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Cracked fire brick at burn chamber bridge

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bike rocket stoves woodworking
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Hey Guys.
My RMH has been up and running for a season and like most J-Tube setups the first brick over the burn chamber has cracked.  The question I have is, do I care?  I've seen several other J-Tubes, one of which is 20 years old, that have cracked bricks here.  

It seems that once that brick breaks once it's probably not gonna break any more.  But I have nothing to back that up aside from intuition.

Perhaps I could replace this brick with something of higher quality?  Maybe a ceramic kiln brick?

How are others dealing, or not dealing with this problem?

[Thumbnail for cracked.jpg]
First fire brick over burn tube is cracked. What to do?
Posts: 329
Location: Penticton, Canada
building woodworking rocket stoves
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Hi Rich,  A very common occurrence indeed! Here are a few scenarios: 1) Some people don't worry about it as it now acts as an expansion/contraction gap and doesn't get any worse over the years. 2) Some people are concerned that it might cause the brick to fall out, block the air flow and cause the house to fill with smoke so they replace it. With the same type of brick or other but ultimately it does have a tough life.  3) While others have decided to do something about it right from the get go by taking preventative action and putting a metal plate in front of it called a Peter Channel. There has been tonnes of discussion on it so I won't repeat what has been said other than one of its functions is to help block the heat from this first brick and keep it from cracking.

I think this might be the first discussion on the birth of the Peter Channel. A bit lengthy to read but gives you a good background of its birth and implementation:
Peter channel

Peter Channel
yeah, but ... what would PIE do? Especially concerning this tiny ad:
List of Rocket Mass Heater Builders
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