Marco Ernst wrote:Hey Amos, have you fired up the rmh yet? I am also busy with a heating project and my system is very similar than yours. My only headache is the thermal mass. What to use! My rmh is on top of the ground so I am building a box around the exhaust that I need to fill with mass. I do not have access to clay so cob is out. I was thinking 13mm stone aggregate. Give some feedback on how the soil works as mass.
Cheers
Marco
I have fired it up. It burns great! I was lucky ( or unlucky for my back's sake) that the ground I am digging through is neary all clay. Being so close to the river there is a lot of sand already in the clay. I will post some more pics or videos to see the final results. I back filled the duct in the ground with a paver sand. It is sometimes sold as manufactured sand. It has the consistency of crushed pea gravel mixed with sand. It packs well is doing a good job of holding the heat. That was then covered with clay that was left over. The final floor will be covered with a weed barrier then pea gravel.
It is worth noting that until the greenhouse is covered with plastic it is hard to tell how well the "mass" is holding heat. One thing is for sure by the time the exhaust reaches the exit point it has lost all of its heat to the ground and only emits some steam. After the ground fully dries out I will have some better data to refer to.