a question on layout of stovepipe in the cob mass heat storage unit

i am in the process of building a rocket stove mass heater more or less based on Ianto Evan's book, and have constructed the firebrick feed tube, burn tunnel and riser with a vermiculite/perlite insulation tube around the heat riser. now i need to construct a roughly square footprint 4' x 7' cob heat storage all in my 10' by 12' cellar (which has other limitations on floor space).

what i would like to do is instead of using the serpentine layout as shown in Ianto's book, i want to use a system where the rocket stove gases enter an 8" dia. manifold pipe that has about 5 reducing T's in it which connect to five, 6" dia. stovepipes running 5' long, parallel with each other in the cob, to rejoin into another 8" exit manifold pipe at the other end of the mass. at the ends sharing a common wall facing the rocket stove, the manifold pipes would each have a cleanout access thimble/plug that would allow inspection/cleanout of all the ends of the 6" dia. connections to the manifold pipes. i think this is a better heat exchange arrangement but my wife insists that i get some feedback before commencing construction. so, any thoughts or has this already been discussed in detail? all replies are welcome. thanks!

Robin Redmond : Yes similar designs have been discussed here. Anyway you still get credit for thinking outside the Box

No Joy here ! What would you think of starting a company with 4 other people- all equal partners ?

With just one division into 2 pipes -irregardless of how carefully you matched the sizes and the elbows/twists, and turns,
one would become dominate over the other Every Time ! Also " Ts " and Especially Reducing " Ts " will kill your Budget !

It might be possible to add a series of blowers into each pipe section being controlled from individual air speed sensors,
but Even then I would not guarantee the pipes would be carrying equal Amounts of heat Energy !

Reducing the size of the pipe carries its own problems and mathematics, when you reduce the size of the piping by 1/2
you reduce the Cubic inches by a Quarter this and this smaller piping comes with an increased amount of Reduced flow
due to (proportionally) a greater percent of friction loss at the pipes walls !

Ask any fireman - Paid or Volunteer, In order to calculate Water flow to a fire they have to grasp the basics and will
quickly tell you Cut the size of the Fire hose by 1/2 cut the Flow by 1/4

Have you been to Rocketstoves.com to Download your copy of the new 3rd Edition of Rocket Mass Heaters by Ianto Evans ?

I also strongly suggest you try you new Rocket out of doors before bringing it into the house, an important part of testing
your Rockets Characteristics is to place the barrel over the Heat riser , Sealing the Rocket Base well at that manifold, and
immediately installing your final Vertical chimney.

After you have proved that your Rocket Burner Core will Draft well with a Final Vertical Chimney you can finish your
Horizontal ductwork and Thermal Mass this just helps you pinpoint your problems if your rocket has drafting problems later !

There are several potential problems with installing any Rocket Mass Heater in a Remote location, especially when in a
basement. Please Take the Time to Google " Stack Effect " and " Whole House Stack Effect "

Often -especially with a basement location you can have bad problems with smoke back during startup and Also quite
commonly when trying to use your Rocket and Run Any Exhaust fan any where else in your house !

Common problems with exhaust fans include running a Clothes drier, or your Stoves Range hood exhaust fan, or even
the Exhaust fan in your Bathroom !

With These few issues in mine, read the book and then come back here soon. We all use the same words to describe the
sizes, shapes and orientation of parts individually and to the whole !

If there is a Rocket in your future we will help you find it ! For the Good of the Crafts Big AL

Thank you Allen for the quick and meaty reply. Lots of good objections to the idea.
Enough for me to back away from it. The advantage to it, besides being able to clean out both manifold pipes, was in a better use of the floor space, but I will persevere in using the original design. Meanwhile, the rocket stove part is already mortared in place but I will test it before building the mass heat storage.
The room is newly closed in and is unconnected to the rest of the inhabited portion of the house, and the only access is through the wood shed. This was to eliminate smoke in the house. We hope to heat water in an open reservoir sitting on top of the heated mass from a coil around the barrel, with heat exchange pipes in the reservoir to carry the heat to the rest of the house. Eventually we want to incorporate solar water heaters to the same water reservoir, using coils in the reservoir to keep the solar panel working fluid separate from the reservoir water.

Robin Redmond : 1st my warning about U-Tube. A good U-Tube Source should look like a Poker Full House 3 videos all about the build and running the Heater

with recent updates, does the poster have a good relationship with viewers with questions, And maybe a pair or more of Videos on a different topic that he

is keeping current ! So 3 or more of a kind and couple more showing handyman skills - A full house or better.


The Kiss of death is One " Look what I just did'' video with no follow up or recent posts and a poor rapport with viewers ! Joker card videos
-dangerous to Trust


So here is a video to show you one good way to have a vented Water filled container that won't create a swamp affect in your basement
-rotting sills and floor joists

See link below :


https//youtu.be/oiwnYqcRLZw?t=16m10s:

The video should start where the vent fill tube is being constructed - This can be plumbed so that you can tell from upstairs that you have
sufficient water in your system ! and a drier basement !

Good luck ! Big AL

You can have a 7' square mass easily and with much less expense than running lots of parallel ducts through it, or one serpentine duct with too many bends. Look up Matt Walker's "half-barrel bell" concept. Essentially, you run the RMH barrel exhaust into the base of a 55 gallon barrel sliced in half lengthwise, and connect the exit from the bottom of the other end of the barrel. You can have two or more half-barrels in series, going from the bottom of the last one to the chimney. Because of the large cross section relative to the duct the hot air slows down, rises to the top of each barrel, stratifies, and gives up its heat before cooling, sinking and exiting. It also has very low friction.

The other factor Allen alluded to is more problematic. Even if you have perfect mechanical design and don't experience smokeback or other issues, putting a typical RMH in a basement accessible only through a woodshed is very likely to become a chore to run and be neglected. It will require tending every 10 to 20 minutes or so for the duration of the burn, and if you are not next to it constantly you won't know when it needs tending, so you are likely to have it go out on you frequently or else have to sit next to it waiting for it to be ready to feed again. You should only have a J-tube style RMH in a room that you will be using continually while it is running. What are your plans for this basement room?

There is another type of RMH combustion unit called a batch box which would be suitable for operation in a remote location, but it would mean dismantling much of what you have already built. If you want to learn more, you can research it, or we would be happy to tell you the basics.

hi Glenn, thanks for the reply. i should have checked in here a day earlier. i just purchased most of the 90 degree bends and associated other miscellany for a serpentine run through my heat mass. the half barrel bells sounds very doable, but too late now...
as to the cellar room accessible only through the wood shed, this is because we are trying to eliminate any woodsmoke in the house. we both are in our sixties and have both lived with wood stoves for 45 or so years, and we realize we really need to be done with smoke in the house, even small amounts.
i am used to tending the current stove in the part of the cellar that is connected to the rest of the house, so running up and down stairs is not a big deal for me.
we are hoping to also utilize the water tank sitting on top of the heated mass as a heat sink for waste heat from an engine running a generator (our backup for our solar PV system) as well as 4 solar water heater panels (designed and built circa 1980s) i have yet to set up, and finally also heat from a charcoal production unit i want to set up outside the wall of the RMH room under the outside deck. so really, the RMH is only part of the entire setup, but of course will be the most consistently relied upon portion to heat the water tank.

new questions:

1) is there some reason that concrete could not be used instead of cob to bury the stovepipes in?

2) how less effective would be just pouring in dry sand/clay soil to bury the stovepipe than cob?

hi Allen,

your link:



https//youtu.be/oiwnYqcRLZw?t=16m10s:

The video should start where the vent fill tube is being constructed - This can be plumbed so that you can tell from upstairs that you have
sufficient water in your system ! and a drier basement !

didn't work for me. but i am interested in seeing whatever it was you were referring to.

Robin R. : A slightly longer version link below :






Again what you want to see starts at 16min 10sec

Sorry about he bad link this should work !

Looking for a specific link to problems with high humidity problems in basements ( Molds, musts, and smuts, and Dry rot !)

when I find it I will add a new Thread Extension ! Big AL

Robin R. : Here is a quick video from the Great people at Cold Climate Housing Research Center Univ. Alaska,Fairbanks. You and I know Cold, they KNOW COLD !


https://www.youtube.com/watch?v=xtJhyY8aRLU&list=PLBtw7qpC24vIjGhkRaSyvR1u4G1RRtwxL&index=6

The interesting point starts at 3:30 - The system of insulation described then was actually code just a few years ago and there probably are millions of homes with

Fiberglass Insulation right up against the foundation Sills, While some people have a strong dislike for foam insulation I have a stronger dislike for rotting foundations

For the good of the Crafts ! Big AL

I've embedded the video for you Al.

Robin; i hadn't seen this before.

For the arangement you want, you should look into bells. Or even dead end bells. If you want to build your bench with earth, may be matthewwalker's half barrel system would be good for you.

Thanks for all the replies! It will take a bit for me to wade thru the videos and clues though. Today I have to remove paint from my barrel, and maybe also decide to level the concrete floor before beginning the mass heater. i've inadvertantly got a drop of 1/2" to 1' over 8 ' and i'm planning on using 4"x8"x16" regular half blocks for the perimenter wall instead of mixing straw with cob, and i want as level a surface as possible for bedding them onto. i would still like to hear from anyone that has used dry sand/clay instead of cob. i saw the video of the experiemental portable RMH Earnie had built and how he used pea stone and rocks instead of cobb, and seems to me that packing just dry sand/clay would work at least as well. i'm a little leary of building this too permanently, in case i want to change something basic internally.

i am trying to re-consider the possibility of using the half-bell method, but before i give up on the flue design, i was wondering if anyone could tell me the maximum number of 90° bends i can put in without stalling the velocity of the draft? i currently have 10 including the vent shifting to a vertical exit. approximately 32' of run with 10' of that outside under the deck.

Robin, just with bends alone you would stall the stove! And i'm noy talking about the 32' of straight pipe, plus ten of un insulated under the deck.

Do you have any vertical chimney?


Have you seen this?

http://s65.photobucket.com/user/mremine/library/NYC%20Rocket%20Stove%20Build/#/user/mremine/library/NYC%20Rocket%20Stove%20Build/?page=1&_suid=144316184475009607432420433886

Well, it's still a pipe thought, but à bit like a bell. As it's just over the 4XCSA mark for an eight incher. I think Matthew went too far in this case with his half barrels. Too many of thoses.


In your case, the reccomended "internal surface area" for the bell, is about 5 or 6m², if it's an eight incher. So 6 half barrels aproximately.

Thanks Max. I only have space for 4 half bells, which would still entail at least 5, 90 degree bends. Is there a known limit to 90 degree bends for an 8" diameter system? My available space for all this (within the insulated perimeter wall) is 57" by 91" and the inlet pipe will be coming from near one corner and the outlet pipe needs to be centered on the opposite end of the mass from the rocket stove.
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Well that didn't come out as planned! Oh well...

Robin Redmond wrote:Well that didn't come out as planned! Oh well...

Do a hand sketch, that gonna be easier for ll of us. then you scan or take a pic of it. And host it here.


You haven't answered my question, do you have a chimney?

Sorry Max,
No I don't for this. I intended to run this out to a T just under the eaves and then run it vertically maybe 4' to 10' stopping a few feet from the roof overhang and sheltered by it.

That last post didn't manage to attach the photo which had the caption "exit end of the rocket stove currently"
Maybe this will work (just now learning how to use this iPad...)

The drawing you did with the "plunger tube" at the end could work.

Providing you have a chimney behind.

You don't need the bend in the plunger tube. The advantage of a bell, is the stratification of the gases. So you just need the pipe to go to the middle bottom of the two half barrels, and leave a "ring projection" from the 8 inch "chimney" of about 60 ish square inches, between the plunger tube and the floor. That's about 2.5 inches from the floor. May be 3 inches would be better for security.

Realy, get your tube going up against the wall, as you planed, insulated, and use two elbows to escape the roof eave, and go above the roof peak. Realy, the horizontal chimney described in the Evans book can only work in a place where the prevailing wind is always the same, absolutely always. Otherwise, the wind presure against the wall induces an overpresure in the "chimney" and you get bad smokeback. Been there and done that

But what you've drawn looks like it could realy work. You have less ISA than needes, so the elbows won't matter as much as in a pipe only layout.

For the chimney connection, if you put a 10" x 8" reducer, you can locate that right at the floor and get plenty of flow. You could also use a piece of 10" duct between the sides of the half-barrel sets and have better flow with less friction. Or you could use a piece of 8" duct opened into a half-circle (half of a 16" diameter) and get full flow between the sets of barrels.

hi and thanks for the suggestions Max and Glenn.

i am a little puzzled by the descriptions, ie: "ring projection 3" off the ground"
And I wonder what you mean Glenn about the 10x8 reducer

The reducer is a fitting that goes from 10" diameter to 8" diameter. The 10" end connected to the barrel would allow easier transition in airflow (the same thing the ring projection is meant to ensure).

As well your transition or plenum here seems a bit small.

https://permies.com/t/50024/a/32516/thumb-image.jpg

I would think enlarging it is a good idea.

I agree with Max. The best way to enlarge it would be to round off the inside corners where the sunken ring channel meets the exit channel, taking probably about 2" or so off of the corner. This assumes that the existing exit channel is 8" x 8".

Satamax Antone wrote:http://donkey32.proboards.com/thread/1406/calculating-ring-circumference-projection-gap

Ok I figured out, using the minimum 1.5 suggested at the post you linked to, my 8" diameter system would need a 3" gap at the top of the barrel. I had only planned for 2 " so I will have to adjust the height of the barrel for that.

As for my "sunken" collection ring, it is nominally a 1-1/2" gap, 2/3s of the way around the barrel, at the top, which is what you can see in the picture, but the cavity widens to 3-1/2" at the bottom, which is 6" below the top of the collection ring. And then the two sides of the collection channel dump into the central chamber which is 6-1/2" wide and 7-1/2" tall, before transitioning to an 8" diameter stovepipe and the first clean out.
This sketch is a side view of the situation (cast in concrete...)

Also the channels widen a bit at the top from 1-1/2" to 2-1/2" as the approach the central chamber.

With the opening 6 1/2w x 7 1/2h, you definitely have a flow constriction there. Even though it is nominally the same cross section as the 8" round duct, the sharp edges cause an effective reduction in area and you will have added drag there. You really want to expand the opening (by the way, this opening is commonly called the "manifold" in RMH terminology). It should be no less than 8" wide, and the corners where the manifold meets the inner channel need to be rounded off smoothly.

You mention "concrete"... what kind of concrete is this? Regular portland cement concrete will be destroyed quickly in the interior flame contact areas, so I hope it is not that.

It is. I was under the impression that the hot gases were cooling down by the time it had reached the bottom of the barrel on the exterior of the heat riser. The rest of the rocket stove is fire brick with refractory mortar on a floor of firebrick held off the concrete floor by regular bricks with vermiculite insulation between them. This concrete was poured to be the platform for the barrel to sit on, so the only concrete that is touched by the gases is within that canyon of a collection ring before being exited out the central exit chamber. Also, I am planning on cooling the barrel with copper water coils around the outside of the barrel to heat an (open) water tank sitting on top of the heat mass. So, what do you think? Should I try to destroy the concrete platform?

Well, it all depends on how hot your gases are at the bottom of the barrel. Less than 200 celcius, you should be ok, tho, your concrete, depending on the mix might spall, which is no good. Then only way to tell, is to try.

Since the concrete is already there, and not in the hottest part of the area, you may as well leave it and monitor for spalling or other damage. Heat it very slowly and carefully the first time to allow water to evaporate without turning to steam - that is what causes the spalling. You really do want to ease the corners, though, as that can limit your airflow and permanently decrease the system's effectiveness.

I woud advise keeping the exterior accessible in case of need, not building anything too fancy or permanent around it until you have a sense of how it is working.

Thanks for the advice, and I agree and will try to champher the corners where the collection ring joins the exit chamber. Also, the slow short burns to acclimate the system and keeping it somewhat accessible for future changes is smart. I was just given a gallon of paste-like refractory mortar and may try to "paint" the exposed surfaces of the concrete in the collection ring with it. Thanks for all the thoughtful ideas!