glass for Europe proposes to defer the application of EN 673:2024 until the revised EN 410 is published. The following warning should ideally be inserted in the website of the National Standardisation Organisation on the page where EN 673:2024 can be bought:
“This standard is not yet applicable pending the publication of the revised version of EN 410. The calculation of the internal heat transfer coefficient has been changed in both standards. For the sake of consistency, the changes should be made in the calculations at the same time for both standards. The publication of the revised version of EN 410 is expected no later than May 2026. In the meantime, EN 673:2011 should be used.”
This approach minimizes disruption and safeguards the integrity of performance assessments in the flat glass industry.
Glass for Europe is committed to collaborating with all relevant parties to implement this recommendation or to discuss any other solutions to solve the above-mentioned issues.