The type of window glazing can be determined in two ways: by using the product information provided by the manufacturer, or through a visual inspection using a flame. If the product data is not available, holding a small flame (such as from a tealight or lighter) close to the window glass can help identify its characteristics.
The number of flame reflections visible in the glass reveals the number of panes in the window. Additionally, the color of the reflections can indicate whether the glazing includes thermal insulation properties.
Here are some typical window types and their characteristics:
Single Glazing:
Common in older buildings, single glazing reflects the flame only once—just one visible flame reflection. However, this reflection doesn’t provide further details about special properties such as thermal or sound insulation.Double Glazing (Installed between 1975 and 1995):
Two pairs of reflections can be seen, totaling four flame reflections. All reflections appear in the same color.Triple-Glazed Insulating Glass:
Three pairs of reflections are visible, resulting in six flame reflections. All six have the same color.Double-Glazed Low-E Glass (Primarily since 1995):
Four flame reflections are visible. The second reflection (when viewed from the interior) has a slight violet tint, indicating the presence of a coated surface for thermal insulation.Triple-Glazed Low-E Glass (Since 2004):
Six flame reflections can be seen. As with the double-glazed version, the second reflection from the inside has a subtle violet tint, pointing to a low-emissivity (Low-E) coating.
To ensure a more accurate assessment, it can be helpful to perform the test under different lighting conditions, as the reflection colors may vary depending on the light. It’s also worth noting that older windows may have been retrofitted with thermal insulation coatings, which can also influence the reflection color.
Source(s):
Maus, R. (2013): Verglasung oder Fenster;
SN (2014): Ein Fenstertausch dauert nicht lang und zahlt sich aus