Arthur Cooley

Here are a few images of the space and tentative materials to be used...feedback, critique, encouragement, etc. more than welcome!





As you see, I have acquired some 150mm (6in) ID terra cotta drainage pipe, with a T and Elbows, that I hope to use as my flue over which we will put our cob. As you see, the run will be pretty small, about a meter out and back and then I will use standard stove flue to take the exhaust up the interior wall about 1200mm and then through another terracotta elbow through the wall. The cardboard mold you see will be used to create the cavity used for the feed tube (plus ash catch below), burn tunnel, and then the base of the heat riser. My heat riser will be a clay slip mixed with perlite packed in the space between 150mm and 240mm flues. The main chamber's composition will be clay slip mixed with ash and pumice and then surrounded on all sides by cob. And the cardboard mold is 150mmx125mm (6x5inches) for each cross section. Yep. That's the direction we're heading for now.

Regarding the 30' that's so often referenced, what is the impact on the functionality of the heater if this length is cut by half or a third or even two-thirds? Is it simply that heat is being lost out of the chimney? Or will it diminish the efficiency of the combustion as well? And if one were to cut the length of of their horizontal mass-heating run, what impact will this have on the exit temperatures?

I am keen to try to have the flue exit as low as possible and have read suggestions that it is still highly advisable to have a high-reaching chimney to promote draw, but it had occurred to me that with a shorter horizontal run, perhaps the lower chimney could be more plausible?

And thank you Allen for double checking those dimensions for me! Your replies have been enormously valuable and greatly appreciated! Cheers.

allen lumley wrote:Right now you are getting some of the coldest temps ,in a basically Maritime Climate ? Right ? and it will be 3-4 months until things warm up !

That's about right. And the temps really aren't getting below freezing at the coldest time of night/dawn.

allen lumley wrote:1st thought Casually introduce the idea in ALL conversations with neighbors and friend of Neighbors that you are Adding a simple forge into your Work space in your
garden shed, And will probably have to move it outside when it warms up !

Ha. Nice suggestion. I will most certainly consider that route.

allen lumley wrote:I see about 3 rocket mass heater builds in your future ! The simplest build and easiest to live with is a J-Bend, Vertical feed, (150mm ) 6'' Rocket Mass Heater RMH. This is the Space heater that you learn on !

The more we read, the more inclined we are towards this direction. As for the proportions Evans mentions in his book (and that are frequently mentioned elsewhere), I would like some clarification of the beginning and ending points for different lengths. The vertical feed, the burn chamber, and the heat riser. Does the length of the heat riser begin at the corner of that "J" or does it begin at an imaginary plane where the burn tunnel extends to the end of that corner? and does the burn tunnel measurement account for the entire horizontal length? or do we subtract one or both of the vertical sections (feed and/or heat riser) when calculating this measurement. (Hopefully this makes sense)

allen lumley wrote: After you have mastered the 6'' system it will be possible to talk about attempting to build a 4'' system - Newer adaptations
of this RMH Include a horizontal fed batch loaded 4'' that when built correctly can perform as well as the 6'' - However experience is the only way that can give you the
hands on experience that you need to move up to a 4'' system - many people who try to build a 4'' RMH (100mm) as a 1st build Fail and then we have to deal with the
" I tried that - '' ''It doesn't work'' '' Its a bunch of Tripe " fail out !

Whilst looking for the basic information on RMH I must admit that I have been most intrigued and impressed by all the developments and innovations folks have developed.

allen lumley wrote: Now the Thermal mass Thing- I hope that I can encourage you to take another look at its practicality ! All we want to do is raise your bed up off of the floor and place a
heated Mattress Pad or possibly a futon pad ! when you want just the bed warn you keep the covers on when you want the whole space warmed say during bathing you
remove the covers and let the room warm ! Actually Elevating your bed will reduce the need for supplementary heat - Did I mention that your Thermal Mass can be
used to store Coolth for you ?

While I appreciate the thought, in theory, the practicality of providing this sort of mass is a bit daunting right now. As mentioned, our space is only 3.5 meters by 2.5 meters, with our straw mattress on a pallet framed bed taking up almost exactly half of the room. That leaves an open rectangle of 2.5m x 1.7m. I was thinking that perhaps I could even just build the unit in the corner and then have a meter run towards the bed, then back, and then up about 1.5 meters and then out the wall. We have access to clay drainage tiles that have an internal diameter of 150mm (6in) and I was hoping these might work. They are in 450mm lengths and I was hoping it might be feasible to mold form my own elbows to connect the straight runs. I know a lot of heat is meant to be lost with each 90 degree turn, but obviously I'm suggesting dramatically reducing the runs and the mass anyway.

Also, just to make sure I understand what you're suggesting Allen, are you recommending a large mass to put the mattress on top of? So, for us it would effectively amount to 2.5m by 1.7m by however high, perhaps 500 or 600mm? And then running my exhaust through this? I was uncertain what to imagine when you suggesting removing covers to heat the space vs. just heating the bed.

allen lumley wrote: If you have not already done so Borax can be sprinkled into your bedding to reduce a fire hazard and Baking Soda makes a good fire extinguisher for wood and oil/
grease fires !

Good to know!

allen lumley wrote:
Fire bricks - O.K. Thats an issue, Our fallback position is 100 year-old dead-soft Red or orange red house bricks, This kind if rubbed on a sidewall (or concrete ) will
leave a mark behind in the same way that Chalk leaves its mark behind on a Sidewalk ! This is an adequate Feed Tube and Burn Tunnel for a Vertically fed J-Bend Style
6''RMH

How about another fallback? No thoughts or input regarding a cob mix? I was inspired by some comments made on the donkey32 boards as well as what I read about this chook brooder built out of cob. Hopefully someone emerges with some solid, useful information about taking this route.

allen lumley wrote:
Perlite : Have you checked local green houses for horticultural penlight? Vermiculite , or pumice , or expanded Clay pellets can be made to work ! ( I'm counting on
otherMembers to chime in here )

The perlite that comes in box stores (equivalent to Lowes or Home Depot) is only 5L (about .2 cubic feet) and is about $10. At 100L (about 3.5 cubic feet), it's in the $40-50 range, but one must order it at pay about half that again for shipping...alas, the price one pays for living in a nation of merely 4.5 million.

I do have 20L, so about .8 cubic feet of perlite I ordered (for nearly $40!) and was hoping to use this for the heat riser and come up with another recipe for the burn chamber.

Again, I do have collected pumice and sawdust, so perhaps these might be used?

I'll be sure to check your maths as well!

Thanks so much for the detailed reply to my query. I will keep you apprised of any progress.

Cheers.

I will begin with the context of our anticipated build...we live in a fairly experimental, some might say rough, situation...it works for us...but here it is...

-My partner and I live in a technically illegal <10m2 (100ft2) wattle and cob (ish) structure we built beside our garden we've developed on a friend's property.
-The structure is comprised of four chunky green eucalypt rounds buried a meter in the ground with poplar/willow poles running horizontally (rather than vertically) at about 20-30cm spacing between the poles originally intended to support the cob, which is only about 10-20cm thick (depending on spot, highly irregularly applied, with curves in walls, etc.)
-The footprint was dug out about a spade's depth, backfilled with broken clay drainage tiles, covered with race lime, and then we put just a 100mm cob baselayer floor (next spring/summer we'll do it up a bit better, but winter was approaching and time was running out)
-We live in temperate New Zealand - we get the occasional frost but it really doesn't get below freezing very often.
-We have a roughly queen sized mattress/bed that is simply a duvet cover stuffed with straw (ie, highly combustible) and this takes up half the room.
-The ceiling/roof is simply corrugated iron sheets laid over round, hardwood pole perlins
-No electricity, absolutely no desire for anything with gas, so in search of a wood heating option

Hm, what else might be applicable...?

-Oh, yes, we don't mind the cold in the least and have no interest in a heater for our own comfort...but we'll be introducing a baby into our lovely (unheated) environment in the next couple of months and feel compelled to do what we can to bump the internal temperature up a few degrees on those odd frosty nights...

Yes, so, we obviously don't have much space. I don't even know that a mass would be workable for us. Certainly not 10m of mass-encased flue. And we don't really anticipate using this heater any more than a couple dozen times...tops (but who knows). Hopefully next winter our new addition will be all good to "rough it" with her parents (we enjoy our layers of woolen blankets).

Some concerns:

-Proximity of barrel and/or burn chamber to corner pole (which could be cobbed over or ___ to protect it) and/or walls with embedded poles
-Possibility of running flue out wall and, if so, feasibility with embedded poles
-Potential for a less mass or even mass-less heating system.
-Oh yes, it'd be great if the flue was not rising out of our "garden shed" (ie, home) like a red flag for noisy neighbors, passersby to easily conclude that it isn't actually an out-building.

We would prefer to build something that is mostly cob. I haven't been able to come across any firebricks. I ordered some perlite (only 20L as it has been difficult to come across and is quite expensive, but more could be had if need be). Um, I have two 100mm diameter, 1200mm lengths of flue pipe, one of 240mm diameter, 1000mm long, and some 150mm diameter flue pipes.

I have a 60L drum I hope to work with, measuring 380mm across by about 570mm high. According to all the research I've done over the past weeks, it seems it'd be tight, but perhaps with a raised cob core it could be workable (if I go with a J-tube design, but wouldn't mind an L-tube if you educated folks suppose it'd be better).

Yes, I will gladly post some photos of the structure and site if it might assist any of you (to assist us!).


Please, please lend us your wise suggestions. We feel like we're pretty handy folks and strive to take care of ourselves as much as possible. We entering new territory here though - with heaters...and babies - and we just want to get some advices from folks with experience.


Thanks in advance.


Cheers! Art.

Emily Aaston wrote:
We also decided to build the core entirely out of cob (heavy on perlite for the burn tunnel and heat riser). Unfortunately, we were in such a hurry that the manifold and heat riser collapses on us the night before the chicks were to arrive. But we decided to buy two more pieces of stove-pipe that was filled with perlite-cob to replace our heat riser and after a week or so of burning the heater, it was dry and ready for our chicks!

Is the cob mix you used include heavy use of sand and straw, or is it modified for the rmh application? And I have read about potentially using sawdust that might burn out in lieu of perlite - what do you reckon? It's just that perlite down here is awfully expensive. We can get hold of pumice at the beach though, do you think this might suffice?

We're personally aiming to build something similar but for an indoor (100 square foot) space, with a 15 gallon barrel, to be used very very sparingly, and without expectations of it lasting more than one winter season.

I'd be keen to get started, but want to ensure our cob mix is at least suitable.

Any advices from any of you kind folks would be greatly appreciated.

Cheers.