ᐅ Window glass U-value 0.7 W/m²·K vs. 0.75 W/m²·K

Hello dear community,

A clueless person going astray.

I am currently considering whether it is really worth upgrading the quality of the window materials. I know this is somewhat speculative. We have quite a few floor-to-ceiling window units. The entire south-facing side is almost fully glazed. Wall construction is 24 cm (9.5 inches) brick with 18 cm (7 inches) external thermal insulation composite system (ETICS) – also a matter of personal preference, but not the topic here.

We are planning to use the Brügmann Bluevolution 82 profile. The additional cost would be about 1500 euros for all the windows. That means I would need to save roughly 80 euros per year, assuming a service life of about 20 years. The extra cost seems reasonable; however, we are hesitating a bit because we have already placed some orders... 500 euros, 1000 euros here and there...

Gradually, it adds up...

What is your opinion? Would the effort be worthwhile? Or are my standard windows already performing well enough?

Good luck

P.S. If there is interest, we can also discuss window insulation in general in this thread.

Oops, the heading is incorrect; it should of course be 0.50 W/m²K.

How does the overall U-value of the entire window change? Then this consideration might make more sense.

The window size changes from 0.89 to 0.76 for the standard window.

However, since we have many large glass surfaces (many floor-to-ceiling elements 2.50m (8 ft 2 in)), I thought the glass value would actually be more meaningful.

Good luck

Fanta

So you save 0.13 W per square meter and per 1° temperature difference. You can roughly calculate how much heat energy is lost based on the average temperatures during the heating months, for example per day at around 0 degrees outside: an average indoor-outdoor difference of 20°C (36°F) results in 20 * 0.13 W/m²K = 2.6 W per square meter, which means per day 2.6 W * 24 h = 62.4 Wh = 0.0624 kWh per square meter. With about (you save by having information!) 15 m² (162 ft²), that equals 0.936 kWh of heat energy. With an efficient heat pump, that might use about 0.2 to 0.25 kWh of electricity, roughly 7 cents for the day. If each of the 150 days in the heating period is that cold, it totals about 10 euros per year. However, I don’t know your indoor temperature or all other data, so this estimate is only rough.

So you can estimate savings based on temperatures in your region over the past years.

Whether comfort actually improves due to less cold near the windows, I would doubt at these values. Usually, a thicker frame brings much more improvement than just better glazing.

Thank you very much for your detailed response, Saurus!!

Sorry if I was a bit sparse with information. I thought the data was already sufficient, but of course, a lot depends on the heating system and the rest of the insulation.

You definitely helped me a lot in making my decision.

If I should add any information for others, just let me know briefly which data I should include.

I will probably stick with the 0.7 glass since the savings seem too small to me.

Best regards

Fanta