Hi everyone. I'm living in uruguay. And I'm getting ready to build a rocket mass heater. The plan is to use a 55 gallon drum as a cook top, and use the mass part to help warm a greenhouse at night.
Since I'm in uruguay, the kinds of materials that are cheaper or even available is a little different from the US. But I should be able to find enough of the right things to build it.
I have a source for a 55 gallon drum. For the heat riser, I'm thinking a stack of fire bricks would be ideal. Do I need to mortar these together or can I just stack them? The reason I ask is because getting the right mortar will be a fun spanish lesson. So I'd prefer to go without it if it's possible. It would make moving it later easier if I need to.
I know the magic distance between the top of the heat riser and the 55 gallon drum is 1.5" to 2". Is there a similar magic distance between the outside of the heat riser and the 55 gallon drum? It seems like the heat riser, burn tunnel, and inlet need to be 6" wide on the inside.
For the mass bench thingy, I can get galvanized sheet metal pipe. I plan to stack (relatively poor quality) concrete cinder blocks into a bench, put the sheet metal pipe inside, fill with sand, and top with 2'x2' concrete pavers.
Does all this sound ok? There are 100 different rocket stove designs out there. So I'm trying to get a feel for which variables are the really important ones.
And lastly, what kind of temperature can I expect at the surface of the 55 gallon drum?
The heat riser can indeed be constructed of high temperature brick, either dense fire brick with added exterior insulation wrap, or insulated fire brick (IFB) which requires no additional insulation. Whichever brick is used it is important that the air spaces (leaks) between the "stacked" brick be sealed. For that most folks use a simple mortar made from masonry sand and clay, or even clay "slip". Constructed with such mortar, the heat riser (and all combustion unit brick work for that matter) can still be disassembled later if desired, and most of the mortar reclaimed if desired.
Sand for bench fill should have clay added, which is necessary to fill all the tiny insulating air spaces between the grains of sand for a more suitable thermal mass. This too, can be later crushed, removed, re-hydrated, and used again when the stove is moved to its new location etc.
There are lots of multiple bits of info. like this and much much more contained in the builder's guide book. Highly recommended reading.
Hi Brian; I don't know how cold it gets in Uruguay but an 8" system may work better for you in a greenhouse than a 6". Also as byron said sand alone is not a very good mass heat holder , use some clay mixed in.