Rocket Mass Heaters
Please keep us posted, sounds like you are on the brink of success!
@annesley Thanks for the reality check about using aircrete for the riser. The rocket mass heaters I used required me to stoke every 10, 15, or 30 minutes depending on the firewood available. I would do this for an hour or two during which an incredible amount of heat was stored into the mass and then released gradually into the cozy living space over the course of the next 24 to 48 hours.
The heat riser in this heater uses an aircrete refractory mix developed by this guy. He used to work in a lab testing concrete. The recipe is available for download on his Etsy if you are interested in checking it out. https://www.etsy.com/listing/597937472/air-crete-refractory-mix?ref=shop_home_active_5&crt=1
I have a lot more to learn about Rocket Mass Heaters but what thru me off this guy,,,
Honey Do Carpenter youtube that you are referring too,
is that he throws a lot of heat out the stack pipe rather than keeping it in the home
stored in "Mass".
I might not be understanding him correctly, but I have tried to study what he is doing.
He fixed a stove, tore it apart and his fix was to insulate the stack pipe so that the pipe stayed
hot and drew out the heat better.
I will stay tuned, appreciate the conversation.
The best built rocket mass heaters I've seen have super hot fires in insulated boxes to burn the fuel as cleanly and effectively as possible (hotter fire = more mass is converted to heat energy = less smoke emissions). Fireboxes that are wrapped with thermal mass actually cool down the fire - not the best place/time to extract the heat. The insulated riser powers the intake and exhaust flow so that the super-heated gas has plenty opportunity to then run through a thermal mass storage bank before exiting the building cool and clean. The best system I ever used would burn so clean yet extract so much heat that when the exhaust finally came out of the house (knee high off the ground) I could put my face directly into the exhaust and breathe it in*. The air exited the building at about 95ºF after running through some 40' of lateral cob benches.
That's what i'm talkin bout! Bring it on home brotha!
In my opinion, the goals with a rocket mass heater are to:
- Extract as much heat energy as possible from the fuel
- Release the cleanest exhaust possible
- Store as much of that heat in the home as possible
These goals can be realistically achieved in the upper 90th percentiles using known techniques as established by CobCottage and others. Releasing clean exhaust is a BIG deal when living in a tight village setting.
Sums it up nicely!
This is my understanding as well.
That is why I was confused with the YouTube guy,, Honey Do Carpenter,
when he insulated his exhaust stack just before exiting the home so that it would draw better.
From what I have seen,, designs loop the exhaust then bring it back up to
rise by the original riser so that it gives it a bit of a heat boost to draw on out further.
According the rocket mass heater theory as I understand it, the best place and time to get power for your system is the riser itself. The force of movement generated in the riser will draw in the fresh oxygenated air and push out the exhaust. After the exhaust gas has cooled, it is considered counterproductive to direct it upward against gravity. The power of the riser is significantly increased by every inch of its height and by each additional 100ºF. The more power a riser produces, the longer it's horizontal exhaust can be, the more heat can be extracted into the mass.
I love this forum everyone is sharing knowledge and asking questions. I am going to invite HDC to come address some of these questions about his particular design. Yall bring up relevant points that deserve consideration. I know he spent months of experimenting with the aircrete refractory mix alone. Yall are a wonderful group!
I owe some overdue thanks to Mr Gibran and the Domegaia team for taking the time to share their knowledge of aircrete on youtube. It is a subject that quite frankly I have become obsessed with. Darwin Arnold over at the Honeydo Carpenter Channel expressed his admiration of the Domegaia Team as well. In this video Darwin addressed some of the questions we have been discussing on this thread. I would ask that you consider donating to his Kickstarter if you find it a worthy cause.
This video gives you summary of where he started and the refinements.