Double or triple glazing in new buildings - triple glazing allegedly unnecessary expense

Hello everyone,

the window seller/advisor responded to our request to install triple glazing with a UW=0.6 in a new building (KFW60 level) by recommending to rather use double glazing with a UW=0.81 value.
The additional costs for the almost 17 doors, windows, and floor-to-ceiling windows amount to a total of 3,000 EUR.
He then calculated for us that with triple glazing there is less thermal radiation (which is understandable thanks to light refraction, etc.), yet I am surprised that it supposedly wouldn’t be worthwhile at all. On the internet, I found a break-even of about 10 years for the additional costs of triple glazing.

How do you assess this?

Thanks!

Is KFW55 not standard and also mandatory by now? I would definitely tend to go for triple-glazed windows. In old houses today, windows are, as far as I know, one of the huge thermal bridges. I wouldn’t save there.

Isn’t KFW55 now standard and also mandatory?

From 2023. Kfw 60 has never existed.

The window seller/advisor recommended, in response to our request for a new building (KFW60 level) to install triple glazing with Uw=0.6, to rather install only double glazing with a Uw=0.81 value.

Question: How does the advisor arrive at a Uw value of 0.81 with double glazing? If he manages that, then double glazing can also be used without hesitation. I have no idea how that works. Many triple-glazed windows have worse values.

It really depends a lot on where the sun actually shines in winter and how much. The window salesman surely hasn't calculated that exactly just like that. If you go into detail, you can also include points like comfort from radiant heat; 2-pane windows radiate colder than 3-pane windows, so you have to heat the room to a higher temperature to feel the same. You can get lost in details if you want. Or you can factor in the interest on the 3,000 and compare it to possible developments in energy costs, etc. etc. But it simply makes little sense to want to save 3,000€ here. Pure additional heating costs will surely only be around 50€ per year at a flow temperature... If you have to watch every euro, you can certainly save that, but then you should also consider whether all of that is good if you have to watch 3,000€.

I rather assume it is about the Ug value...

Ok, ok, something definitely got mixed up with the Uw and Ug values, sorry about that.

I deliberately wrote the level of KFW60 because the energy consumption of the house is precisely at that level. Let's put aside the canceled KFW subsidy, which we wouldn't have gotten/will not get anyway.

And no: it was not about the last 3,000 EUR. On the contrary: I was actually fully convinced to go for the triple glazing, but the consultant himself then said on his own that it actually doesn’t bring much overall. I was quite surprised by that myself. I will have the technical data sent to me again to have it assessed more precisely.

The 4 large floor-to-ceiling elements are definitely facing south, but as you already wrote: the sun doesn’t seem to shine every day!

The savings of 50 EUR per year on heating costs was roughly how he formulated it compared to triple glazing. Hence his suggestion on whether it might be better to spend that money on something else.