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How much energy does it take to make a double glazed unit?

Peter wrote:

they are cheaper to make

True, but with smaller windows one needs larger walls which ain’t for free either especially if you figure in exterior insulation.

they lose less heat through the windows, so building efficiency compliance is easier to meet

A good window loses many times less heat than a bad wall. When the days get shorter in fall I regularly get condensation on my house’s windows. But at the outside! Two months later and they are going to get frosted. The heat loss of such a window is still several times more than that of a good wall but only at night. A south facing modern window loses less heat at night than it lets in at daytime, even on a winters day. But no gain no pain: This is even more true in summer so some kind of (exterior) window shades are a must.

in the countryside, the dickhead planners don’t like big windows due to “light pollution” (no use telling them there are c-u-r-t-a-i-n-s)

Is this really a thing? I have seen that term applied to street lighting or excessive exterior lighting for (usually commercial) buildings but never to light coming out of the windows of residential houses.

large windows aren’t “English vernacular” style

Then you have to put the bling on the inside and the outside.

A friend of mine in Germany has recently built a super high tech low energy house.

This is getting more and more common. Last year my total (natural) gas bill for my single family home was less than 250€. Gas prices are currently skyrocketting but I couldn’t care less. There are even housing developments where the houses must produce more energy than they consume. I believe the trend is not unique to Germany and similar houses are being built all over Europe and especially Scandinavia.

EDQH, Germany

Graham wrote:

This is where you tell me that the distinction seems odd because the latter have not been seen in Norway for fifty years!

That’s about right I remember we used to have “double-windows”. The outer window open outward and the inner window opens inward. In the summer we removed the inner window altogether and put it back again in the fall. Usually each window consisted of 4 or 6 smaller windows (panes?), and each window had one single layer of glass.

Then windows with double glass became standard, about 50 years ago, probably earlier for new houses Today, all new houses have triple glass. My house has only 2. They don’t recommend changing older houses from 2 to 3. The reason is that before 1990, double glass had a “U-value” of 3. Modern double glass has a “U-value” of 1.1 while modern triple glass has 0.8. The added cost of going to (new) triple glass instead of (new) double glass will not be payed back even in 50 years, because the walls also would need better insulation.

IMO old windows were much nicer. When it was real cold, they used to condense and freeze, and create a real, authentic “Christmassy” look and feel that is was fun melt holes in with your fingers. Today one has to use spray paint to create the same effect, and it’s utterly fake anyway. Electricity is cheap, wood is free and carbon neutral bio-fuel (if you bother to cut it yourself). Tight houses creates asthma among children anyway. It’s mostly hysteria with no real benefits of any kind, except new windows are large of course.


If your windows only last for 20 years, maybe you should change the window maker? Or don’t polish it with whatever you use? Is this house usually exposed to sand storms? It sounds weird to me.

And yes, here in Germany in practically any new or replace installation triple glass windows are used. They give a 20 years warranty on new windows, so it really shouldn’t have nothing in that time.

Windows come quite expensive, so nobody really would accept windows which only last 20 years.

Expert tip. You could buy a triple glass window and whenever the outer pane gets blind, just kick out the outer pane and continue with two panes

Last Edited by UdoR at 07 Oct 09:59

How many companies are still around after 20 years – in any business especially “property improvements”? Practically nobody. Many sell extended warranties but many of these are with fake insurance companies (I’ve had a few of those). So a 20 year warranty is worthless.

Yes; insulation and heat recovery is a challenge when you also want lots of fresh air. It can be done but is very expensive, so normally the price paid is a low rate of air exchange.

Shoreham EGKA, United Kingdom

Peter wrote:

How many companies are still around after 20 years

If you look at the window market leaders in Germany (Weru, Schüko, Velux (ok, that’s Danish), Hapa) the answer is: All of them. They are all around since at least the Mid 60ies – with Weru going back into the 19th century.

This might be one of the reasons for different standards across different countries: In Germany the vast majority of windows is industrially manufactures with the local glaziers being just installation shops. In other countries they do much more dezentral manufacturing from raw sheet glass….


Sure, but these are manufacturers, not installers. Is a German mfg liable for the whole finished installation? For 20 years, and where the installer used steel screws which rusted and punctured the seal. Or the window frame is under stress and cracked the sealed unit. I don’t believe that will work.

Shoreham EGKA, United Kingdom

Window warranties are not worth the paper they are written on. Look at the list of exclusions, plus the potential for installation problems as pointed out by Peter.

I occasionally investigate glass defects on very expensive panes (on behalf of insurers). Unfortunately, defects are generally not covered by insurance and I have yet to see a manufacturer cough up.

As many of these are actually manufacturing defects, e.g. nickel sulfide inclusions, I believe that they should be covered by a warranty, but this has not been my experience.

Last Edited by Canuck at 07 Oct 12:42
Sans aircraft at the moment :-(, United Kingdom
If your windows only last for 20 years, maybe you should change the window maker? Or don’t polish it with whatever you use? Is this house usually exposed to sand storms? It sounds weird to me.

Double glazing units become “foggy” if the seal between the panes and the spacers fails. These spacers are filled with silica gel or somesuch and keep the gas between the panes bone dry. And with the seals intact, there is no way for moisture to get in after installation.

When the seals fail, some gas is pushed out when the window heats up and outside air is pushed in when it cools down again. Slowly, moisture gets in and when the silica gel is saturated, it starts condensing on the inside of the panes.

There are temporary fixes which all require holes in the panes, but normally the units have to be replaced.

20-30 years seems to be the limit. but I have seen failures after 4-5 years, mostly caused by the installation (e.g., no proper spacers between the frames and the units)

Last Edited by Cobalt at 08 Oct 00:35
Biggin Hill

Cobalt wrote:

20-30 years seems to be the limit

I thought windows are expected to last for 50-60 years, which they do IMO. Leakage is a production fault.


Cobalt wrote:

20-30 years seems to be the limit.

My home was built in the mid 90ies and has a lot of large glass areas (>100 sqm in total of double glazed windows). According to your statement the windows should be end of lifecycle.
When I bought it about 10 years ago, all but one 2,5×1m segments still was original since built (I don’t know why this segment had to be replaced). Since then I had to replace one other segment (cracked due to thermal stress – I made should not have placed the bbq directly in front of this window ;-)) and one other got a bit hazy. So more than 95% of the windows are still perfectly fine after 30 years.

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