>>and the voids are frequently filled with noble gasses like Argon for improved insulation.

How long is such a window rated for? Surely the gas will eventually leak out?

Not really a problem one would be aware of. Double glazing is the default since 50 years at least in Germany, so the manufacturing processes are quite good.

Still, leakages happen, you recognize that usually by water/steam between the two glass panes. If the windows aren't to old you can just switch out the glass leaving the plastic frames. If they're older (30 yrs) it's more economical to switch out glass and frames.

Almost all my double glazed windows have now failed and I'm looking at replacements, but my fear is that the failures are due to the amount of vibrations this house gets (I'm close to a busy road, every time a lorry goes past I can feel it in some rooms).

From what I can find, the leakage is estimated at < 1% per year. This (German) discussion references and quotes the (German) industry standard DIN EN 1279-3.

https://www.haustechnikdialog.de/Forum/t/65875/Haltbarkeit-A...

Leakage rate is ~1% per year. However the gas isn’t so important you need to replace the window as argon is only up to 16% better than air.

It’s worth it to manufacture windows like this, but unless you’re in the arctic circle I wouldn’t worry about the difference.

There’s been so many window manufacturer lawsuits over this issue that my guess is a manufacturing defect.

Properly constructed, I think these windows are expected to have a useful lifespan of at least 20-30 years. I think the heavier gasses are less likely to leak, so long as the window is kept intact and undamaged.

I'd expect the insulating properties of a gas at normal temperatures and pressures to depend only on the molecular mass. That's 40 for argon, and 28 for nitrogen. This web page (https://www.pressglass.com/noble-gases-and-thermal-insulatio...) says the thermal conductivities are 0,026 W/(mK) for air and 0,018 W/(mK) for argon. 26/18 is about 1.44; 40/28 is about 1.43. So perhaps the conductivity is inversely proportional to the molecular mass? In that's true then it's not a "noble" gas you want for improved insulation, but a dense gas (so not helium). You should be using tungsten hexafluoride! OK, not really: see https://en.wikipedia.org/wiki/Tungsten_hexafluoride for why not.

The heat capacity of the gas depends on both mass and molecular structure. Atoms like argon have no structure, but molecules like O2 and N2 carry extra heat energy in their vibrating bond, so they have more heat capacity per unit mass.

That's a good point. Perhaps the result of that argon/nitrogen comparison was a coincidence, or perhaps heat capacity doesn't much affect thermal conductivity.

Here's an argument that heat capacity shouldn't affect thermal conductivity in a solid: imagine a block of material with a smooth temperature gradient through it and the temperature at any point remaining constant, so there is heat flowing through it. Now imagine you have some tiny beads of some other material with a super-high heat capacity. Distribute those beads throughout the block of material, preheating each bead to the correct local temperature before inserting it. Then intuitively it seems that neither any local temperature nor the rate of flow of heat through the block should change much. Yet the heat capacity of the new composite material is significantly higher than that of the original material. Does that argument make sense? I did physics at school but not since then!

Yes, I don't think they're strongly related in a solid.

But in a gas, heat transfer is mostly driven by convection. Gas near the hot surface heats up, rises, moves to the cold surface, falls, and repeats. So what matters is the specific heat capacity * the flow rate between hot and cold surfaces.

Thanks for that explanation. So the "thermal conductivities" I quoted above, if they don't take account of convection, are perhaps not even particularly relevant. The advantage of argon over nitrogen might be greater than those numbers suggest?

I'm not exactly sure how they choose which particular gas to use, but I'm sure the lighter gasses will leak more easily.

Conceptually, it's like a thermos bottle, and you'd think that you would want a vacuum, but apparently that's hard to keep intact on windows, so a noble gas between the layers works better.

Yes, but not any old noble gas. Helium and neon, for example, have higher thermal conductivities than nitrogen. So it seems like argon is better for the job as well as being cheaper.

(While every noble gas has roughly the same heat capacity by mole/volume. Perhaps some CFCs would have been even better for insulation, but bad for the ozone layer, of course, and rightly banned?)

That probably depends on where you are. Here in Amsterdam, our triple glazing is made out of all actual glass. In our house it’s made out of four 6-mm sheets of glass actually. So one double sheet that’s a sandwich with a glued layer of foil in between (like a windshield), used as a security component either on the outside (anti break-in) or on the upper floors on the inside as a way to prevent falling through the window.

Having more layers of actual glass helps with sound insulation also, probably more of a concern in Amsterdam than in Norway.

6mm sounds very thick?

Probably meant 6 mil (1mil = 1 thousandth of an inch), since this is a typical non-metric measure of sheet thickness (metal, glass, plastic).

Yeah, I'm sure it does depend on where you are.

For the nearly eight years that my wife and I lived in Brussels, Belgium, we lived in an old house (rented) that was built around 1910, and so we didn't have even double glazing, although we did have French Doors, and we had custom-made screens that had to be manually placed into the windows and then pinned in place with a nail instead of always attached to the outside. So, I don't have much knowledge of what current European building standards are in this space.

I do prefer the German-style double-opening windows that I saw in the house my sister-in-law was renting near Spangdalem AFB, along with the Rolladen that they had installed. But again, that was a rental in an older home.

I have been watching Laura Kampf and her "Haus Lise Lotte" project on YouTube, but again that's a 120 year old house, and they haven't gotten to replacing the windows yet.

Any suggestions for an English language channel where I could learn more about current European building standards, maybe something like Matt Risinger's "Build Show" for US building standards that I've been watching on YouTube?

It's all about the UK but Grand Designs often features builds that have technology and equipment from the continent.

Somehow I’d thought the voids were usually evacuated but that doesn’t really make sense with the pressure involved. Apparently it is possible to have a vacuum inside but uncommon and harder to manufacture (and you need support pillars to separate the panes). https://www.glassonweb.com/article/vacuum-insulating-glass-p...

You'd still have radiative heat transfer, even if there is a vacuum between the panes. For a given budget, you're probably better off adding more regular panes.

Aren’t new windows often coated with something opaque to IR, that way they keep heat in during winter and don’t heat up like a greenhouse in the summer?

Those are low-emissivity coatings. Very effective in reducing radiative heat transfer. This is why the glass in a vacuum flask is silvered: metals have low emissivity. These coatings aim to have low IR emissivity while still allowing visible light through (IR light gets reflected, instead of absorbed/emitted).

My point was only that a vacuum gap is still not a perfect insulator, so it's an economic trade-off.