3 reasons to invest in the “warm edge”

  /   26.01.2018

     3 reasons to invest in the “warm edge”

“Warm” is definitely the most important word in the whole industry of manufacturers of windows and doors. Energy-saving windows and doors directly affect the cost of heating and reduction of greenhouse effect. One of the key terms appearing in the context of such windows is the famous “warm edge spacer bar”. We will explain this term here and provide 3 important reasons to invest in warm edge spacer bar.

What exactly is “warm edge spacer bar“

All window glass units are provided with the so-called spacer bar that provides sealing for the edges of the glazed panel separating them from each other (in two- or three-pane units). In commonly used windows, standard spacer bars are made of aluminium (low price is an advantage) and showing high heat conductivity, resulting in thermal bridges affecting properties.

     Warm air escapes through the frame from a house, taking away hard earned money of the owners. No-one likes this feeling, which is why window designers have developed a solution where spacer bars are made of materials with of  very good insulation properties. The result is a new solution commonly known as “warm edge”, and glass units made based on this technologies are now called “warm edge” units.

Warm edge criterion according to PN-EN ISO 10077-1

In accordance with the standard PN-EN 10077-1, the edge with improved thermal parameters may only refer to the edge whose distance frame fulfils the following inequality:

Σ (diλi) ≤ 0,007 W/K


di – wall thickness of the material
λi – thermal conductivity coefficient of the material in W/Mk.

The following table shows how the above criterion performs in the frames made of various materials:

material Σ (diλi) warm edge?
aluminium 0.12160 no
steel 0.04000 no
stainless steel 0.00680 yes
plastic 0.00198 yes

It is clear that both aluminium and standard steel spacer bars do not meet the criterion set in the standard, so they cannot be classified as “warm edge” units.

End of the problem with water vapour condensation

Aluminium spacer bars are prone to give the effect of water vapour condensation around window frames in winter time in poorly ventilated rooms. This is the effect of too high difference in temperatures between the external and internal of glazing panes thermal bridge effect of aluminium spacer bars. When spacer bars made of the adequate materials are used, the problem of condensation or humidity on window panes largely disappears, which translates into higher comfort of inhabitants and healthier sleeping.

     However, we must remember that the “warm edge” alone will not provide protection against condensation of water vapour setting on the windows. A proper ventilation of the rooms should also be ensured, which means airing of an apartment and not covering ventilation ducts. If ventilation is malfunctioning, there is always a problem of mould, excess humidity of air, and finally fungi on walls.

Lower costs of heating

It is obvious that old-type windows, which cannot boast with tightness and quality, can drastically increase cost of heating. As much as 20% of heat may escape through windows that are not air tight and prone to draughts.
Replacement of the windows with “warm edge” units is clearly slightly more expensive, but it should be regarded as a wise investment. The one that will soon balance its costs.

Higher durability of windows

Spacer bars also intended to protect the interior of the windows against penetration of humidity or dirt. Special desiccant helps achieve it: argon or krypton. If the spacer bar is not air tight, these gases start to escape and the unit completely loses its insulation properties. Moreover, moisture will enter inside the windows, which is conducive for growth of mould.
A window with mould inside should be immediately replaced because it simply does not fulfil its insulation functions, not to mention its aesthetics. In case of “warm edge windows and doors, these problems do not occur.

To summarise, here are the 3 reasons to invest in the warm edge spacer bar:

improvement in thermal properties of the window: the window will be definitely warmer in comparison with a window with standard aluminium spacer bars;
limitation of condensation of water vapour on the edge of the glass pane;
reduction of heating costs.