Brian James wrote:Disappointing news - my traveling companion had to back out due to health reasons, and it's not a trip I can or should attempt by myself due to my own health troubles, so unfortunately I'm not going to be able to attend the rocket heater Jamboree in Montana after all.
Glenn Herbert wrote:Concrete blocks should work fine for the mass. I might keep them isolated from flue/duct contact for the first few feet of duct run (with cob or refractory cement), but after that the gas temperature will not be high enough to damage the block.
You do want good contact between the blocks and the flue gases encased in ducting; even if you don't have access to much clay, using cob to fill between duct and blocks is a good choice. Air gaps will kill the thermal conduction into your mass.
Peter van den Berg wrote:John, the heater isn't more powerful just by restricting the gap. The top of the barrel's getting hotter, that's all. Logical, because the riser is closer to it now, good for cooking on top.