Greetings and QUESTIONS from uruguay - rmh from the far far south

hi guys, i hope its ok to introduce myself here and drop a couple of questions.

first i want to thank you all for this site. i ve been reading for a year or so, tho not much time for it.

i m carlos from montevideo, uruguay, uy-italian so could live legally in germany for 7 ys. - in the 90s-  where i finished architecture studies begun in mvd.
still my school was all high tech, and my knowledge about green practices was due to being a neighbour of the green party in berlin, then collecting a book or two every second day.

permaculture is a complete strange subject in uruguay still today. we ve made a social housing project* in 2002, and people and AUTHORITIES  would ask what renewables were.

* all natural materials except for the concrete foundation slab, solar passive design, straw bales walls, all rain and drainage water reuse, recycling of solids, etc etc. we got the "moral" support of the public school of arch  PLUS the ministry of housing, but no money. so its only on paper.

2 ys ago we opened a students residence, and set a cast iron stove replacing the traditional in mvd open woodstove that "heated" the house -aprox 80sq m

in may 16 we found that 20k a day in firewood was too much, considering the ton costed aprox 160 usd, in a land where half or workers earn 400 usd a month.

so we watched 20 or 30 videos, erad a lot from paul , ernie and erica, downloaded free plans for a rmh and built the supposedly FIRST ROCKET STOVE MH IN URUGUAY!
later a canadian friend who lives here told me he d seen another one. whatever, we re second

due to our super restricted economy, we tried to use all possible recyclable materials we could find.
after an outside 1:1 model, we built it inside in 3 days - the basic functioning-  et voila! it worked and WE REDUCED THE WOOD CONSUMPTION IN 75% APROX  going to only 5k a day
i know after so many ys you may not be impressed, but we were!
long story short, WE HAD to use exhaust tubes of 4" as its the standard to spare like 25 dollars per meter (5 usd vs 30 for a custom made 8")

we will try to improve it next week by adding a SECOND exhaust of 4", so going from a 80 sq cm to a 160 sq cm approx whch will be closer to the ca 250? sq cm of the combustion chamber section.

at this point i am tired of writing in english will try to write at least one question!

we are thinking of building next month a second rmh at the rear house, and to avoid the expensive tubes we think of using bricks for the exhaust.

Q1 i think i ve seen some unit bult like that here?

yesterday i saw a video of a workshop in santa fe, argentina, where the guy said exhaust pipes  could be reduced in  section as long as the fumes go colder because of different density , meaning one could begin with an 8" section a couple of meters, go down to 6" some other mts and finish w a 4" for instance.

Q2 do you agree with that? in my particular case it would be great as i would not need to make ANOTHER  hole to the concrete roof slab. i get out w 4"now w the existing stove.

thank you all again.

saludos, carlos

--

winter in uy is 4 months long, no snow, almost never under 0C, BUT too humid at the coast and firewood is almost a must!

i m sure i will have some more questions, but its siesta time, 4pm and 35C outside w maybe 80% humidity! chau y gracias! feliz carnaval!

https://www.facebook.com/asociacion-ecotectura-uruguay-55066021504/

https://www.facebook.com/1924.lodge.mvd/

just after finishing , reading, editing, etc, the post i see at the end "similar threads" and a post of 3 ys ago of a namesake from atlantida, 45 km from here!

nope we are not all carlos in uy! saludos.

The reducing question has been discussed here before; I believe the most knowledgeable answer was from Peter van den Berg, who said you can reduce some, maybe from 8" to 6" gradually, but to reduce to 4" would probably be too much restriction for decent draft. That would, after all, be going to 1/4 of the original cross section.

You can most assuredly use brick or other masonry material for the flue channels, as long as you build tight enough to avoid leaks. Generally, a double wall, like a brick channel surrounded by cob, is safest.

There is another style of mass storage, known as a bell, which may be more appropriate for your materials. It is essentially a big brick box, can be long and low, or tall, with the combustion core feeding to the bottom of the cavity, and the exhaust to the chimney at the bottom, arranged so there is no straight-through flow. The hot gases rise to the top, heat the mass, and fall to the bottom as they cool. Only the coldest gases exit to the chimney. This design has very low friction, so you don't have to worry about duct length.

hi glenn! thanks for your answer. as i mentioned, i plan to try next week to improve our fist stove of last year, where i didnt know about maintaining same section all trhu the system.
so i ll add a 4" second round pipe to the existing one, while the combustion chamber horizontal is around 1 brick rectangular, approx 20cm by 11cm. and a round heat riser of approx 20 cm inside with 1,5" perlite-ashes-cement insulation.

should this work, i ll try our new stove in march/april with a similar combustion chamber now all w firebricks, making heat riser bigger as i see it must work better - we were conditioned last yr cause of existing old stove structure and coudnt make it higher. it s  like only 80 cm high.

then i think its ok to try to go reducing the flue channels horizontally - i have a 2m bench approx- going forth and back and 1 m more (making 5 m horizontal) to then go vertical to the existing 4" pipe thru the roof. should it not work properly, i think i could add another 4" round pipe going out somewhere else, to avoid the hassle of another hole at a 70ys old concrete slab of 15cm plus sand on it, plus brick, etc.

would love to hear your feedback

any pics or links to the bell system? thanks a lot! carlos