greg crawford

Yes Erik, we were thinking to source the fresh air intake from the basement at first... only, at this point in the house-rehab, the basement is suuuuuuuuper drafty, which would just let in all that cold winter air -- which is the case with the house in general. To sidestep the problem, we thought to pipe it in from the chimney. At this point however, it is just a wondersome thought.

Our 8" RMH is (functionally) finished. The combustion unit's dimensions were reduced proportionally, so that the surface of the barrel is at a more cooking-friendly height. Nearly all materials (excluding the ceramic refractory insulation, perlite, HVAC piping, foil tape, & gasket) were found/salvaged around our nieghborhood in Detroit. Not to mention, these found materials were shuttled by bicycle trailer. It still needs all the finish, detail work... next summer.


3 cleanouts (one at the manifold, one at the 3rd turn in the mass, and one at the base of the chimney for cold-starting as well as debris management. We decided to install a damper at the base of this 35 ft chimney (which was lined with HVAC, to better 'close' the system, so that the chimney's ferocious draw doesn't export all of our precious heat. This was a very, very good idea.

This heater sports an integrated plant bed, to overwinter tender perennials, and, we hope sub-tropicals (now doing research for low-light requiring, winter-able plants

This heater also includes a 'hay box' -- a super insulated container for passively cooking food w/out fire. No, the thermal mass does not feed the insulated box -- just a cosmetic connection.


The heater performs well. The mass reaches 100 degrees f, while 17 outdoors. We haven't been able to burn such fantastic wood yet... just crap and lath. The lath is great, just FAST burning. We haven't needed to cold-start the chimney; not a single smoke-back start. Love that rockety sound! Our issue is our 1903, 3,700 sq ft, un-insulated, super-drafty house... which we are beginning to bite into. Also, our heater draws sooooo much air; you can feel the cold seeping through... so, I am planning on dropping a 6" pipe down the other chimney, to act as fresh air intake. Very curious to see how much this offsets the dragon's hunger for air...

Thanks for everybody who contributes to this forum -- it's proved to be an invaluable resource. Here's to a warm winter!

just want to clarify: you believe that the proportional reduction in dimensions should work?

yes, i will do a dry-stack outside, you've talked me into it! in fact, the whole project may as well even be faster, with what i learn in the dry test

thanks again al!

allen lumley wrote:Greg C. : a Typo sliped into your building plans Thread regarding your proposed length of your Thermal mass !

The thought had popped into my head you were having problems convincing your other half to let you drag all
that mud into your house !glad it was a typo! For the craft ! Big AL

aha, yes, so i have decided to drag all that mud into my house! i will be building a double-bed-sized mass-platform, & abandoning the plunger-tube which would utilize the chimney's mass.

and so, what do you think about my question now

Mister Ianto says in the 2nd edition that: "The height [of the heat riser] in the specimen 8-inch system shown is 33 inches, but could be anywhere from 25 to 50 inches."

with a heat riser height of 41.5" i should be clear (according to Ianto). then, if all dimensions are kept proportionally intact... couldn't i expect (logically-hope for) success?

thanks for the reply al, but your advise is a bit confusing:

allen lumley wrote: The p[roblem with Curtailing the greater part of your Thermal mass is you are only capturing the prompt heat that comes off of the Barrel approximately 40% of the total and only a very small pert of the remaining 60% you total will be near 50% total with 1/2 the heat being vented to the outdoors !

Al, by 'curtailing the greater part of my thermal mass' are you saying that my run of 44 linear feet is not enough for an 8" system, or, are you saying that reducing the dimensions of the combustion unit (proposed reduction is 6/7th or 86% the standard size) will cause a failure in system heat capacity/efficiency?
*if the former, you think a run of 44 linear feet (a loss of 6' in a standard 50' system) can be considered 'the greater part'? i suppose i can add another 6' feet to the mass run; if so, duly noted, but my question pertains to the combustion unit.
*if the latter, what does the combustion unit dimensions have to do with curtailing the thermal mass? that the heat generation/output would be decreased by a proportional reduction in combustion unit dimensions?

allen lumley wrote: Whole height must also be figured as distance from the top of the bricks covering the burn tunnel

this distance is simply the height of the heat riser, minus the 7" depth of the burn tunnel. again, nothing relating to cross-sectional area has been changed.


again, thanks for the response. i am hoping that once this is sorted out... i will be on my way to winter heat!

the standard height of the metal drum surrounding the heat riser tends to be quite high on an 8" RMH system. following the design dimensions laid out by E & E (as well as Ianto), puts the top of the drum at about shoulder height. which is not an ideal cooking height.... at least not for a 5'8" kind of dude...

if proportions for heat riser (3x), burn tunnel (1.5x), and feed tube (x) are still followed & as well all cross-sectional areas are kept unchanged... can i still expect good performance if the dimensions are dropped PROPORTIONALLY?
i am hoping to have a heat riser height of 41.5", a burn tunnel length of 20.75", & a feed tube length of 13.8. this would put the top of the barrel at elbow-height, rather than shoulder.

a couple additional pieces of info:
we are only running 44" linear run through the mass (so a little less pump-effect could be tolerated)
we are exhausting into a 35" existing chimney (which acts as a second pump)

Zach Weiss wrote: The purple permaculture that Sepp saw in Detroit was more along the lines of hand holding and dancing around howling, pretending to be wolves. These kinds of activities Sepp does not feel comfortable participating in, and does not want his to be associated with.

but, in many ways, we are so many wolves holding hands, dancing and howling, in Detroit... i would not expect someone like Sepp to feel comfortable in such a rabid place as this city... it is most certainly not an idyllic, fresh-aired, natural wonderland (well, it sorta is, actually, in its own way...).

and yet, i have no knowledge of Sepp's actual visit in Detroit, as i wasnt around at the time. thank you for prompting me to question permaculture yet again -- if only permaculture can continue to question itself, relentlessly, through observation...

i will be checking in with my local hardware store first, but my backup is amazon, since delivery is free (and i am car-less )


FIRE BRICKS -- my (repurposed) fire bricks appear to be glazed... it is a shiny, thin glaze which wraps around the entire 4-sided exterior of the brick. is this a (health, heat, etc.) concern?

HIGH HEAT FOIL TAPE -- amazon carries Multi-Purpose HVAC Foil Tape, does this seem appropriate?

MASS DUCTING -- i believe i remember reading in 'the book' that the first stick of piping (the first 5ft-ish, connected to the manifold) ought to be of stronger durability than the rest of the ducting through the mass. any recommended gauge-size for that first section? after that, it seems that the ducting quality is negligible? would generic Round Metal Duct Pipe suffice?

GASKET -- @ $30, this Door Gasket Kit is pretty spendy. any DIY/thriftier options available?

MANIFOLD -- do folks prefer cob-molding the manifold, or buying a prefab?

PIZZA STONE -- learned of the pizza stone from Konstantin's post and wanted to share a way to make it for $3.

while listening (enjoying) the 2nd 'innovators event' podcast, i heard all agree to Paul's statement that a vertical chimney is about 2.5 times more effective than the heat riser, in terms of pump-power.
reading through this post (https://permies.com/t/27052/rocket-stoves/external-chimney-RMH), i can also refer you to Peter's quote of: "Make the chimney taller. Double hight of the heat riser (and barrel) gives approx. double pumping power."
also from the same post, also from the same Peter: "As long as the temperature inside the heat riser is much higher than in the space between the insulation and the inner surface of the barrel, the pump should work. So the exhaust gases can be cooled down to any temperature without affecting the function of the RMH."

i will be piping my 8" RMH into an existing, 35ft chimney. if the above is true, and an 8" system gives me 50' run of horizontal ducting (incl. 5ft per elbow) through the mass... do i then have at least (a theoretical) 100' of additional run to play with? or is this outrageously simplified?
provided my exhaust is above the condensation-point of 122 degrees f, and the chimney flue is warmer than the outdoor ambient temp, can i add another 'run'? though, what i have in mind is not more horizontal ducting.

what i do have in mind is if i can seal-off the fireplace and make 2nd bell in there? or, preferably, a plunger-tube within the sealed fireplace?
i would like to keep that hot air (above 130f) in-house as long as possible, in contact with mass for as long as possible.