CEN/TC 129

Date: 2025 −07

prEN 673: 2024/prA1 :2025

Secretariat: NBN

Glass in building — Determination of thermal transmittance (U value) — Calculation method

Glas im Bauwesen — Bestimmung des U-Wertes (Wärmedurchgangskoeffizient) — Berechnungsverfahren

Verre dans la construction — Détermination du coefficient de transmission thermique, U — Méthode de calcul

ICS:

CCMC will prepare and attach the official title page.

Contents Page

European foreword 3

1 Modification to Clause 7.2, “Internal heat transfer coefficient h_i” 4

European foreword

This document (EN 673:2024/prA1:2026) has been prepared by Technical Committee CEN/TC 129 “Glass in building”, the secretariat of which is held by NBN.

This document is currently submitted to the CEN Enquiry.

After :

“This is only applicable if there is no condensation on the coated surface. A procedure for determining the corrected emissivity of a coating is given in EN 12898.”

Add:

“A value of 293,15 K can be assumed for T_s in equation (12), with reference made to Table 7 of ISO 6946:2017.”