http://richsoil.com/heat In some of my earliest videos I show building a heat riser with metal on the inside. This is a disaster for any rocket mass heater that gets good an hot. Steel is liquid at 2600 degrees F. Never use steel in the burn tunnel or heat riser. There is some debate about using steel in the wood feed. Steel, or any metal, outside the riser has been fine. A perlite and clay riser can be formed with a wood or carboard form which will be burned out later. Or a steel form that will be slid out. At the 2015 rocket mass heater innovators event, Peter van den Berg built two rocket mass heaters that fit into a barrel. We talk about metal in the core while looking inside the one he calls "Minnie Mouse". He points out that there is just a short amount of steel in the wood feed - and it is okay because it is air cooled to keep it from getting too hot. Also, a 4 inch system cannot hold as much wood as an 8 inch system so it will naturally burn cooler. Our conversation then turns to explore the vermiculite riser which is held together by stainless steel screws. There are different recipes for stainless steel and each recipe has a different melting point: about 2400 degrees to 2800 degrees. So about the same as mild steel. Then we go back to talking about high temperatures with steel. The first problem is that steel spalls at about 1300 degrees F. Steel spalling is when the steel turns a light gray color and flakes off. An alternative form of oxydizaton. It has to do with the high temperatures and levels of oxygen and carbon.

More about rocket mass heaters in our DVD set at

https://richsoil.com/wood-heat.jsp


Thanks to Dan Ohmann of The Grass-fed Homestead channel for helping me with the editing:

   / @thegrassfedhomestead  

Relevant stuff at permies:

https://permies.com/t/52544/metal-bur...
https://permies.com/wiki/63837/Wood-H...
https://permies.com/f/260/rocket-mass...
https://permies.com/wiki/63312/Rocket...


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