Will A Temperature Change Caused by Fire Line Crack Mirror?

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rody084
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Hello,

We have an installation in which we will be placing a 1/4" thick mirror which spans 7ft across and 5ft in height directly next to a "line of fire" (a gas pipe with holes which will have a flame approximately 6" in height).

Our concern is that when the line of fire is turned on in the winter (when the mirror is cold) the sudden temperature change will crack the mirror. We were thinking of placing the line of fire 12" from the mirror but I was wondering if anyone knows a way that we can calculate this to determine whether the mirror is in danger of cracking from sudden temperature changes.

Thank you!

Rody
 

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Not easy to calculate, you would need to know how quickly the air heated and what the air flow was between the flame and the mirror is.
I would have guessed that if the flame is above the mirror and is only transferring radiant heat there isn't much of a problem, if the flame can go up and reach the mirror it is more likely to be a problem.

Leaving aside the flame, you might need to worry about how the mirror is fixed. If such a large mirror is fixed to a metal frame and is exposed to large temperature variations (day/night?) you might have a problem stressing the mirror without the flames. You might need to be careful to mount it with some compliance.
 
I don't know what country you are in but in the UK something like that would have to be installed by a formally qualified and registered gas engineer (CORGI), and properly ventilated so the viewers don't get ill from carbon monoxide poisoning or set themselves on fire. The gas professionals might have some data about the heating issues - and talking to them early about something "non-standard" like this would seem like a good plan in any case.

You could consider using a metal mirror rather than glass - no cracking problems with that, and it would probably be lighter as well. I'm thinking about the plated steel sheet for making tin cans etc which is supplied and transported in big rolls, so getting a 7x5 piece shouldn't be any problem at all.