Cracked inner panel of dual pane glass (Caused by window film or cellular shades w/ tracks?)

[jay]

I have a room in my house (I live in the Northeast) with two dual-pane windows next to each other (separate individual windows within the same frame).

Today sometime toward the end of the afternoon, one of the inner panels of one of the windows developed a big crack. This particular room has a problem in which, since it faces the south, the room tends to get warmer than other rooms in the house on sunny days. This is due to heat from the sun making its' way through the window.

I had installed tinted window film on the inside of the glass about 2 months ago. This is the kind that adheres via static cling. The manufacturer recommended against putting it on the inside of double-pane windows, but I tried it anyway, since, frankly, this film wasn't even very effective, but is CLAIMED to have a summer shading coefficient of .67 which isn't all that great a spec to begin with. (I also figured that since the windows are 20 years old, the seal was likely shot and there would not be much risk of them "exploding")

About 1 month ago, since the window film alone did NOT help much in keeping the heat from getting into the room, I installed a double-cellular honeycomb room darkening shade that has side tracks so that the sides are virtually sealed. This did seem help a little in keeping heat from getting into the room, but tends to trap warm air between the shade and the window.

Again, the combination of both the window film and the shade-with-side-tracks seemed to help a little in reducing the heat, but now today all of a sudden I have the crack in the inner pane of one of the windows. For this reason I have removed the window film because it is a strong suspect (simply because the manufacturer's warning "told me so" ).

Do you think it was the window film alone that was the cause of the cracked glass, or could it have been due to the the cellular shade-with-side-tracks? Do you recommend I remove the side-tracks from the shade to avoid another crack, and just accept the fact that this room gets hotter than the others? Could the crack have been a wild anomaly not caused by the film or the shade?

Thanks,

J.

[Roger T.]

. The manufacturer

Therein lies the problem.

*follow manufacturers' recommendations*

Reflective film reflects a large amount of radiant heat directly into the hollow between the windows, overheating both panes. That is why all film manufacturers are loathe to put them on double glazing. Likely as not simple heat caused thermal crack; not necessarily expansion/explosion of the center gas, as you suspect. The added insulated shade may have exacerbated the heating effect, especially on the inner pane. So you had trapped heat heating both panes, and the shade adding extra heat to the inner pane.

[m Ransley]

The combination of the 2, Manufacturer said not to use the film inside, keep the shades. They provide probably R3 , good at night to keep heat in.

[jay]

If the window film was the cause, and I agree it could be, it certainly took a while (two months) for it to happen, with a lot of sunny days during that time.

Ok, now that I've removed the window film, it sounds like I should probably remove the side tracks from the insulated shade and just live with the not-so-comfortable heat problem, or do you think just removing the window film might be enough to prevent future cracks?

Is there a special glass panel that would prevent heat from getting into the room in the first place (while still conforming to condominium standards)? Putting up an awning isn't an option since it's a condo.

Thanks,

J.

[jay]

The shades have side tracks which seal the gaps on the sides of the shades. If you think I should remove the tracks, let me know.

Thanks,

J.

[Colbyt]

shade-with-side-tracks?

For this reason I have removed the window film because it is a strong suspect (simply because the manufacturer's warning "told me so" ).

I suspect it was the combination of the two. I doubt that the shade alone would have caused this problem. We routinely install them in skylights, with the side rails and any solar orientation. I have never had a callback.

Since you are going to need to replace the window unit you might want to look at some of the units with the low-e ratings. I don't have a clue as to what is available but I know they are out there.

Colbyt

[JerryMouse]

Heat move by three vectors: Radiation, Conduction, or Convection.

The double-glass windows attempt to reduce "conduction" (i.e., the outer pane gets cold/hot but does not transmit that condition to the inner glass. Double-glass windows do nothing about radiation.

Reflective film is a radiation barrier. So, here's what happened.

It's cold outside. The outer pane gets cold. The cold is transferred, via conduction, to the air between the panes. This air, in turn, cools the outermost layer of the inner pane's glass.

Meanwhile, radiation from the sun is heating the reflective film. It, in turn, heats the innermost part of the inner pane.

Inner pane is now hot on one side, cold on the other.

Bang.

[jay]

I agree this is likely what happened, but why did it happen today and not any other with the last two months? Today was a perfectly sunny day, and in the low 30s. There have been perfectly sunny days much colder (teens) and also there have been perfectcly sunny days much warmer (50s) and yet today was the day this crack happened. During this time period (two months) the sun was never obscured even at the very beginning of winter. Just wondering why today?

J.

[jay]

What I mean was that the sun was never obscured BY TREES on a sunny day, even at the winter solstace.

J.

[m Ransley]

The sun has been getting stronger every day in the northern hemisphere since apx dec 20th, plus your shades insulate. What shades did you get, what is their R value.

[Joseph Meehan]

Well you learned the hard way. Follow the instructions.

The good part is you can now replace that pane (you are going to need to replace it unless you like cloudy glass) with a new low-e pane that will likely go a long way towards reducing that heat gain, and will also help keep the heat in during the winter. It will cost a little more, but based on my personal use, it will be well worth it.

Don't worry about the shades, they did not cause the problem.

[Goedjn]

Your real problem is that you live in a condo. How about shutters, are they allowed? Make your awning/shutters out of solar panels, and then when the condo-board complains, tell them that state law prohibits them from interfering with your alternative energy solutions. If that's not true, lie. Sell the condo and buy a shack somewhere where you actually have rights to your own property, and you will be happier and more comfortable.

--Goedjn

[Goedjn]

Fatigue due to thermal stresses in glass is cumulative. This is about pyrex, but the same principles apply:

[jay]

I have Comfortrack room-darkening double-cellular honeycomb shades. These shades have side tracks. Today it's another very sunny day out, and, if I leave these shades pulled down for a while and then pull them back up and then I immediately touch the window glass with my hand, the window glass is hot, and is VERY hot as you get toward the top 1/3 of the panel. I can't even keep my hand on the glass on the top 1/3 of the panel.

The glass never got that hot when using the levelor aluminum blinds which were outside mounted

The reason I got these shades was to help keep heat from getting into the room. Do you think I'm still risking another cracked panel by continuing to use thse insulated shades even though I just removed the tinted window film?

Thanks,

J.

[jay]

Ok, so I guess this means the other panel in the adjacent window could be on the verge of damage, right?

Even though I removed the window film, I'm thinking that perhaps the double-cell honeycomb shades (with side tracks) are a big part of the cause. Today it's sunny out, and if I pull down the shades for a while, and then lift them up and put my hand on the window glass it gets hot, and VERY hot toward the top 1/3 of the glass (can't even keep my hand on the glass)

The glass did NOT get that hot when using the levelor aluminum blinds that came with the condo. The glass got warm but not hot.

Do you think I'm risking another crack by continuing to use the insulated shades, given that they cause the glass to get very hot?

One key point: these shades have side tracks to seal the edges, which causes hot air to get trapped between the shade and the glass.

My goal, when getting the shades was to prevent heat from getting into the room. This "worked" but not I have a cracked glass panel. I could remove the side-tracks, or go back to using leveler blinds, but that would mean I'll have to live with the room itself getting too warm.

Again, do you think it's okay to use the shades as is, even though they are causing the glass to get very hot? I find it hard to believe the window film alone was the cause of the crack. The shades have to be LEAST 50% of the cause. (the tinted window film was not very effective at keeping heat out of the room)

J.

[m Ransley]

Who makes Comfortrack, I could not find them. Ive seen some very high R shades avalaible R 4.5. Call your shade Co and Pella or Anderson. If your window tint was dark it held in more heat than you realise. I would think glass if it expands slowly will be ok, that yours expanded to fast when the sun came up. I dought it is the shades but to hot to touch is reason for concern.

[jay]

Comfortex makes comfortrack. I'm not sure the exact R value.

It happened toward the end of the afternoon, likely as it got cooler outside.

J.

[Matt]

It's really hard to say exactly what caused it.

I think you need to replace the windows with EXACTLY what was there before, and conduct more experiments.

I'd say if you do this about 50 times, you should have a definite cause/effect relationship nailed down. Please do post back with the results.

[Charles Spitzer]

it is always better to prevent the heat from getting inside. once it's inside, it has nowhere else to go and you have to pay to move it outside. use outside shades, trees, or even sunscreen on the outside of the window to solve your problem.

[Gino]

Bad thing to do. NEVER put tinted film on the inside of sealed units. The film instructions should have made that clear.