This European Standard specifies a calculation method to determine the thermal transmittance of glazing with
flat and parallel surfaces.
This European Standard applies to uncoated glass (including glass with structured surfaces, e.g. patterned
glass), coated glass and materials not transparent in the far infrared which is the case for soda lime glass
products, borosilicate glass and glass ceramic. It applies also to multiple glazing comprising such glasses
and/or materials. It does not apply to multiple glazing which include in the gas space sheets or foils that are far
infrared transparent. The procedure specified in this European Standard determines the U value) (thermal
transmittance) in the central area of glazing.
The edge effects due to the thermal bridge through the spacer of a sealed glazing unit or through the window
frame are not included. Furthermore, energy transfer due to solar radiation is not taken into account. The
effects of Georgian and other bars are excluded from the scope of this European Standard.
The standard for the calculation of the overall U value of windows, doors and shutters (see EN ISO 10077-1
[1]) gives normative reference to the U value calculated for the glazing components according to this
standard.
For the purpose of product comparison, a vertical position of the glazing is specified. In addition, U values are
calculated using the same procedure for other purposes, in particular for predicting:
heat loss through glazing;
conduction heat gains in summer;
condensation on glazing surfaces;
the effect of the absorbed solar radiation in determining the solar factor (see Bibliography, [2]).
Reference should be made to [3], [4] and [5] or other European Standards dealing with heat loss calculations
for the application of glazing U values determined by this standard.
A procedure for the determination of emissivity is given in EN 12898.
The rules have been made as simple as possible consistent with accuracy.
BS EN 673:2011 Referenced Document
EN 12898 Glass in building - Determination of the emissivity*, 2019-03-01 Update
EN 674 Glass in building - Determination of thermal transmittance (U value) - Guarded hot plate method*, 2011-06-01 Update
EN 675 Glass in building - Determination of thermal transmittance (U value) - Heat flow meter method*, 2011-06-01 Update
BS EN 673:2011 history
2011BS EN 673:2011 Glass in building. Determination of thermal transmittance (U value). Calculation method
1998BS EN 673:1998 Glass in building - Determination of thermal transmittance (U value) - Calculation method