Rocket mass heater without the mass

I am considering building a rocket mass heater, but I don't have a permanent place for it yet.
Can I run the horizontal exhaust pipe (about 20 feet of it) without the cob around it? Will I have any problems with exhaust leaks this way? Is the galvanized vent pipe ok for that? How hot would that pipe get?

Thanks.

Without the mass its just called a rocket stove. Plans are available online and the horizontal exhaust would not work because the air will be too hot. The fumes will want to rise up so a horizontal exhaust would backflow into the house.

The reason why RMH sometimes have horizontal exhausts is because the mass absorbs most of the heat from the exhaust fumes which prevents them from rising.

Mike Kelly : Welcome to Permies and a big Welcome to the 'Rocket' and 'Wood heaters' Forum/Treads, With over 19,000 fellow members here at permies you can post here 24/7
and find someone someplace in the world who wants to talk about what you want to talk about ! In this case this is still not big enough for you, please go to our Sister Site
richsoil.com and click on rocket stoves there, this will take you to a series of videos of Rocket Mass Heater R.M.H., builds, by professionals, and supervised by professionals,
There is a specific type of R.M.H. build much favored by Paul Wheaton our Host here at Permies.com and richsoil.com, that lines the stovepipe within a wooden coffer
or long skinny box and backfills the coffer with sand or pea gravel, this is a trade-off that makes A temporary or moveable Rocket practical. These units have to be carefully sealed
and the galvanizing on the barrel heat treated to lock the zinc coating to the surface, this is done with high temperature fire at the same time as you burn off the paint on your 55 gal
drum! This is also covered within these videos! Every thing that you have ever heard that 'is wrong' with the internet, is typicalized by U-Tube, please use a careful eye when it comes
to Rocket Videos found in U-Tube land, there is a lot of stinking shit out there and you must independently verify what you see and hear !

Finally have you been to rocketstoves.com to get your PDF Copy $15.oo of Evans' great book 'Rocket Mass Heaters'? There is STILL No Other book
with as much Rocket Family information in any language (and I don't make a dime !) With ~ 100,000 ~ R.M.H.s built world wide most of them were made from 'The Book' and 95%+
of all the 1st built ones (that worked) were built with "The Book"! Time and effort that this book will save you, and allow you to understand all of the special language of Rocket
builders is hard to spell out here but it is a simple step that will pay you back many times over both in your personal understanding and in communicating with your fellow members!

Think like Fire, Flow like a Gas, Don't be the Marshmallow, as always, your comments and questions are solicited and are welcome ! PYRO - Logically BIG AL !

Cory Arsenault wrote:Without the mass its just called a rocket stove. Plans are available online and the horizontal exhaust would not work because the air will be too hot. The fumes will want to rise up so a horizontal exhaust would backflow into the house.

The reason why RMH sometimes have horizontal exhausts is because the mass absorbs most of the heat from the exhaust fumes which prevents them from rising.

Cory, how many rocket stoves or mass heaters have you made? Are you sure you understand well the principles of physics?


There's not much difference between horizontal without mass and horizontal with mass.

The rate of heat exchange with a mass will be slower than with a bare pipe, thus making theses hotter and then rise more, if they can rise any further in a pipe which stops theses from rising.

Actualy hot gasses don't "rise", they are pushed upwards by heavier gasses which usualy are colder.

Mike, to keep heat, and have a little removeable mass, you could look into bells, relying on stratification to keep the heat on top of a chamber where it gets more time to conduct to the surounding elements. Two barrels stacked on top of each other with red bricks, or pavers, or anything else, stacked around them would take a fair amount of heat to "store" And with a bell, you can go for far shorter horizontal run. Since the mass is vertical, and the heat exchange time is as long or longer than with an horizontal pipe. Where the hot gasses are swept away by the constant flow of gasses.

Thank you for the warm welcome.

Cory Arsenault wrote:Without the mass its just called a rocket stove. Plans are available online and the horizontal exhaust would not work because the air will be too hot. The fumes will want to rise up so a horizontal exhaust would backflow into the house.
The reason why RMH sometimes have horizontal exhausts is because the mass absorbs most of the heat from the exhaust fumes which prevents them from rising.

It seems to me that cob acts as an insulator relative to open air, so the horizontal exhaust will cool quicker in open air.
I would like to have this horizontal exhaust pipe to get some extra heat out of the exhaust. It will also let me test-drive the rocket mass heater before deciding on the permanent installation.
I have seen Paul Wheaton's video on the youtube about covering this exhaust in sand and I will do this if I have to, but I would prefer to just leave the exhaust open for now if I can.

Thanks.

One reason I do not want much thermal mass right now because the floor structure is questionable where I want to put it and might not support the weight very well. I will just let the house be the thermal mass for the time being. But I still want a rocket mass heater design in all other respects.

Mike, bell!

Santamax,


I have played around with a simple rocket stove but have not yet built a RMH though i have studied them during my university studies which involved reading A LOT of materials on them including discussions with Ernie amd Erica. How many have you built? Id be curious to study your build and how youve been able to get a horizontal rocket stove to work since according to my research a horizontal flue withiut a thermal mass would be unable to get the proper air draw through the chamber which would result in smokeback. I notice you advised Mike on how to add a mass, why did you not advise him to build without one?

Am i incorrct that a rocket mass heater without the mass, is simply a rocket stove? This is pretty much what Ianto Evans says in his book.

FYI if we want to debate semantics it isnt necessarily "heavier" gasses which force up the air but "denser" gasses. I was trying to keep it simple.

Santamax, if I understand this correctly, the bell structure will put even more of a point load on the floor compared to a typical rocket mass heater installation where the weight is more distributed over a wider area.

I would like to build it regularly, with the only exception of leaving the horizontal exhaust uncovered.

Other than not having the thermal mass, are there any other problems with this?

Thanks.

Mike,

IMO, if youre planning on just using the house to store heat then a rocket stove with a verticle exhaust might be easier. Are you well insulated?

Building codes tend to disallow horizontal exhausts because of the issue of smokeback I mentioned before. As Satamax said, Id probably put a bell/barrel over it however there are models out there that dont have one.

As you probably know, J-tube stoves have the advantage of using gravity to feed the wood into the chamber which is what I would pick. L-tube models require you to push the wood in once in a while as it burns back.

Mike,

Do you plan on having something to lift the exhaust off the floor to orevent heat damage?

Cory,
Yes, I will hold the horizontal exhaust off the floor by several inches and will probably put cement boards underneath.
The house is not well insulated and I understand the problem with temperature swings in the absence of thermal mass, but it will have to do for now.
I want to use a rocket mass heater design to reclaim more heat compared to a rocket stove, and also to experiment with it before settling on the final design for the permanent installation.
It seems to me that many people must have test fired their units before covering the exhaust with mud. Maybe they can share how it worked.
Thanks.

et al :This is going to give some of you a big horse laugh, or resemble some part of a horse, but Guys , remember the golden rule, and play nice, when you get old
and crabby, that will be soon enough to fence with words, Mostly when I do it, what started in my head is deathless prose before it gets to my fingers,then it turns to shit
at least I have an excuse and a doctors note to prove it ! And yes, call me on my sometimes arrogant turn of speech !

Mike Kelly : Because Radiant heat travels so well through air we percieve that all heat works this way , Convection and Conduction don't, Still air is a great insulator,
it is trapped air, unmoving air, no matter how formed that makes up all our conventional forms of insulation !

You accept that cold water cools you faster than air, and warm water warms you faster than warm air, it is equally true of other materials, when we want to describe
bitter cold we usually pick an object, Cold as a brass monkeys balls, a witches tit, a well diggers ass! The cob is not insulate, it absorbs the heat, and that is the primary
function of it and the other Dense materials placed within it !

I Know of no reason why, after the Thermal differential engine has been created, in the R.M.H.s barrel that the hot exhaust gases will not flow through the horiz-
ontal pipe, and as air is insulative, flow for an even greater distance (everything else being equal,) as through a given length of Cob, would I want this piping under foot
No! could I move it up over head to allow the heat to stratify against the ceiling, Well - maybe If I had lots of ceiling fans !

I am also concerned that much of your heat would still be lost up the vertical chimney, unless you used one of Satamax Antones Bells to extract the excess heat just
before the vertical chimney,I admit to becoming quite fond of bells for that purpose. It does allow for the possibility of radiant heat in two locations ! With the primary
heater always located in the heart of the home - which is what Hearth originally meant !

Warm air is displaced by more dense cold air seeking to find the lowest and coldest spot ! Everything else being equal, warm air does rise ! For the Craft !

Think like fire, Flow like a gas, Don't be the marshmallow ! As always your comments and Questions are solicited, and Welcome ! Pyro - Logically big AL !

So, Mike, a bell can store heat for some time, even if there's barely any mass. Not long, but two or three hours is not out of the question.

About bells.

http://www.stove.ru/index.php?lng=1&rs=16.

If you have a massonry wall in the house, you could heat it with one side of the bell. If made square like old home heating fuel tanks, or agricultural fuel tanks.

Here you can see the double barrel bell on Peter van den Berg horizontal batch rocket.



http://www.youtube.com/watch?v=tpsGO9tY8rY

May be you could make something like this. Two stacked barrels on your rocket. No worries about the barrel gap then. Plus two stacked barrels, like this, aside the rocket, aranged as a bell. Vertical bell, with intake and exhaust at the bottom, and which would store and extract heat from the flue gasses. Then, you could use a little mass around the second set of barrels, to keep warmth a smidge more.

Myself, i'm on the track of using square tanks, and covering theses with bricks, dry stacked. Whenever i can find tanks which i like.

Santamax, what stores the heat inside the bell? Air has virtually no thermal mass. It looks like the material the bell is made of is what captures and stores the heat, so if the bell is light weight, there is not much thermal storage. I can see a bell being useful as a heat-shedding or heat-coupling device though.
My problem is weak floors so I do not want to bring in much heavy masonry. Unfortunately I do not have a masonry wall to connect this to.
Do you have a picture of this fuel tank you have in mind?
Thanks.

Well, check that link. There's plenty of square or rectangular metallic ones. On legs, no legs.

http://www.leboncoin.fr/annonces/offres/provence_alpes_cote_d_azur/occasions/?f=a&th=1&q=cuve+fioul+-plastique+-chaudiere+-cuisiniere&it=1

Well, hot gasses rise in a bell, and are stuck there untill they cool down. Only a certain amount of heat per hour can be transmited through the metal or other material of the bell, so hot gasses are stuck in there for a while. You can store more by adding mass. And the release of the heat is slower too. Meaning longer release time.

This Rocket Stove is apparently the concept I'm going for with mine. It's my first build, and I'm experimenting with using the stove for rapid heat radiation and convection to heat a three-story house. Our basement is exceptionally cold (the rear wall, where the stove exhausts, is a walk-out wall, and the yard is the lowest portion of yard around the entire house), so I want to heat it, but also dry it out more.

My exhaust is 8" diameter, and I'm using HVAC pipe right now. I want the heat to escape from the barrel and the pipe into the room. The pipe is horizontal, with 2 90-degree bends, and it's lying right on the concrete floor; so, that's my "heat sink" for now, aside from a few kiln bricks on top of the barrel.

The only real issue I seem to be having so far--well, aside from leaky cob--is the Stack Effect. Of course my exhaust is in the lowest part of the yard, so the highest pressure zone, but I'm raising the stack to the upper yard level, just above the back eave, which should counter the pressure significantly. I also have a cap on the stack that should assist with pulling draft from the constantly shifting winds up on this hillside.

My outside pipe isn't insulated, either. I'm curious to see whether this will help, hinder, or neither.

There is some air escape in the third floor area, which, I'm attempting to use to my benefit to help pull the "cooler hot air" from the basement upward, while I have a pipe of cold air coming into the basement right to the feed tube.

This is all very exciting...and a little scary.

Mike,

I was thinking about your issue of protecting the floor and I was wondering it it would be possible to coil your corrugated piping into a spiral vertically? This would lessen the floor space taken up and prevent damage to the floor.

Not sure how you could get it to stand up and hold it's shape. Perhaps make chicken wire tubes? An inner which you wrap the piping around, and then an outer to hold it together?

The inside of the spiral would probably get pretty hot and draw air up through it. Not sure how you could use that to your advantage.

Just a thought, I've never seen that done before and don't know what kind of results you'd get.

et al; It suddenly came to me, a little snippet of deathless prose - To share with a select few !

A BELL (depending on location): can hold Some of the Heat most All of the time, and All of the heat for some of the time,but it can't hold all of the heat as long as
A Thermal Mass Bench ! BIG AL!

allen lumley wrote:et al; It suddenly came to me, a little snippet of deathless prose - To share with a select few !

A BELL (depending on location): can hold Some of the Heat most All of the time, and All of the heat for some of the time,but it can't hold all of the heat as long as
A Thermal Mass Bench ! BIG AL!

Allen, it depends.

On the heat release speed of the bell's material. If the bell is slightly insulated it can release the heat slower, therefor holding it longer. And also, depending on the volume. A huge bell can store lots of heat. Tho, it's hard to make it exhaust well through a vertical chimney.

But there's tricks. Downdraft flues Not easy at all!

Allen,

I want to second Satamax's point. The heat conduction and retention properties of the material the bell is made from have everything to do with how long the bell takes to heat up and how long it holds the heat. A thermal mass bench in "the book" is mostly made from everyday or "found" clay. If you were to make a bench from a cast refractory material, instead, which has higher conduction and storage properties, then, the bench would hold the heat longer. Of course, it would also cost a lot more because you would be paying for the material and you would have to figure out how to manage the structural integrity of this large mass of fireclay.

However, if you were to do a side by side test of a bench vs. an equivalent set of bells, the inherent properties of the bell would result in more heat transfer to the thermal mass than the flues incorporated into the bench. The reason for this is the temperature stratification of gases which is facilitated by the bell and not by a flue.

For an explanation of flues vs. bells and a chart of the thermal properties of various materials, see the blog at Dragon Heaters.

I don't know Satamax's definition of a huge bell. But, our 6" test system made with clay chimney flue liners in 2 stacks (1st bell is 7' and 2nd bell is 6' tall) draft really well into a vertical chimney even when it is hot outside. The exit temperature into the stove pipe is about 140°F.

Cindy, huge bell, something like 1000 gallons, or more

It turns out there was a post with an almost identical topic recently: Mass Heaters without the mass?

Erica Wisner wrote:
- Exposed horizontal stovepipe is widely recognized as a firetrap.

So I guess this is not such a good idea. But I wonder why that would be? I guess this horizontal pipe gets hotter than I assumed?

Cindy Mathieu : I believe that the point that you were tying to make was that a properly constructed "BELL" would hold onto the heat energy long enough for it to be more easily
incorporated into a thermal mass!

I have no problem with that statement on its bare surface it must be True. However-

Todays refractory material, is able to create on its surface such high temperatures that easily within the first hour we have already reached the glowing red hot stage where any
piece of wood small enough to fit within the opening of the Feed Tube seems to simultaneously burst into flame !

This is because the refractory material now has such a high rate of emissivity that most of the heat energy is radiated back into the combustion chamber, refractory material is not
To my Knowledge, known for ether its conduction of, nor heat energy Storage !

Some where in your statement is a comparison between the hot exhaust gases within a bell, and the rate of heat energy radiation through Cob, First we would have to deal with the
Temperature drop at the surfaces between Air and any second material. Second, Inherent within this statement is a total disregard of the rate of "heat penetration'' through nearly
every type of stone, this is generally figured as 2Xs the rate of cob alone !

Do I have this wrong, because I thought the reason for substituting refractory materials which are generally softer, and wear out sooner was because they did not rapidly transfer
heat! If my understanding is in error, Then please break it down for me so that I can understand it !

Mike and Jeff : I think that this is just a general continuance of certain safety statements Ernie and Erica both have made, as most of the total length is 'hot enough to catch paper
alight', (famously at 451F) most of its length, it is an accident waiting to happen, I certainly would isolate it from any small kids who can be badly burned at temperatures below 212 F.

Over 30 years ago a grease fire caused my brother-in-law to snatch the frying pan off of the fire, at that exact same moment my niece ran to wrap her arms around dads legs for
protection,- many skin grafts later my niece learned to wear her hair just so, and today is a very beautiful and self assured young lady, But The whole family truly understands the
statement 'It only takes a second ''! Hope that this is clear and helps start a dialog ! For the Good of the Craft !

Think like Fire, Flow like a Gas, Don't be the Marshmallow ! As always, your comments and questions, are solicited and are Welcome ! PYRO - Logically BIG AL !

I've just finished building a 14' x 14' room on the back of my house. The room is designed to be my solar
heat storage area (that will rise into the house) and be a place to build a RMH. I've noticed that some builders
use tape to seal the joints between pipe. Can anyone tell me what type tape to look for/use?

This will be my first RMH. I'm going to need plenty of hand holding to get through this. After reading some of
these post, I'm a little worried about leaving an uncovered pipe run. I do all my building myself and it'll take
a while to cover all the pipe with cob.

I like the idea of a bell at the end of the pipe run (just before it leaves the room to go outside). Can you build this out of cob?
Can it be a small enclosed cob space? Say a 4" thick cob wall, 6" open space (for the bell)? see photo

Pack Mckibben : There is a kind of Ductwork sealing tape that will work for you- mostly-It has a shiny aluminum surface, is a little thicker than most grades of 'duct/duck'
tape, there is a layer of paper over the sticky side of this tape that you just peal off ! You will have some longevity problems between the transitional area at the bottom
of your drum and the first 6 feet of your Horizontal run of stove pipe due to high temperatures, as long as you paint on a layer or two of clay slip to help bond the Cob to the
Pipe, And do the first 6 feet first, it should not be a problem !

Because I have not seen a discussion about burning the paint off of the barrel and any gunk inside, as well as heat treating the first several feet of galvanized stove pipe in
this Thread, I am going to ask you to go to - ' richsoil.com ' - and click on Rocket Mass Heaters, there is a series of videos of R.M.H. builds done by Ernie and Erica Wisner
or under their direction that you should watch in their entirety, but definitely watch the Barrel burning segment !

Outside of that, I like every thing you have shown with your sketch, except the last Two Elbows you added to hook in your Two bells, I am sure you did it that way for ease
of making the sketch, these are not needed, and will retard the flow of your hot exhaust gas stream, parts of your bells will act like elbows, and you don't want to stall that gas
flow, It takes a very long chimney to correct a problem you do not want to build in !

For the Craft Big AL

Allen: thanks for your reply. You're right about the drawing. I don't know sketchup that well. I draw the duct square when it'll be round
just because it's easier to draw square in sketchup. I'm not sure I'm going to build a bell at the end. That drawing was to get folks
thinking about what I should, or shouldn't do/build...

I've been watching videos for years on YT. Paul Wheaton, and Ernie and Erica. I've already watched the RichSoil videos you refer to.
I've already burned off the paint on my drum (years ago) and plan on doing it again, per videos, soon. So you're saying I should also
put the first few feet of stove pipe in the burn too? I haven't seen that in any video...My plan is to use black stove pipe from the
drum to the first TEE, then use the silver galvanized pipe (like they use in HVAC ducting) the rest of the way out of the building.

Is the tape you're referring to the tape that's in HVAC area's of the hardware store? Foil Tape? Can you give me a brand name for the tape?
I'd like to use tape, but because of the high temp, I'd like to make sure I use the proper tape...
Look forward to talking to you guys later....thanks

There's a woman who lives near by that has been using a RMH for three years now. She's going to be my supervisor in this build. I'll be asking
question to the group though. She didn't use a drum; she used bricks to build the heat riser surround; and then used a barrels steel top, mortared
in for cooking/heating tea...

Pack Mckibben : This is the weekend and my favorite places are closed, I checked out lowes and all they had was crap tape and cloth backed crap tape, again if you want to
make the effort, you want the slightly, stretchy, shiny, silver/aluminum tape that the sticky side is faced with a paper ribbon that you pull off, as always, measure twice cut
once, or make/have a pattern ! Please take lots of pictures and back them up with phone pictures, NOW would be a great time to practice with both, please be nice to your
instructor, ask her to be allowed to share pictures of her build especially how much of it she tiled / Cobed,

I would not be afraid of any used stove pipe that was not shiny, But what did you use for a chimney to draw flames out of your barrel if you didn't use galvanized pipe, Black
pipe? Anyway there is nothing wrong with the way you are doing it, help the others to get a good, hot, clean burn, and leave it to the mycelium's to break down the remainder
after you bury it in fertile - non crop ground, a flower bed will do !

Sometimes the only way to deal with dumb questions is to say " try it and let me know how it works for you'' ! IF YOU hear your instructor say this more than once. you all need
a break ! To learn the most about Cob and Rocket stoves you need a happy instructor, good luck !

With several builds under my belt, I have yet to construct any type of a Bell, and I feel like a small fraud every time I say that a bell might work for you ! You may have a work-
ing bell before me ! My next R.M.H. I will build, will be an outdoor one in North Carolina ! For the Good of the Craft ! Big AL !