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"
grin).

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.

.. The manufacturer
recommended against putting it on the inside of double-pane windows, but I
tried it anyway,

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.

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.

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.

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.

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.

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.

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.

jay wrote:
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.

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.

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.

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.

During this time period (two months) the
sun was never obscured even at the very beginning of winter. Just wondering
why today?

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

J.

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.

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.

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

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?

Fatigue due to thermal stresses in glass is cumulative.
This is about pyrex, but the same principles apply:
http://www.newton.dep.anl.gov/askasc...9/eng99265.htm

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.

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

Well, today is another very sunny day. When these insulated shades (with
side tracks) are pulled down for a while, and then I pull them up and touch
the window glass, the glass is hot, and is VERY hot toward the top 1/3 of
the panel (can't even keep my hand on the panel).

The glass did not get that hot when using the outside mounted levelor
aluminum blinds that were there when I bought the condo.

Do you still think the shades have nothing to do with it even though they
cause the glass to get VERY hot?

J.

Fatigue due to thermal stresses in glass is cumulative.
This is about pyrex, but the same principles apply:
http://www.newton.dep.anl.gov/askasc...9/eng99265.htm

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.

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.

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.

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.

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.

"jay" wrote in message
news:un9Md.10893$8a6.5021@trndny09...
Fatigue due to thermal stresses in glass is cumulative.
This is about pyrex, but the same principles apply:
http://www.newton.dep.anl.gov/askasc...9/eng99265.htm

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.

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.

On Wed, 02 Feb 2005 18:56:26 GMT, "jay" wrote:

Fatigue due to thermal stresses in glass is cumulative.
This is about pyrex, but the same principles apply:
http://www.newton.dep.anl.gov/askasc...9/eng99265.htm

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)


I suspect that the combination of the IR-resistant film and
the shades was more than additively worse than either by
themselves, because the shade tries to send heat back out
through the window, and the low-E film was fighting against
you. If the shades are actually any good at reflecting
radiated heat, then you don't WANT low-E film, you want
the light to come in, bounce off the shades, and bounce
back out, without even noticing that there was a window there.

Do you have window screens on the outside of the window?
Those would help, and you should get enough airflow through
the screen to keep heat buildup from being a problem.

Do you have window screens on the outside of the window?
Those would help, and you should get enough airflow through
the screen to keep heat buildup from being a problem.

Even today (with no window film) the shades alone caused the window to get
so hot I could not keep my hand on it.

The window screens were on the inside (between the shade and the window).
Today I don't have the screens installed, since I had to remove them to get
rid of the window film, and will install them again after I have new glass
panels installed (looking into getting low e) for the two adjacent windows.
The screens did not help since they were on the inside of the window.

Frankly, I'm afraid to continue using the insulated shade with the side
tracks since it causes the glass to get very hot. I'd even bet that the
insulated shade played as much, or even a greater, a role toward causing the
crack than the window film (since the window film was not very effective).

J.

You had a warning from the film co for good reason. Now why not call
glass companys, everyone and you are just guessing here. Go get the
facts from the man that makes glass ....

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

Well, today is another very sunny day. When these insulated shades
(with side tracks) are pulled down for a while, and then I pull them
up and touch the window glass, the glass is hot, and is VERY hot
toward the top 1/3 of the panel (can't even keep my hand on the
panel).
The glass did not get that hot when using the outside mounted levelor
aluminum blinds that were there when I bought the condo.

Do you still think the shades have nothing to do with it even though
they cause the glass to get VERY hot?

J.

Yes.

--
Joseph Meehan

26 + 6 = 1 It's Irish Math

You had a warning from the film co for good reason. Now why not call
glass companys, everyone and you are just guessing here. Go get the
facts from the man that makes glass ....


I just downloaded a .PDF of Anderson's 20 limited warrantee. They list
damage due to "insulated coverings" as an exclusion in the warrantee (as
well as tinted window coverings).

J.

Also, "Four Seasons Sunrooms" mentions that they do not cover damage due to
"use of insulated shades during daylight hours" in their glass warranty.

J.

As I stated in my post we install these inside skylights all the time with
no problem.

Skylights are likely a much heavier duty glass than the relatively-thin
glass on my windows.

Did these shade contain any warning labels about glass breakage when used
with IG units?

No, but they I now believe that they really SHOULD warn about glass breakage
when used in conjunction with the side tracks during daylight hours.

Would they spend this much money on one safety aspect and fail to address
another?

Because they are legally required to address the cord choking issue. Likely
room darkening shades with side tracks aren't popular enough to have caused
too many problems, and likely the odds are much lower that cracks in the
glass while the shades are down would result in death.

By the way, Anderson windows lists damage due to "insulated coverings" as an
exclusion in their 20 year limited glass warranty. Also, "Four Seasons
Sunrooms" mentions that they do not cover damage due to "use of insulated
shades during daylight hours" in their glass warranty.

My point here is that, although I agree with your point that the glass
cracked due to user error (my trying to solve the heat problem from the
inside of the house) , and although I was foolish for putting the window
film on the inside of the dual-pane windows, I suspect the
shades-with-sidetracks equally as much, if not more, than the window film.

Your house, your expense do as you will.

I will likely move the cellular shades into a room that faces the north!

J.

Well if Anderson and 4 seasons have that exclusion then there is an
issue. Good you found out for me I was thinking about your shades. Your
shades are R 5 , that is the highest R for a shade Ive seen, it is equal
to a Tri pane or 1" of pink foamboard is r5.5. True your glass should
not be Too hot to touch. High R shades are usualy meant for night heat
loss. Was there a warning with your shades ? There should have been. I
have Anderson and pella, , maybe the exclusion is new I do not remember
seeing it . Before I get cellulars I will research it more. I just put
in a 5x8 Tripane id hate to break it. Why not just open a window and
get fresh air in.

If the shades are actually any good at reflecting
radiated heat, then you don't WANT low-E film, you want
the light to come in, bounce off the shades, and bounce
back out, without even noticing that there was a window there.

You have a point. However, the shades aren't reflective enough that the
light would simply bounce back out the window. If that were the case, then
the shades would look like a mirror. The light tended to get converted into
heat when it hit the shade, once converted to heat, this caused the heat to
be trapped between the shade and the window, rather than just bouncing out.
Granted the window film wasn't helping matters, but the shades (Which happen
to have side tracks to seal the edges) were causing the trapped heat to
"bake the heck" out of the glass.

J.

Was there a warning with your shades ? There should have been. I
have Anderson and pella, , maybe the exclusion is new I do not remember
seeing it . Before I get cellulars I will research it more. I just put
in a 5x8 Tripane id hate to break it. Why not just open a window and
get fresh air in.

There was no warning. Anyway, the shades would likely not be a problem as
long as the sidetracks aren't installed (but then why bother with a high r
value shade with gaps). With the sidetracks, it creates the seal on the
sides that traps the hot air between the shade and the glass on a sunny day.

J.