Sandy Mathieu wrote:The kaowool with the rigidizer might hold up, only time will tell. The cinder blocks however may not really the best option. Based on the size of the barrel he is using and the channel the question, the issue is, what is the temperature entering the cinder block area? It should be less than 400F, Since his barrel is small, it is likely his heat is higher than the 400F. Long term this will result in the cinder blocks failing. The other issue is that cinder block is not very good at thermal mass. See the chart posted at this blog. If you are going to make the compromise on temperature it would be better to use solid cement blocks.
But more firebricks would serve the best.
http://blog.dragonheaters.com/category/reference/thermal-mass/
Well, kind of he same numbers here, but not exactly, concrete does a better job at transmitting heat than firebrick. But doesn't accumulate as well, even with heavy loads of stones in it. One advantage, it's cheap.
http://www.engineeringtoolbox.com/thermal-conductivity-d_429.html
http://www.engineeringtoolbox.com/specific-heat-solids-d_154.html
Concrete can cope easily with 100C°
http://en.wikipedia.org/wiki/Concrete_degradation#Thermal_damage And can whistand up to 300C° without too much damage. Worth a try for it's cheapness (tho, it's cheaper in europe, due to more widespread use)
If in europe, you can find pozzolan chimney flue elements (concrete with pozzolan) which are rated for 400C°. In the case i've showed, i don't know about longevity, but it's thermal conductivity is not as low as on your chart, because the conductivity is not dampened by the air gaps. His flue gases going directly through the place where the air gap usualy is. Well, worth a try on my side of the
pond. May be not on yours.