stratification chamber for a rocket mass heater

Shamelessly stolen from the world of masonry stoves, the word "bell" with rocket mass heaters can mean several things.  So we go with "stratification chamber" to reference heating the mass (as opposed to the similar stratification that happens in the barrel).  Matt Walker is building the outdoor rocket mass heater with smoker as he describes the stratification chamber technique he prefers.  He likes to use a half barrel.  

He mentions filling a tub with water and if you flip it upside down, you fill it with hot exhaust gasses.   It comes with interpretive dance!  I felt like it might not be clear to everybody, so I paused, added an animation and description, and then rewound and did the thing with matt again - my thinking is that on the second pass it makes a lot more sense to everybody.

My animation shows filling a bucket with water because the water is heavier than surrounding air.  Then I flip it upside down and fill the bucket with hot air.   This is the same sort of effect you get with a hot air baloon.  I then demonstrate that the bucket conducts heat, so the gasses in the bucket cools as the surrounding air is warmed.  

In time, the heat stratifies with the hottest air at the top and the coolest air is at the bottom.

A regular rocket mass heater has a duct that starts low and finishes high.   The heat is forced to the far end of the bench.  The vertical exhaust near the barrel gets a bit of extra heat to make it rise - a tertiary thermosiphon.

All the crappy animation is by me!  

On a larger scale this would be called a kang bed stove or a roman hypocaust.  

After raising the manifold exhaust, use a hollow bench - with a large cavity.   The hot exhaust enters the chamber and spreads out evenly.   Then the coolest gasses are extracted from the bottom.


More about rocket mass heaters in our DVD set at

https://richsoil.com/wood-heat.jsp

Awesome!

Matt has a slightly longer video discussing similar material - Rocket Mass Heater Bells and Benches Discussion

Yup, I've built benches that way too. Old Permies post And found it worked quite well. I'm waiting for the next big thing... getting the smoke to go down hill. (which has also been done before) Where instead of a chimney, The flue is directed through the earth (such as the under the "umbrella" of a high mass annualized solar home) till it is chilled enough it flows out at ground level downhill of the dwelling. The weight of the chilled flue gases can pull the warmer flue gases in the right direction. Siting would be important as a hollow below could collect the CO2 and be hazardous. (don't go "rollin' in the clover)

Anyway, I have not had the time or the room to go much farther with this. I had hoped we would be moving to a larger chunk of land before now so I could build a high mass house heated with a high mass heater to try this out more thoroughly. Possibly in another year.

This is the same principle behind the operation of any RMH which incorporates a bell (stratification chamber) instead of having a serpentine flue running through a horizontal mass. This is the same physics as I used in designing and building my 7” steel cored air-cooled RMH inside a steel furnace oil tank which is covered in cob.  You can see this build at https://permies.com/t/69632/Building-tube-steel-air-cooled.  Then see the convection oven I added on top of it to utilize the heated fresh air rising from the air jacket at https://permies.com/t/72646/cost-convection-oven-top-steel

My next addition (In the spring) will be a bench as described above,  the purpose of which will be to extract more heat before venting to the chimney.

I have seen barrels used over a barrel stove to steal more heat before it leaves through the flue.

I wonder, if a barrel could be adapted onto the flue exit from a standard wood stove, to act as a bell/strat chamber?
Something like Peterburg's three barrel bell, but using a standard UL approved stove vs an unapproved batch rocket heater.

a bypass could be built in for easy lighting, then close it for the heat cycle.

if a large amount of mass was added to this, a small stove burned HOT could be used to cheat the local bylaws and such.

Brad Hengen wrote:I have seen barrels used over a barrel stove to steal more heat before it leaves through the flue.

not really the same thing as the ones I have seen exit higher than entrance and of course there is no mass.

I wonder, if a barrel could be adapted onto the flue exit from a standard wood stove, to act as a bell/strat chamber?
Something like Peterburg's three barrel bell, but using a standard UL approved stove vs an unapproved batch rocket heater.

There are two difficulties here. The first is that the flue and how it is run is a part of the "UL approved" part. Certainly the permit inspector
will expect it so. Secondly, without mass, the tin stove will get run at an idle because it will be "too hot". The bell will only make this worse
if it has no mass around it... that is if it is only made out of a barrel.

a bypass could be built in for easy lighting, then close it for the heat cycle.

if a large amount of mass was added to this, a small stove burned HOT could be used to cheat the local bylaws and such.

If you used the permit process either you would install as per stove manual and modify after inspection rendering it no longer inspected or
you install lots of mass and end up with a masonry heater which has different rules and probably gets rejected and you remove it.

Better to get a professionally installed masonry heater with bells and or benches that will pass inspection. A proper steel wood stove
will cost as much as $5000 installed properly and a properly installed masonry heater can be as low as $10000 depending on the available foundation.
Oh ya, foundation. Mass requires a foundation to carry the load. This is not that expensive if it is designed into the original foundation or even fitted
later if access is easy. It could be expensive if your floor falls through. Part of the reason for getting a permit is to get a mortgage... mortgage requires
insurance. If you ever use that insurance with a modified wood burning appliance the insurance is void.

So in my opinion, you either do the whole thing non-permitted or you make sure your inspector is happy with what you are doing. If you are able to do
something in a non-permitted context, a rocket stove or masonry heater from the ground up just makes more sense. A masonry heater can be made with
the same number of fire bricks as the rocket mass heater with the rest being clay or home made adobe. So the price if permits are out of the picture is similar
for both. I would suggest the skill level is not that different either.

I have no opinion on which is better between RMH and masonry heater, but Frankenstein heater... not unless you have more skill than average and just like to tinker.

The RMH is actually a subset of masonry heater, with specific combustion core features. It also usually is owner-built with less expensive materials, but this is not a requirement.

Glenn Herbert wrote:The RMH is actually a subset of masonry heater, with specific combustion core features. It also usually is owner-built with less expensive materials, but this is not a requirement.

Yup, I try to stay away from saying the RMH is a masonry heater because there are some people who feel they are a different beast totally. I get less flack  

Len Ovens wrote:

Brad Hengen wrote:I have seen barrels used over a barrel stove to steal more heat before it leaves through the flue.

not really the same thing as the ones I have seen exit higher than entrance and of course there is no mass.

I wonder, if a barrel could be adapted onto the flue exit from a standard wood stove, to act as a bell/strat chamber?
Something like Peterburg's three barrel bell, but using a standard UL approved stove vs an unapproved batch rocket heater.

There are two difficulties here. The first is that the flue and how it is run is a part of the "UL approved" part. Certainly the permit inspector
will expect it so. Secondly, without mass, the tin stove will get run at an idle because it will be "too hot". The bell will only make this worse
if it has no mass around it... that is if it is only made out of a barrel.

a bypass could be built in for easy lighting, then close it for the heat cycle.

if a large amount of mass was added to this, a small stove burned HOT could be used to cheat the local bylaws and such.

If you used the permit process either you would install as per stove manual and modify after inspection rendering it no longer inspected or
you install lots of mass and end up with a masonry heater which has different rules and probably gets rejected and you remove it.

Better to get a professionally installed masonry heater with bells and or benches that will pass inspection. A proper steel wood stove
will cost as much as $5000 installed properly and a properly installed masonry heater can be as low as $10000 depending on the available foundation.
Oh ya, foundation. Mass requires a foundation to carry the load. This is not that expensive if it is designed into the original foundation or even fitted
later if access is easy. It could be expensive if your floor falls through. Part of the reason for getting a permit is to get a mortgage... mortgage requires
insurance. If you ever use that insurance with a modified wood burning appliance the insurance is void.

So in my opinion, you either do the whole thing non-permitted or you make sure your inspector is happy with what you are doing. If you are able to do
something in a non-permitted context, a rocket stove or masonry heater from the ground up just makes more sense. A masonry heater can be made with
the same number of fire bricks as the rocket mass heater with the rest being clay or home made adobe. So the price if permits are out of the picture is similar
for both. I would suggest the skill level is not that different either.

I have no opinion on which is better between RMH and masonry heater, but Frankenstein heater... not unless you have more skill than average and just like to tinker.

I don't think you understood what I meant.

I mean modding a barrel to act like a bell/strat chamber. have it sit above the small stove, tightly surround the small stove with material for a heat sink, and support the barrel.
you'd still have a UL listed stove, unmodified.  
all you doing is really modding the flue with the strat chamber.

As long as the barrel system is sealed, and meets the distance requirements for single walled flue, it would pass inspection.

and with a small stove, you could run it HOT to get heat from the barrel, and to warm the mass around the stove to radiate.

For $10000, I could install a complete GeoThermal system and still save money, then use a Valley Comfort stove as an aux heater when needed.

Brad Hengen wrote:

I don't think you understood what I meant.

Quite possible

I mean modding a barrel to act like a bell/strat chamber. have it sit above the small stove, tightly surround the small stove with material for a heat sink, and support the barrel.
you'd still have a UL listed stove, unmodified.  

Hmm, "tightly surround the small stove" sounds like a modified stove to me, but so long as the new mass surrounding the stove was still the required distance from combustibles you might be fine anyway. So you use this mass also to support the barrel?

all you doing is really modding the flue with the strat chamber.

As long as the barrel system is sealed, and meets the distance requirements for single walled flue, it would pass inspection.

and with a small stove, you could run it HOT to get heat from the barrel, and to warm the mass around the stove to radiate.

I think if the mass was supporting the barrel and then you added mass around the barrel as well you would need to be sure of your foundation. Any mass worth having is going to be heavier than a fridge (or two).

For $10000, I could install a complete GeoThermal system and still save money, then use a Valley Comfort stove as an aux heater when needed.

My experience with Geo Thermal has been less than good. With geo thremal, yes you can spend $10k or less (I am thinking Canadian dollars so a masonry heater may be closer to $7k US as well) but after 10years (or 2 in our case... warranty? yeah right, didn't cover it) it needs to be replaced. With a masonry heater, 30 years down the road you still have a working heater. The firebox may need relining, but if it has been built right, that can be replaced without tearing down the whole thing. Plus the average person with just a little knowledge knows what is in the masonry heater. The geo thermal box.... is a box unless the owner is a refrigeration tech. and it only works when there is power around. I have a 35 year old dryer still working (with minor repairs)... a new dryer would be a 7 year appliance, just like almost all manufactured goods anymore. The 10 years replacement time is the rating for the more expensive commercial products, I suspect the home versions are closer to 7 years mean time to replacement.

When using barrels for the stratification chamber, do they require barrel prep like removing paint, or are the temps low enough that they won't off-gas?

Bryan Paul wrote:When using barrels for the stratification chamber, do they require barrel prep like removing paint, or are the temps low enough that they won't off-gas?

In the end it is your house and you will have to breath whatever fumes it puts off. Buy a canary  and if it dies while using the barrel with paint still on.... maybe get rid of the paint.
Personally, I would remove everything down to bare metal. Coated non-stick pans are designed to be heated and cooked in, but there are enough stories floating around of dead
pet birds from people cooking with them that we have limited our cookware to stainless or cast iron (or even turned steel in the case of one of our woks). It is probably less work
to remove paint first than removing the barrel later and removing the paint and reinstalling the barrel. I am sure that the paint on barrels is not of the high temperature variety
used for exhaust pipes or even engine paint.

Good point Len.  And since stratification chamber RMH designs are so new, maybe I'll have get the numbers myself of how hot the top vs. the bottom gets.

Didn't know where to put this idea, and this thread seems as good as any.

Would it be possible to take Walker's half barrel design and turn it into a pit roast alternative?

Here's what I imagine: the half barrel stratification chamber has a hinged door at the end so you can put in your meat to be roasted; the barrel is covered 8"-10" in cob and then insulated well (something like the easy-bake coffin only with plenty of mass in addition to insulation); the door at the end would then have to be covered in mass as well (could be as easy as berming earth against it). You'd of course  have thermometers in both the meat and the chamber. I'd imagine that you could heat up the mass in about 4-6 hours and the mass would stay sufficiently hot to cook the meat for twenty-plus hours. You'd start the fire around 8 pm the night before, keep it stoked until midnight, and feast the next day at around 6:00 pm. If the inside cooled too much during the night, you could always start a new fire in the morning for an hour or two.

I thought about this after watching some friends pit-roast some pork last spring. It was labor intensive digging the hole, building the bonfire, stoking the fire every couple hours during the night, and digging out the meat the next evening. Plus we used a massive amount of wood.

Most of the labor for this project would be on the front end--building the rmh, but that would be reusable. Aside from that, it's just a matter of berming and unberming the door and lighting and feeding the fire. Feeding the fire would actually be pleasant because you'd get nice warmth radiating  from the bell over the riser--the fire-feeder's seat would probably be the most popular. And it would use far less wood than a pit-fire.

Any problems with this design?

Grant Holle wrote:Didn't know where to put this idea, and this thread seems as good as any.

Would it be possible to take Walker's half barrel design and turn it into a pit roast alternative?

Here's what I imagine: the half barrel stratification chamber has a hinged door at the end so you can put in your meat to be roasted; the barrel is covered 8"-10" in cob and then insulated well (something like the easy-bake coffin only with plenty of mass in addition to insulation); the door at the end would then have to be covered in mass as well (could be as easy as berming earth against it). You'd of course  have thermometers in both the meat and the chamber. I'd imagine that you could heat up the mass in about 4-6 hours and the mass would stay sufficiently hot to cook the meat for twenty-plus hours. You'd start the fire around 8 pm the night before, keep it stoked until midnight, and feast the next day at around 6:00 pm. If the inside cooled too much during the night, you could always start a new fire in the morning for an hour or two.

I thought about this after watching some friends pit-roast some pork last spring. It was labor intensive digging the hole, building the bonfire, stoking the fire every couple hours during the night, and digging out the meat the next evening. Plus we used a massive amount of wood.

Most of the labor for this project would be on the front end--building the rmh, but that would be reusable. Aside from that, it's just a matter of berming and unberming the door and lighting and feeding the fire. Feeding the fire would actually be pleasant because you'd get nice warmth radiating  from the bell over the riser--the fire-feeder's seat would probably be the most popular. And it would use far less wood than a pit-fire.

Any problems with this design?

Most accurate answer is "please test this and let us know how it works"  

I think in this case I would want to use a whole barrel to allow for enough room for food as well as flue gas. The larger size would also allow easier ingress/egress. I assume it is ok that the food is slightly smoked. Assuming the door is on one end, it may be ok for that end just to be insulated well rather than piling dirt there. Mass and insulation on top of the barrel should be more than under and side. (under and side may be ok with mass only, but top might want insulation)

tilt the barrel slightly down towards the door as the bottom may collect water from your cooking and the flue gas as it will take longer for the mass around the chamber to warm up if it is warming up the food mass as well.

if it doesn't work you at least have a nice outdoor heated bench to sit on in the fall... if it does work you can cook in it and still have a nice outdoor warm bench in the fall.

Having played with stratification chamber flue gas heat extraction chambers like this, I personally feel these are much better than the long, long, long and bendy pipe solution. More heat is extracted with less flow resistance.

cook me some traditional Pumpernickel  (cooked overnight in a cooling bread oven, but this might work too.).

Len Ovens wrote:

Grant Holle wrote:Didn't know where to put this idea, and this thread seems as good as any.

Would it be possible to take Walker's half barrel design and turn it into a pit roast alternative?

Here's what I imagine: the half barrel stratification chamber has a hinged door at the end so you can put in your meat to be roasted; the barrel is covered 8"-10" in cob and then insulated well (something like the easy-bake coffin only with plenty of mass in addition to insulation); the door at the end would then have to be covered in mass as well (could be as easy as berming earth against it). You'd of course  have thermometers in both the meat and the chamber. I'd imagine that you could heat up the mass in about 4-6 hours and the mass would stay sufficiently hot to cook the meat for twenty-plus hours. You'd start the fire around 8 pm the night before, keep it stoked until midnight, and feast the next day at around 6:00 pm. If the inside cooled too much during the night, you could always start a new fire in the morning for an hour or two.

I thought about this after watching some friends pit-roast some pork last spring. It was labor intensive digging the hole, building the bonfire, stoking the fire every couple hours during the night, and digging out the meat the next evening. Plus we used a massive amount of wood.

Most of the labor for this project would be on the front end--building the rmh, but that would be reusable. Aside from that, it's just a matter of berming and unberming the door and lighting and feeding the fire. Feeding the fire would actually be pleasant because you'd get nice warmth radiating  from the bell over the riser--the fire-feeder's seat would probably be the most popular. And it would use far less wood than a pit-fire.

Any problems with this design?

Most accurate answer is "please test this and let us know how it works"  

I think in this case I would want to use a whole barrel to allow for enough room for food as well as flue gas. The larger size would also allow easier ingress/egress. I assume it is ok that the food is slightly smoked. Assuming the door is on one end, it may be ok for that end just to be insulated well rather than piling dirt there. Mass and insulation on top of the barrel should be more than under and side. (under and side may be ok with mass only, but top might want insulation)

tilt the barrel slightly down towards the door as the bottom may collect water from your cooking and the flue gas as it will take longer for the mass around the chamber to warm up if it is warming up the food mass as well.

if it doesn't work you at least have a nice outdoor heated bench to sit on in the fall... if it does work you can cook in it and still have a nice outdoor warm bench in the fall.

Having played with stratification chamber flue gas heat extraction chambers like this, I personally feel these are much better than the long, long, long and bendy pipe solution. More heat is extracted with less flow resistance.

cook me some traditional Pumpernickel  (cooked overnight in a cooling bread oven, but this might work too.).

Len.

I really appreciate your advice and design modifications. I'm a newbie at this stuff--I've got one partially built, poorly thought out rocket stove under my belt. Right now, I'm concentrating on learning the science. I've read Ianto's book, and I'm presently reading Erica and Ernie's (great stuff), as well as watching Paul's and Matt's videos (also great). In short, I'm encouraged you don't think my idea is ridiculous.

As I've heard Paul, Erica and Ernie advise, my first real rmh project will be outdoors. With your modifications, maybe this roaster will be my first project. As you suggest, worst case scenario it doesn't work as roaster and I just use it as a butt warmer.

Thanks!

Grant Holle wrote:

Len Ovens wrote:

Grant Holle wrote:Didn't know where to put this idea, and this thread seems as good as any.

Would it be possible to take Walker's half barrel design and turn it into a pit roast alternative?

tilt the barrel slightly down towards the door as the bottom may collect water from your cooking and the flue gas as it will take longer for the mass around the chamber to warm up if it is warming up the food mass as well.

I really appreciate your advice and design modifications.

No problem.

One thing I did think of when I was reading this, The door to the barrel should not be in a gully. When you open it to unload (maybe for loading too), this chamber will not have any breathable air in it. it will rather be filled with mostly water and CO2. Even though they may be quite warm, the CO2 may still be heavier than the surrounding air and not rise. having the land tilt away downwards and allowing a short time for the gas inside to be replaced with breathable air would be a good idea. Being able to deal with the food remotely would be better.

I suppose going farther, if you have a chamber with unknown air quality, you should put a lock on it when not in use for cooking. You do not want a child to decide it is a great place to explore. Normal RMH do not have this problem as there are no man doors in them, so you are treading new territory with something like this underground and open-able.

It would be less of a problem if the whole barrel was above ground if more dirt to move. Having the door at around waist height would make (un)loading a lot easier too. Also look at some of the rocket powered barrel ovens around too. It would make one's butt warming surface a bit high... but having a bed on top of the oven used to be quite popular in Russia, even 5 feet off the ground.

Interesting. I'm wondering, would a stratification chamber bench for inside a house be heavier or lighter than a pebble-style bench?

Shawn Klassen-Koop wrote:Interesting. I'm wondering, would a stratification chamber bench for inside a house be heavier or lighter than a pebble-style bench?

Mass is mass... but, there are a number of other factors that affect things. I don't think comparing to a pebble bench is the best comparison. While a pebble bench is better than a sand bench, I think it is less good than a cob or brick bench.

So the factors that matter are:

how much of the generated heat the mass soaks up.

how thick the mass is, as this determines the surface temperature

How well the mass conducts heat, this affects both of the above

how well the mass is insulated

how well the room is insulated

how well the room contents absorb the heat

However, a stratification chamber does not in and of itself indicate what kind of mass there is. So it would be possible to use one with gravel as a mass. In both the long pipe and the stratification chamber heat collectors, it matters how well the mass absorbs the heat from the flue gas. Then, once the heat has been transferred to the mass the next question is how fast does it travel through the mass. This determines how fast it will heat and how long it will hold it's heat. It also determines what the outside surface temperature will be. In general we want this temperature to be  as low as it can be and still be useful. There are two reasons for this. First is not getting burned by just touching the mass. The second is that hotter surfaces will radiate through walls and windows faster than a lower surface temperature. And of course, the hotter the surface is the faster the heat is used up and the sooner new fuel will need to be burned. The disadvantage to the cooler (but still hot) surface is that it does take longer to heat the living space initially but that is really a heating management problem that can be managed and has been managed for years where high mass heaters are common. (the RMH over comes this to an extent with the exposed barrel for quick heat).

The whole area of room contents and construction are a whole different topic. Any radiating heat source like you mass will radiate right through a window. It may even depend on what is outside the window (a white fence might reflect heat back into the home for example, while a sky view may allow the heat to escape to space) Massive objects in the room can absorb and re-release that heat later. Even the colour of the walls may affect things. Insulation in itself is not always the answer. In the mass heater world, the idea is not to heat the air in the room, but the objects and people instead.

In all the area of heating and how it works really is not well understood. Those who build houses for a living have figured out that if they keep the air at about 21C, their customers will not complain about it feeling cold and the building codes seem to have encapsulated that. However, what the long term healthiest way of both being comfortable and having good air to breath (air tight, one air exchange per hour is not it in my opinion) while not spending an armload of cash or sweat for fuel... is a long way from solved. I think the RMH or other masonry heater is a good start as a heating appliance but to find out the rest will take more research (AKA trial and error). I don't think I can say with any hope of being right that we know how to build good houses. I do think there have been accidental house builds that have turned out well but why they have turn out well is not understood in full. Two people build similar house, one is happy the other not so much. Some of that is what each finds comfortable, but some of it is the many small details that are different from one to the other that anyone examining the houses would not find. Anyway, I am babbling on...

Thanks for your thoughts Len. I suppose I was trying to think about what is the best option for a suspended wood floor. In my head I was comparing Matt's hollow brick bell bench with Paul's pebble style flue bench.

Hi Shawn;
My opinion ... is that even with the brick walls, Matts heater would be lighter.  Some math wizard might be able run the numbers and come up with an estimated weight on the pebbles, bricks are a known weight, cob by volume should have a number...  I can't do those things so i'll stick with my best guess.  

thomas rubino wrote:Hi Shawn;
My opinion ... is that even with the brick walls, Matts heater would be lighter.  Some math wizard might be able run the numbers and come up with an estimated weight on the pebbles, bricks are a known weight, cob by volume should have a number...  I can't do those things so i'll stick with my best guess.  

That's what I was thinking too. Thanks for chiming in!

Official regulations in South Africa and my advanced age work against my actually building an RMH, but I find the discussions and theory fascinating.  Matt solved one problem I had in what to use as the top of the bell and how to support it.  A video of using the rocket principal to heat a clay/pizza oven raised the problem of  a suitable floor which would be self-supporting and withstand all the rigours of high heat.  This, together with Matt mentioning the slabs he has used to cover the bell brought soapstone to mind.  It has incredible properties, attractive finishes, high strength yet can easily be cut and shaped for thickness and fitting available spaces but best of all it can withstand 1000 deg centigrade (2012 F).  It can store heat for extended periods but is also a very good transmitter of heat.  Cooking utensils which prove extremely durable have been made from it for several thousands of years.  Soapstone deposits are widespread in the Appalachian range from Maine to Georgia with significant deposits in Vermont and Virginia and is used for all sorts of ways from high-heat fire places to kitchen cabinet tops, fire pots and cooking utensil apart from its decorative properties.  I would be interested to hear any comments.

Hi John,

Very good idea.  There are conventional stoves that utilize soapstone to store heat.  

Thank you for sharing.

Ag