What is the U-value of doors and windows? Under the new EU EN 14351 regulations, choosing the wrong U-value may lead to order returns!
In the EU window and door market, the K-value (heat transfer coefficient) is the core indicator for measuring the thermal insulation performance of Windows And Doors. The lower the numerical value, the stronger the ability of windows and doors to block heat loss, resulting in warmer indoor spaces in winter and cooler ones in summer, while also helping users reduce energy consumption. The updated EU EN 14351 regulation in 2024 imposes stricter mandatory requirements on the K-values of windows and doors in different climate zones. If the supplied K-value does not meet the standard, the product will not only fail customs clearance but may also directly trigger customer returns and even face heavy fines.
I. Understanding Window K-Values in 1 Minute: The 'Insulation Code' Behind the Numbers
Definition: The unit of K-value is W/(㎡·K), which represents the number of watts of heat passing through 1 square meter of windows per hour when there is a 1℃ temperature difference between the inside and outside.
Key Comparisons:
Ordinary single-glazed Window Doors have a K-value of approximately 5.0-6.0 W/(㎡·K), with poor insulation and no longer meeting the requirements of most regions in the European Union;
Mainstream double-insulated Glass Window doors have a K-value of approximately 1.8-2.8 W/(㎡·K), which can meet the standards of temperate regions in the European Union;
High-end triple-glass two-cavity + wooden structure window doors have a K-value as low as 0.8-1.5 W/(㎡·K), suitable for cold regions in the European Union (such as Northern Europe).
User Perception: Taking Berlin, Germany (average winter temperature -2℃) as an example, window doors with a K-value of 1.5 save about 300 euros in heating costs per household annually compared to those with a K-value of 2.5. This is also the core reason why European Union users prioritize low-K-value products.
II. EU EN 14351 New Regulation: K-value Requirements Draw Red Lines by Region
The EU's new EN 14351 regulation in 2024 no longer adopts a one-size-fits-all approach; instead, it sets K-value upper limits based on different climate zones. Choosing incorrectly or failing to meet the standards will directly impact orders:
In cold regions (e.g., Sweden, Finland): The K-value of doors and windows must be ≤1.3 W/(㎡·K), and must be paired with Low-E coated glass. If the supplied K-value is 1.5, even if other product performance is qualified, it will be rejected due to non-compliance with local energy-saving regulations.
In temperate regions (e.g., Germany, France): The K-value requirement is ≤1.8 W/(㎡·K). Some countries (e.g., Germany) also require the overall window K-value to match the wall K-value to avoid the 'thermal bridge' effect.
In subtropical regions (e.g., southern Spain): The K-value requirement is relatively lenient (≤2.5 W/(㎡·K)), but must simultaneously meet the solar heat gain coefficient (g-value) ≤0.5, balancing insulation and sun protection.
Certification requirements: The new regulation mandates that all doors and windows entering the EU market must be accompanied by a K-value test report (issued by EU-recognized laboratories such as Germany's IFT and France's CSTB). Products without a report or with report data inconsistent with the actual product will be deemed 'non-conforming products'.
