Jessica Gorton wrote:I thought of that too, but I have seen tubs made from similar materials that could be sealed against water. Some kind of cement, perhaps? And that's another question: does the Mass in the RMH have to be cob? It makes sense that it is non-flammable, easily formed, etc, but are there other materials that could be used? Stones, mortared together or mixed with cob? Anything else?
An alternative to the cob tub would be a regular tub sunk into the cob - use the cob as thermal mass without needing to waterproof it.
We moved to an area with really silty soils, no good for cob, so our current heater is fieldstone (rocks stuck together with a natural mortar). Two of our neighbors used brick for their heaters - one did a box of brick and then tamped some mineral soil in for the thermal fill, the other built it pretty much solid with bricks and mortar, and just used mortar and chipped brick to fit around the round pipes.
One of the nice things about getting interested now (as opposed to ten years ago) is there are a lot more good, working examples you can copy without needing to study the physics of _why_ it works. I would still recommend geeking out a little bit on fire itself. You can do this just by spending quality time with it, and trying little challenges like making a rocket cooker or chafing dish heater or whatever interests you. Learning to run a clean fire, and confidently adjust it if it's not burning to your liking, is a wonderful life skill / lifelong practice.
If the tub was made well so it could be drained completely - like with one of the waterproof plasters, or even a cast-iron tub encased in cob for moderately comfortable heat transfer - no reason it wouldn't work. Straight cast iron tends to get way too hot for comfort.
Let's see: other rockety ideas I've liked but haven't had time to do yet:
- Maple syrup boiler (we don't have sugar maples so I have to practice by proxy)
- How small a miniature J-tube could we make that would work? Is there a naturally small fuel (like pine needles or something) that would self-feed in such a tiny stove?
- Small incinerator: with good testing gear, can we design a system that can burn petrochemical garbage safely? Hospital incinerators used to make tons of dioxins, and we don't want to do that. But rocket mass heaters have been made over to burn coal and wood pellets and other fuels. Can we get the system calibrated for plastic garbage?
- Batch water heater (SAFELY) - we've done some work with other qualified water heater guys to do tank heaters that heat up slowly for safety, but I have an idea for a batch-heater or on-demand heater I want to play with.
- Water as thermal mass (SAFELY) - lots of ways to do this either rocket or otherwise
- Cookstove for clean fire yet moderate heats, such as low-temp frying (rocket stoves tend to be kinda full-bore: "high" and "freaky high" were the settings as one cook described them) -we used bricks to diffuse the heat, but is there a method that would allow even more control over more burners? I think we might try this one at Paul's place next year.
- Rocket bake oven that produces a good quality of baking (a lot of them are kinda uneven heat, especially if metal floors are involved). I want it as good as a traditional brick oven or earthen oven, even better than modern kitchen ovens.
- I want to learn to do more kinds of masonry heaters like tile stoves or pot-ovens, but need a good source of robust ceramic materials of a certain shape.
- Rocket powered electrical generator (I saw a camp stove / griddle version that had a heat-powered generator that would charge cell phones; I want to play with it and find out if there are bigger ones and how reliable they are)
Yours,
Erica W
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