Energy efficient windows – a necessary investment

To the untrained eye, one might only think of windows from an aesthetic point of view, but this aspect of a house is far more important than one may realise. Windows are one of the main points of energy loss in a traditional house, and they are also a source of condensation in winter due to the fact that the windows are a direct contact point with the outside temperature. This leads to mold which is highly dangerous. Additionally, they represent the means by which a house receives “free” heating from the sun.

Not only do windows play a role in the overall energy efficiency of a house, but specifically they have a significant impact on airtightness. You have probably heard of double glazing, which is now a more common characteristic of windows in Chile. Yet there are so many other factors to take into consideration and this is a HUGE investment in an energy efficient house and one needs to have all the facts available to make the best decision. In our case, the windows represent 7% of the total cost of our house, but their impact goes far beyond the purse strings.    

We were very happy when our windows finally arrived, almost a month late due to a few complications in the stock of the materials that had to be imported.

After a lot of research we decided to use Deceuninck´s Legend range of windows, which are certified Passivhaus and have a range of properties that improve airtightness and reduce thermal bridges since the frames are PVC and not metal.

Solven’s contractors installing our windows

The frames are 80mm thick, with 6 insulation chambers, a high level of airtightness and a thermal transmittance factor of less than 1,12W/m2K. For those less technical people such as myself, this basically means that air can´t move through the frame from the outside to the inside of the house or visa versa.

This is an image from the Passivehaus database. On the left it shows the different chambers that act as insulation, and on the right it shows clearly how the window frames prevent heat loss (Source:

I can also say that I am really impressed with the closing mechanisms, you definitely feel the windows sealing well when you close them, and this is especially evident with the large sliding doors we have in the living and dining room. Sliding doors are normally notorious for air infiltrations, but these are completely airtight!

Finally, apart from the properties of the frames, the glass is also important. We chose double glass with gas argon in the interior chamber between the two panes. This is a neutral gas that is denser than the atmospheric air and improves the noise insulation and thermal efficiency of the windows.

In total, the two panes of glass and the chamber filled with argon gas are 22,5mm thick. As a comparison, a normal pane of glass in an average window is 5mm thick.

In addition, we applied a low-emissivity coating (Low-E) which minimizes the amount of infrared and ultraviolet light that goes through the glass, but does not reduce the amount of light that enters. Basically this coating helps to maintain the glass close to the interior air temperature, thus minimizing the creation of air currents between the exterior and interior of the house.

Overall, for those of you that are more technical, our installed windows (frames and glass) have a Uw-value of 1,1, whereas a normal, traditional window has a thermal transmittance value of around 5,6-5,8. A HUGE difference when it comes to energy efficiency.

To sum up, I really hope that after reading this post you understand the importance of investing in good quality windows with the right characteristics. I find it really frustrating when people say that these aspects are far too expensive for a “normal” house, yet they are only considering the short term construction costs and not the long term operational costs and overall comfort when we are living in our home.

Windows are an investment and not a luxury.

The north side of the house with the windows installed

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