Building Insulated Windows

[Zach Tomas]

Myself and LOML are getting ready to build a house. I realize that when most people say that they mean that their contracter is building one for them.

I mean we are building it ourselves - basement, foundation, framing, roof, the works.

She may be wanting some interesting windows and I'm not in the mood to pay some of the highway robbery prices. Now, building windows is no trick, but here it is hot in the summer and cold in the winter. I don't want to lose a bunch of energy through the glass.

Double pane windows are also nothing trick to put together. Shoot, even the mini-blinds between the panes type that are popular shouldn't be too difficult.

What I am concerned about is the fogging and water between the panes from condensation.

I have considered:

a. Assembling them inside a sealed box purged with nitrogen. (with gloves attached to arm holes)

b. Making the inside pane hinged for periodic opening/drying.

c. Attaching a fitting, tubing that runs to the attic, and tire valve at the end. Once a year, go to the attic and recharge the windows with nitrogen or CO2.

d. I am just nuts to begin with. (Make that "eccentric")

Thoughts?

-zach

[Wood Butcher]

I vote for the original "d" (parenthetically unmodified). ;~) The other options can be made functional, but with all the other work you'll need to do on the house - why bother?

Besides, factory built windows have a metallic coating in the inside of one of the glass sheets to reflect infrared wavelengths. This helps keep the heat in in the winter and out in the summer. This would be a bitch to try to duplicate yourself. Also factory windows are usually filled with argon or other inert gas which gives a bit better R value than N2 or CO2.

Art

[Wood Butcher]

It's the latter. A vacuum would be the ideal insulator but nobody has managed to engineer a window that is strong enough to keep the panes from flexing inward and touching and/or breaking.

Art

[Wood Butcher]

Jewberrywilcum.

[Pat Barber]

Aside from many building issues, and depending on where you live, many areas have VERY strick building codes with wind loads for windows.

In my area, windows require a wind load of over 100 mph. It is VERY doubtful you could build anything that meets or exceeds those specs in a reasonable amount of time and money.

Zach Tomas wrote:

Snipped parts about how easy it is to build windows.

[Charlie Spitzer]

you can purchase the window inserts (double/triple glass, sealed, argon filled) and just install them in your own window frames. call up a custom window place, not a distributor of installable windows.

regards, charlie cave creek, az

[Zach Tomas]

Welll, we live in one of the (for now) free parts of the world (rural Missouri) that still lets you build what you want as long as it doesn't mutilate random passersby.

I have a complete cabinet shop at my disposal (Ok, I admit to not having an edgebander) I would rather build than buy most things.

I just don't want water standing between the panes...

-zach

[Zach Tomas]

Well, now... Thanks for your vote of confidence.

Yup, I would rather use low-E glass. I don't know if it is available in raw form. No, I'm not planning on buiding a vacuum-vapor-metallic-deposit thingamajig.

Argon I can get. I didn't think about it having a better R value than nitrogen. What's up with that? Molecule size or something?

-zach

[Wood Butcher]

[snip]

That's a good question for a physical chemist, but I think you're on the right track (altho Ar doesn't form molecules). It could also be that Ar has lower mobility than N2 making convection currents slower. Or that Ar has a much lower specific heat [520 J/(Kg°K)] than N2 [1042].

Anybody know the real story?

Art

[Larry Jaques]

On Fri, 11 Jul 2003 18:07:19 GMT, "Jim Mc Namara" pixelated:

When I move din here, I had new dual-glazed windows put in. I would have done it myself but they wanted just $45 each to remove the old, install the new, seal, and flash them. They did it in 3 days andit would have taken me two weeks minimum. Anywho, the guy said that they are fairly well sealed and some came with argon inside, but most will leak eventually. Perhaps windows prices at 4x the cost of mine are better built, but I doubt that they remain fully sealed for decades. Mine have a lifetime guarantee from the installer, so I'm hoping his company outlives my needs. So far they're working fine.

Note to Zach: pay your money and let the PROs do it with a guarantee. My whole houseful of windows cost just $2,300, including one 6' slider and a 5x10 living room gaper. (My sister paid someone $11k in the SF Bay area, tho, but I know she got taken.)

- Yea, though I walk through the valley of Minwax, I shall stain no Cherry.

[PC]

About 10 years ago when we built our home I had over 50 Andersen windows installed. Now at least 45 of these need to be replaced because they have all leaked. Andersen apparently doesn't know how to seal glass reliably. The mechanism seems to be that the Argon between the panes leaks out, probably during periods of low barometric pressure and then as the pressure rises air, which is predominantly nitrogen, can't flow back into the void between the panes since nitrogen is a much larger molecule than the argon atom. This "pumping" over many years has left a substantial negative pressure. The consequence of this is that on low barometric pressure days Newton's rings are visible in many of the windows as the two panes approach one another and are separated by distances or only a few hundred nanometers. Interestingly the larger widows that Andersen custom made (some as large as 12 feet on a side) have not leaked. The problems are all with standard production doors and casement windows.

Unless you can achieve a perfect seal (it can be done but probably not at home) I'd urge you to back fill with dry nitrogen. Having a way to re-purge would not be a bad idea either. My vote would be to carefully look at window manufacturers and evaluate the quality of their product (Pella and Marvin come to mind) and buy the best you can find. The effort to make your own may be excessive for what they can be purchased for.

Phil

Zach Tomas wrote:

[Robert Bonomi]

Not more than about 80% so.

FORGET item (b) -- _any_ time you open it, all you'll be doing is letting in 'warm and damp' air.

There are two approaches: 1) *vent* the inter-pane space to the exterior. 2) build the pane assembly *air*tight* and *moisture*proof*, with appropriately low water-content in the inter-pane space.

The drawbacks to #1 are obvious.

#2 poses _significant_ construction difficulties.

"Thermo-pane"(TM) type windows have two layers of glass (with a vacuum or an inert gas -- nitrogen or argon -- between them), with the edge _sealed_ with a metallic (usually lead -- similar to stained-glass window construction) barrier.

Getting the seal air-tight, and that *stays* air-tight for many years, is a definitely 'non-trivial' job.

Anything that is _not_ absolutely "air tight" means that 'whatever' is in between the panes can get out, *and* that moisture can _get_in_.

Your (c) _might_ be the basis for "a plan". replace the 'once a year' refill idea with a continuous low-pressure supply.

[Robert Bonomi]

BZZZT! Vacuum panes exist. 'big' ones. We had 'em for 'sliding glass doors' opening onto a patio. 4' wide, 6'6" tall. installed in the mid 60's

[Wood Butcher]

They may have been advertised as such but simple physics says it ain't so.

Your door, at 48" x 78", has 3744 sq-in of surface area. At a very mild pressure differential of 1 psi there would be almost 2 tons of force trying to push the 2 panes together. At 14psi differential this force is about 26 tons. No window I know of will support this kind of force.

Show me the data. Otherwise I'm not a believer.

Art

[Mark & Shauna]

Aggreed, BZZZZZT yourself, there is no way to panels of glass (even small ones) could support the pressure of even the smallest vacuum. Go re-study your physics books, and call the manufacturer and ask for your money back as you were taken in by false advertising.

Mark

Wood Butcher wrote:

[Robert Bonomi]

Medium size home aquariums have glass panels supporting pressure differentials of several PSI.

Commercial aquariums -- e.g. the Chicago Aquarium have glass panels handling pressure differentials in excess of 10PSI.

You've got your 'knowledge'.

I've got first-hand experience.

Including a _catastrophic_ failure of one such panel. There was a substantial pressure differential between 'inside' and 'outside'. Glass shards went *everywhere*..

THIRTY YEARS after initial installation -- well, 24 for the one panel of 4 that was replaced, these panels weren't even 'cool' to the touch on the inside, when the outside temperature was 100F _lower_ outside than inside. (inside temp circa 70F, outside -30F, w/o wind-chill)

[Me]

That was going to be my suggestion. My house had new windows installed before I bought it. They are the energy efficient vinly frame windows, problem is the vinyl is flexible, all the frames have slightly bowed out of shape, some so much that the windows fell out of the tracks where they hinge open for cleaning so I had to unscrew the hinges and move them out a little and re mount to hold them in the track. The glass its self is still fine, double oane with an amuminum channel seperating them then they set them inside the vinyl frame. I have thought many times about cutting the vinyl off and building wood frames many times.

[Jeff Cochran]

Two issues. One is that the glass in commercial aquariums is quite thick, thicker than would be practical, or cost effective, in building a window. Second is that glass in an aquarium is a far cry from glass resisting a vacuum. In an aquarium, there is pressure on both sides, and the glass has to withstand the differential. In a vacuum, there's no pressure on one side.

The real proof it doesn't work is that no manufacturer makes a window with a vacuum between panes. You can bet they'd save the cost of the nitrogen or argon if it were economically possible.

Jeff

[Mark & Shauna]

Robert Bonomi wrote:

First of all, fish tanks have very thick glass. We had a 125 gallon which had glass almost 1/2" thick. Additionally the pressures in home fish tanks are trivial compared to those which would be exerted on that of a fish tank. Did you read the other post which did the math showing you that you would need a piece of glass which could support 26 tons? So you are telling us the glass in your sliding glass doors could be laid flat and support 52,000 pounds without bending/breaking. You now bring up aquarium glass in commercial applications. In case you didnt see it while you were there, most aquariums have a sample of the glass they use and it is of no compare to anything relavent to this thread. It has to not only be able to withstand the weight of the water but a potential strike from a large occupant. The cool inside is often the case with good double pane panels. The "catastrophic failure" you wittnessed was because all glass which comes with in a given distance of the floor of structure, and door glass, has to be saftey glass, usually tempered. This means that in the cooling process of manufacturing the glass they tension the outer skin of the glass. What this does is put the glass itself under enourmous tension. This tension is there so that when the panel is bent to the point of breaking the tension causes it to shatter to millions of tiny pieces rather than creating shards. Its a very wild process to watch for sure and almost seems like the glass "explodes". Very loud bang, etc. It is not an explosion, its the way the glass is designed to fail for your saftey. It has absolutely nothing to do with the contents, or lack there of, inside the panel. Again, you could simply research this with any window manufacturer, or choose to do the physics your self (most has already been done for you) and find out that the vacuum issue is mute.

Ciao... Mark

[Jeff Cochran]

Obviously never been in a lab and created a vacuum with a flat panel... :)

Pressure differential isn't simple x-y math. And the closer you get to a true vacuum the less predictable the differential forces actually are. To withstand pressure differential, and 15 PSI is actually quite a strong differential for a flat glass panel of window pane thickness, requires a structural design which can distribute the force throughout the material. Hence the fact that most vacuum containers are rounded or globes.

But this isn't a physics forum, and I'll never convince you here.

Jeff