The thermal transmittance of windows is a basic aspect, which has gained more and more importance due also to the increasing attention rules have given to this topic(¹).
Thermal transmittance simply quantifies the amount of energy (heat/cold) the window allows to penetrate through its surface. The lower the thermal transmittance of a window, the better is the resulting wellbeing indoors, and even more important, the higher is the energetic saving and, as a consequence, the economic benefit. 
The thermal transmittance practically identifies the thermal insulation capacity of the window.

Already since  1998, who sells windows is compelled to supply the Customer with an energetic certification attached to the window delivered. This obligation has become even stronger since the recent introduction of new rules concerning climatic areas(¹). In Italy 6 climatic areas have been identified, and for each of these areas windows are supposed to provide a certain level of energetic performance, depending on the general weather conditions and on the morphology of the area in question.

When it comes to building a new house, or, in some cases, when a house is renovated, the designer has to declare to the joinery supplier the energetic performance required.  For example: For a building located in the municipality of Florence, which belongs entirely to the area D, the minimum energetic performance windows have to ensure must be   3,1 W/m2k (²).

Stenfis is in the position to fully comply to the rules by declaring precisely the energetic performance of her windows (independently from the size and number of sashes). The values declared are based on the test results used to obtain the certification. Stenfis windows offer W/m2k values which are considerably better than the minimum values established by the Law.


(¹) to learn more about this topic, please refer to  D.Lgs. 19.8.2005 n. 192 and subsequent changes and integrations.
(²) the value W/m2k expresses how many Watt (heat measured in Kelvin degrees) the window allows to penetrate through one square meter of its surface.