On Wed, 29 Dec 2010 23:00:23 -0500, "Ed Pawlowski"
wrote:


If the crack opens and there is wood behind it, there is fire potential. If
it is brick or concrete and the crack does not open, nothing will happen.
You may want to have it evaluated though. I don't know if it can be
repaired with furnace cement or not.

I didn't know anything about furnace cement but I see some brands say
they're good to 2000 F.

http://en.wikipedia.org/wiki/Fire says

Temperatures of flames by appearance
A Fire at 1/4000th of a second

The temperature of flames with carbon particles emitting light can be
assessed by their color:[10]

* Red
o Just visible: 525 °C (977 °F)
o Dull: 700 °C (1,292 °F)
o Cherry, dull: 800 °C (1,470 °F)
o Cherry, full: 900 °C (1,650 °F)
o Cherry, clear: 1,000 °C (1,830 °F)
* Orange
o Deep: 1,100 °C (2,010 °F)
o Clear: 1,200 °C (2,190 °F)
* White
o Whitish: 1,300 °C (2,370 °F)
o Bright: 1,400 °C (2,550 °F)
o Dazzling: 1,500 °C (2,730 °F)

I don't think my flame was ever white. Even the oil furnace flame is
only yellow, which is not listed here!

Parker Furnace Cement says it's good to 3000 F.

That doesn't mean it will stick, or even that I shouldn't do something
else. But the cheaper brands of furnace cement were only 5 dollars,
not 385!