ᐅ Double or triple glazing in new construction – triple glazing allegedly an unnecessary expense
Created on: 23 Sep 2022 09:54
S
Smeagol
Hello everyone,
The window salesperson/advisor recommended using double glazing with a U-value of 0.81 instead of triple glazing with a U-value of 0.6 for our new build at KFW60 standard.
The additional cost for the nearly 17 windows and patio doors totals around 3,000 EUR.
They explained that triple glazing reduces solar heat gain (which makes sense due to light refraction and so on), but still suggested that the extra expense might not be worth it. Online, I found a break-even point of about 10 years for the additional cost of triple glazing.
What’s your assessment?
Thanks!
The window salesperson/advisor recommended using double glazing with a U-value of 0.81 instead of triple glazing with a U-value of 0.6 for our new build at KFW60 standard.
The additional cost for the nearly 17 windows and patio doors totals around 3,000 EUR.
They explained that triple glazing reduces solar heat gain (which makes sense due to light refraction and so on), but still suggested that the extra expense might not be worth it. Online, I found a break-even point of about 10 years for the additional cost of triple glazing.
What’s your assessment?
Thanks!
11ant schrieb:
I consider the idea of double glazing on the south side (which might also make sliding doors easier) to be quite reasonable, but this should be assessed on a case-by-case basis.
I see it differently; see also “Are three window panes better than two?” (not linkable here, but easily searchable by the title). I also recommend the related post on the topic of “warm edge,” which…
… is not yet mentioned here. The term is probably also a registered trademark – I have not researched how far the concept is patented. However, I do not see it as a fundamentally new invention.Swissspacer = a well-known manufacturer in professional circles for thermally improved insulating glass edge seals = warm edge = definitely worthwhile = significantly less condensation at the glass edge and energy savings = with only minor additional costs. Today, I would always choose windows with triple glazing and a Ug-value of 0.6.
profil65 schrieb:
Today, I would always choose windows with triple glazing and a Ug value of 0.6. I would also go for triple glazing. It seems to be the standard nowadays, I think.
We ordered our windows from a window dealer we know in Poland. They are aluminum windows from Aliplast (a Belgian manufacturer). The Polish dealer naturally included triple glazing for all windows (Ug value 0.5!), along with Swissspacer warm edge technology. The installation will follow the RAL guidelines using “warm” window sills and Illbruck compressible sealing tapes. All floor-to-ceiling windows will have a Purenit base instead of a doubled frame.
I thought that if this level of professionalism is standard in Poland, it has long been the case in Germany as well...
You can calculate the numbers yourself.
To simplify, we only compare the Ug value (the thermal transmittance of the glass alone). The heat loss through the window area is the product of the area, temperature difference, and U-value.
Five large double windows (e.g., patio doors), each 4 m² (43 ft²), give a total glass area of 20 m² (215 ft²).
With 20°C (68°F) inside and -5°C (23°F) outside, the temperature difference is 25 K (45°F).
U-values are given (as mentioned, we simplify by considering only the losses through the glass area, so just the Ug).
20 m² * 25 K * 0.6 W/(m²·K) = 300 W
or 20 m² glass area * 25 K * 1.1 W/(m²·K) = 550 W.
This 250-watt difference means you need to provide more heating energy; over a constant 24-hour day at -5°C (23°F), that is 250 W * 24 h = 6000 Wh = 6 kWh.
Of course, the temperature difference is not constant, but you can look up the cumulative temperature difference depending on your location (search for heating degree days, "DegreeDays-Germany.xlsx" or similar). Let’s take a typical German value of 3500 K·d = 84,000 K·h.
Then, for the 20 m² glass area, the total heat loss over the year at Ug=0.6 is 1008 kWh and at Ug=1.1 is 1848 kWh, which is 840 kWh more. How much do those additional 840 kWh of heating energy cost you? It’s a relatively simple calculation with gas, but it can be trickier with heat pumps because their efficiency can vary significantly depending on outdoor temperature.
With your location (warmer by the sea, colder in upland areas) and window area, you can calculate this yourself; it’s sufficient to use a Ug difference of 0.5.
However, the 50 € you mentioned is certainly far too low—even with pre-crisis gas prices, it wouldn’t add up.
The sales advisor/consultant probably still needs to sell a few double-glazed windows.
Best regards
To simplify, we only compare the Ug value (the thermal transmittance of the glass alone). The heat loss through the window area is the product of the area, temperature difference, and U-value.
Five large double windows (e.g., patio doors), each 4 m² (43 ft²), give a total glass area of 20 m² (215 ft²).
With 20°C (68°F) inside and -5°C (23°F) outside, the temperature difference is 25 K (45°F).
U-values are given (as mentioned, we simplify by considering only the losses through the glass area, so just the Ug).
20 m² * 25 K * 0.6 W/(m²·K) = 300 W
or 20 m² glass area * 25 K * 1.1 W/(m²·K) = 550 W.
This 250-watt difference means you need to provide more heating energy; over a constant 24-hour day at -5°C (23°F), that is 250 W * 24 h = 6000 Wh = 6 kWh.
Of course, the temperature difference is not constant, but you can look up the cumulative temperature difference depending on your location (search for heating degree days, "DegreeDays-Germany.xlsx" or similar). Let’s take a typical German value of 3500 K·d = 84,000 K·h.
Then, for the 20 m² glass area, the total heat loss over the year at Ug=0.6 is 1008 kWh and at Ug=1.1 is 1848 kWh, which is 840 kWh more. How much do those additional 840 kWh of heating energy cost you? It’s a relatively simple calculation with gas, but it can be trickier with heat pumps because their efficiency can vary significantly depending on outdoor temperature.
With your location (warmer by the sea, colder in upland areas) and window area, you can calculate this yourself; it’s sufficient to use a Ug difference of 0.5.
However, the 50 € you mentioned is certainly far too low—even with pre-crisis gas prices, it wouldn’t add up.
The sales advisor/consultant probably still needs to sell a few double-glazed windows.
Best regards
Winniefred27 Sep 2022 07:47I wouldn’t cut corners on the glazing either; I think you made the right decision there.
In our older house, we replaced the double-glazed windows with high-quality triple glazing, and the difference is significant. Only in the attic did we install new double-glazed roof windows. Since we only sleep up there and have shutters installed to manage heat and cold, that is sufficient.
On the ground floor, the last three new windows will finally be installed soon, and I’m looking forward to it because it really makes a difference. I am referring here to double-glazed windows from the 1990s, but I believe that triple glazing simply offers more, even or especially today.
In our older house, we replaced the double-glazed windows with high-quality triple glazing, and the difference is significant. Only in the attic did we install new double-glazed roof windows. Since we only sleep up there and have shutters installed to manage heat and cold, that is sufficient.
On the ground floor, the last three new windows will finally be installed soon, and I’m looking forward to it because it really makes a difference. I am referring here to double-glazed windows from the 1990s, but I believe that triple glazing simply offers more, even or especially today.
Winniefred schrieb:
Although I’m talking here about double-glazed windows from the 1990s, I believe that triple glazing simply offers more benefits, even or especially today. There are very different types of glass, so double glazing is not necessarily worse than triple glazing (for trademark reasons, I am temporarily not providing links to my external posts).
https://www.instagram.com/11antgmxde/
https://www.linkedin.com/company/bauen-jetzt/
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