A few nights ago I had a good fire going with the
tempered glass doors closed on my pre-fabricated
fireplace. Well, I guess it got too hot, after an
hour or two, because one of the glass pieces shattered
into small cubes. No biggie, I had a replacement, but now I have
1. The fireplace has tempered glass (it is a "Majestic BR42")
whose glass doors are able to withstand a documented gradual
rise to 550F.
Did my fire get that hot? I admit I loaded it with 4 or
5 small logs but it was not roaring by any means (I had
good embers at the bottom tho that were burning quite hot).
2. I'd like to not worry about the glass doors anymore.
My choices are a) get rid of them, b) never close them,
c) rebuild a *real* fireplace or woodstove, or d) get
better doors. I'd like to do d) for now. If I were to
replace the glass, should I simply get thicker tempered
glass? Or is there some other product that is the same
thickness (3/16" or 1/4" I don't know for sure) that has
extra heat protection?
3) Assuming a correct installation (the home builder installed
it so you never know, but assume for the moment). Using
standard wood for fuel, could I cause the fire to get so
hot that it catches something on fire inside the wall, like
some studs or drywall or insulation? Is it really that easy
for a residential fireplace to get so hot with traditional
fuel that it is a hazard to surrounding material used that
is "to code" in all respects?
Thanks for any insight!
Not sure if you're fire got too hot or not but I would think the glass would
trap a lot of the heat with little escaping to the outside. If you have a
choice, you might consider replacing them with a screen.....it'll allow more
heat to pass as well. I can get my fire going pretty hot (never measured
it but I would think it's above 550 degrees easily). On the install, it's
hard to say what you've got. Fireplace clearances and dimensions are
pretty specific but for the pre-built units, I'm not sure what they are. I
do know that for a built fireplace, you need 8-8.5" behind the firebox of
nothing but masonry or air (I see different opinions on whether it's 8 or
8.5" and whether or not to leave an air space), the mantle should be 12" in.
minimum above the opening, and wood members shouldn't come within I think 2"
of the fireplace masonry but you really should check that. I'm building a
fireplace now outdoors and have no combustibles near it at all so I really
haven't paid much attention to the clearances required. If you do decide
to build your own, I believe a footing of 12" thick that extends 6" beyond
the footprint of the fireplace is necessary. It may not make sense for you
if you're in a slab floored house as you may have to cut out an opening in
your floor to pour a footing that thick.
Screened opening makes sense if you're trying to heat the county, at
the expense of cooling your house, or if you want ventilation in spring
or fall; else you gotta be nuts. A fire at 550F is a smoker; over 1000F
Forget the screen. Go for a properly-designed woodstove or insert and
hook it in, and get some useful heat out of it without having to wear a
flack-jacket and full-visor.
I wouldn't worry about it.
Tempered glass can blow up for absolutely NO reason at all. You will
probably never have this problem again if you simply do nothing.
This may sound like a half-ass answer but it's the truth. I've been
holding a piece of tempered glass in my hand and had it blow up for NO
Ever heard of a doorglass blowing up in a car before for no reason?
Call any glass shop and they will tell you this.
BTW, I'm sure there is a scientific reason for it but a glassman isn't
a scientist : )
Had that happen to me once, scary as anything. Just buckling my son in
his carseat in the back after church one Sunday, my wife is standing
next to the car talking to some people, and BOOM, the entire back
window shatters into a million tiny pieces. We puzzled over this for
hours. No cars were going by (to throw a stone), not under any trees
(something to drop), very few people around on sunday morning (to throw
or shoot something), no one was touching the window at the time or for
at least an hour prior, not a very cold or hot day (for temp stress),
not windy at all (?). It was a pretty old window -- probably 22 years
The glass repair company wasn't surprised at all. "Happens all the
time" they said, explaining that it is just a terrible coincidence of
stresses and wear and whatever, combined with old glass, possibly a
tiny defect from the manufacturing, a hairline crack spreading slowly
over time, or whatever. But the effect is that it seems fine one minute
(we even scrapered ice off it that morning), and next thing you know it
is just bits and pieces.
I'm sure there is a reason, you just don't know what it is. [g]
I had the pane of a sliding glass door spontaneously self-destruct
"for no reason." We were sitting right there when it started. My
wife first though the PITA neighbor kid shot it with a bb gun but it
was the inside pane of a double-pane glass. It actually took a minute
or so for the crazing to propagate over the whole surface.
The windshield on my car broke a while back. For a few days there was a
small "y" shaped crack, then it went all the way up. I suspect it
happened because heat was uneven. Car has been sitting in Florida sun
for 8 years. Even morning sun is surprisingly hot, and I think the
sunny side got hot before the shady side did. Slider could have had
just a scratch, and enough stress from heat to expand it. After all,
glass cutting is just extending a scratch.
Had the glass on a gas grill explode once, but that was because it was
hot and it began to rain.
Why snip my post when I wrote the following?
"BTW, I'm sure there is a scientific reason for it but a glassman isn't
a scientist : )"
Tempered glass explodes all the time. If there is a reason, I've never
heard of what it is in the 26 yrs that I've been in the glass business.
The best answer the OP has received to date.
This happened to my fireplace years ago, replaced the glass with a new piece
and it has been good for over ten years now.
Any defect in the glass will be exposed under the extremes presented in a
fireplace installation. Tempered glass is only designed not to shatter into
dangerous, sharp shards. Many people think it is the same as bulletproof
The only thing you want to be sure of is that the glass is loose in the
frame. You need to account for thermal expansion. If the glass is tight to
the frame when it is cold it will be stressed when it gets hot. And you have
to clean the crud out of the frames regularly too.
This doesn't answer your question, but about three years ago I bought a
glass and screen doored one for out firplace from Home Cheepo. While
installing it I was suprised to see the instruction sheet warned against
closing the glass doors while a fire was burning inside.
I thought this was strange, since the box it had just come out of had a
nice color picture on it showing a fire merrily burning behind the
closed glass doors.
I went to the manufacturer's web site and found similar photos, so I
hooked an email to them asking why the instructions said not to do that.
I got a wishy washy answer from them saying that it was ok to close the
doors on a fire "most of the time", but that an extra hot fire could
possibly cause the glass to shatter.
WTF? We've gone ahead and closed the doors on plenty of fires in that
fireplace since then and the glass is still OK.
Probably not the heat but uneven heating. Glass doesn't conduct, and if
the middle is hotter than the perimeter of the glass, it would logically
be stressed. Any tiny scratch is the beginning of a crack, just like
when you use a glass cutter.
I'd contact the company and complain. If it made for heat, it should
not explode. Besides someome could get hurt and they would have a
legal case. Even if they dont do anything they at least know, but
likely they will give you a free door. Who knows, there may even be a
recall. All it takes is a phone call, email or letter.
The old wood stoves used mica, that never broke.
I should note that you could have had the wood too close to the doors,
The fire should be to the rear.
I agree with the guy that said you are losing heat with glass in
front, a screen is better. No sense wasting the heat with fuel prices
what they are.
Of course there is one other possibility.....
Did you notice a guy wearing a turbin near your house?
Could be terrorists <lol>
On 5-Feb-2006, snipped-for-privacy@UNLISTED.com wrote:
How does the glass reduce the heat?
Replace the glass with a screen and the air flow will increase the rate of
combustion and carry the heat up the flue. Using glass doors, properly
sealed, increases the efficiency of a fireplace by a lot. They reduce the
air flow and allow you to choke down the fire. That's why glass doors
have been used on fireplaces for the last few decades.
Since glass doors are quite common and they are there to increase
efficiency,, it is not reasonable to assume that they shouldn't be used.
I think the most reasonable explanations are either that the glass had a
scratch or crack in it and differential heating caused the crack to propagate
or that some liquid (was the wood really dry?) hit the glass and caused a
significant temperature gradient locally.
It has always amazed me how few people know that glass doors are supposed to be
closed when you are burning a fire. I always try to appeal to the pure logic of
it. If they are not supposed to be closed while the fire is burning then what
is their purpose? The fireplace already has a flu to close when you are not
burning a fire so logically there is no purpose served by glass doors at all
unless they are closed while the fire is burning.
I mean do these people think they are there to keep the cat out?
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