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Air permeability in aluminium windows.

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How is air permeability determined in an aluminium window?

Have you ever put the hand near your window and have you felt how the air flew through it? We propose you an experiment: light an incense stick and get close to the window. If the smoke doesn’t rise vertically but it has a lot of turbulences, you can be sure that your window is not airtight (hermetic). For example an old slide window can leak more than 50m3/h m2, a total waste of energy. The more unwanted air that gets into the more air you will have to heat or cool; this could increase in 30% energy consumption. Therefore, it is advisable to install high sealing windows. But… How do we know if an aluminium window is really airtight?

Windows must go through strict quality controls to demonstrate their resistance, insulation and sealing performances. In the case of air permeability, tests are carried out according to standard UNE-EN-1026. Air tightness is defined as the window capability to prevent air from passing through it. This capability is measured on a scale, from class 1, less tightness, to class 4, higher tightness. This classification is very important, because the Technical Building Code (TBC) in the Basic Document of Energy Saving, (HE) required to install, at least, class 1 or 2 windows depending on the Climatic Zone.


 Test procedure


In the test procedure the window is located simulating the actual implementation in the construction, assuring the framework sealing with the building envelope, to analyse the amount of air passing through the window opening joints.

 During the previous hours, specific conditions of temperature and humidity must be maintained. Usually the test is divided in two tests:

I.  First pressures over 100 km/h are applied on the window in strokes, simulating the onslaughts of hurricane-force winds.

II. Then a continuous pressure is applied, starting from 50 Pa and increasing gradually to 300 Pa.

Once the measurements are adjusted to normal temperature and pressure conditions we get the results of the air flow that passes for every meter of joint (VL) and for every m2 of window and they are recorded in the graphic.

*If you are looking for airtight windows, trust in us. Our E-75 Series has Class 4 air permeability (just 3m3/h.m2) and a thermal transmittance of 1,7W/m2K.Without any doubt, we are talking about one of the best aluminium sliding window in the market


Interested links

Sliding E-75 Series (here)


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