U-value of windows - differences

Hello,

we are currently building according to Kfw70 and our standard includes triple-glazed windows with a U-value of 0.9. Now, I have often read that there are of course better windows, for example with a U-value of 0.6.

We have a lot of windows in our house, especially large fronts facing south and west. All windows can be shaded. But that's just a side note.

I am now wondering if there is a big difference regarding energy loss in winter / solar gains in summer if we opt for somewhat better windows, even if we might have to pay an additional charge.

Is it possible to quantify this somehow? Or is it negligible?
What do you think?

We have renovated according to KFW 100 and also installed windows with a Uw of 0.9, which are triple glazed with warm edge spacers and are actually completely sufficient. By the way, the glass has a value of 0.6 (Ug). So it does make a difference whether you mean the U-value for the glass or for the window. In the south, by the way, we used a different glass called Solarwhite, which supposedly lets in more sun. Ultimately, it depends on how much of a surcharge is charged when switching from Uw (!) 0.9 to Uw 0.6. I think that will probably be disproportionately high?

Hmm, we have a Kfw70 house, nearly reaching 55 (as the experts said back then) We only have double glazing everywhere with a U-value >1

How many sqm is it? This can be quantified very precisely, what is theoretically saved... e.g. 0.3 W/sqm K would be with 10 sqm window area on a crisp winter day with -10°C = 10 sqm * 30K * 0.3 W = 30 W per hour -> 0.660 kWh -> 4.6 cents

How many sqm are there? You can quantify very precisely what is theoretically saved... e.g. 0.3 W/sqm K would be for 10 sqm window area on a crisp winter day with -10°C = 10 sqm * 30K * 0.3 W = 30 W per hour -> 0.660 kWh -> 4.6 cents

But then you attached the costs for the temperature change to the windows, right?

The U-value of 0.6 apparently only applies to the glass - that is the pane and not the entire window (the frame is usually the weak point). Currently, there are windows (triple-glazed) with a U-value of 0.84 - these are among the top models in terms of frame construction and are still somewhat affordable. It goes even lower if a special gas mixture is used between the panes. However, this always becomes more expensive.

But you also have to ask yourself whether it is economical. Are you planning with subsidies that require a certain value to be reached? If yes, then the windows are a relatively cheap lever to improve further. If you are not planning this, then I would use windows with a U-value of 0.9.

In my opinion, houses (from KFW70) today are already extremely well insulated. Whether you need 10 kWh/(m²*A) more or less heating energy hardly makes a difference in the annual final bill. The choice of heating system (e.g. heat pump with the highest possible COP) has a significantly greater impact on the costs.