Mid December 2016 our miniature 12,5cm / 4.9inch CSA (cross sectional area) Rocket Mass Heater got finally finished and we could switch off the stinking gas heater, that was bridging us through November, waiting for our RMH construction to begin. It must be said, that this is our first experience with heating with wood, as we come from a life with central (gas) heating including a digital appliance on the wall to input the desired temperature. Yet, ever since the RMH is completed, our dragon is the only heat source in the house, except a radiator for the bathroom. It gets fired roughly twice a day (morning / night) and keeps us warm even through the exceptional days around freezing temperature, that we had in our usually mild mediterranean, warm temperate climate.
Our RMH is a very small model with a CSA at the lowest end of the scale and also a battery (mass bench) at the lower end with only about 0,5m3 of volume. The sizes derive from an existing chimney flue of our rented house (CSA limitation), and the size of the corner of the living room that could be furnished with the heavy thermal bench.
Here you see the built in the first air tight drafting test, loaded with bricks as well as under construction images of the bench, being filled with field stones and thermal cob and the adjustment of the sloping of the bench channels.
Having read The Rocket Mass Heater Builder’s Guide by Erica & Ernie Wisner after getting aware of the RMHs through my initial Permaculture researches, the development and building of our RMH became something like my gateway to Permaculture. It was the first real Permaculture project I became engaged in and it proofed to be extremely simple, magorly genius and purely satisfactory in its outcome. So, empowerded by this experience I felt confident to engage in more permaculture projects and put a lot of trust into Permaculture design techniques, that bring easy to apply, ancient knowlege into nowadays problems solution finding.
Photo after the RMH’s first burn at final state: The white upper part of the heat riser indicates a very hot burn. This is a sign, that high temperatures are achieved and a thorougly combustion of the fuel is supposable. The black lower part shows the soot, that condenses on the cold surfaces of the RMH’s innards at the beginning of the burn.
Fuel math and facts as conclusion:
Having counted the buckets of fuel that we burned in our RHM from December till now, I can well estimate that for a whole, future heating season (November trough March) we will need about 3,5 m³ of fuel. In american cords this will be about one cord of wood. Of course this number resembles a highly subjective value, as every person has a different sensation of heat, every RMH has different potentials (remember ours is a mini RMH, with a mini battery and therefore short piping, loosing substantially more heat through the exit cimney pipe than other RMHs), and every house is different in size and themal properties, so are the climatic factors in different locations. Yet, now being surroundet by many people, heating with wood we had many smiling people sitting on our heater, confirming the unbelievable little amount of wood the heater uses and definitely wanting to construct one themselves.
- From December 13th to today, March 5th, all ashes from all burned wood fill one of the 13 liter metal buckets seen in the top image.
- Wood, that would keep us warm for 10 hours would fire a conventional wood stove of a friend for 2 hours.