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stratification chamber for a rocket mass heater  RSS feed

 
master steward
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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




 
Mother Tree
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Awesome!

Matt has a slightly longer video discussing similar material - rocket mass heater Bells and Benches Discussion

 
pollinator
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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.
 
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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.
(24)-Final-coat-of-clay-paint-project-completed-and-fully-operational..JPG
[Thumbnail for (24)-Final-coat-of-clay-paint-project-completed-and-fully-operational..JPG]
(26)-Old-BBQ-body-is-now-a-convection-oven-on-top-of-RMH-bell.JPG
[Thumbnail for (26)-Old-BBQ-body-is-now-a-convection-oven-on-top-of-RMH-bell.JPG]
 
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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.
 
Len Ovens
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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.
 
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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.
 
Len Ovens
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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 
 
Brad Hengen
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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.

 
Len Ovens
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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.

 
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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?
 
Len Ovens
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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.
 
Bryan Paul
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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.
 
Ruth Stout was famous for gardening naked. Just like this tiny ad:
What would you cook first in a rocket oven?
https://permies.com/t/89866/cook-rocket-oven
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