The new UNE-EN 673:2025 standard is now available which specifies a calculation method for determining the thermal transmittance (U value) of glass with flat, parallel faces in a vertical position in the glazing.

U values are also calculated using the same procedure for other purposes such as predicting:

- Heat losses or gains through the glass

- Condensation on glass surfaces

- Effect of absorbed solar radiation in determining the solar factor

The standard applies to: uncoated glass (including glass with structured surfaces, e.g. patterned glass), coated glass and materials not transparent to the far infrared spectrum as in the case of soda-lime glass, borosilicate glass, ceramic glass, alkaline earth silicate glass and aluminium silicate glass products. 

It additionally covers insulated glazing, including its glass and materials.