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rocket mass heater uses less wood than a wood stove  RSS feed

 
master steward
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Location: missoula, montana (zone 4)
bee chicken hugelkultur trees wofati woodworking
 
                        
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Location: Iowa, border of regions 5 and 6
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Cool! (as one of the YouTube commentators noted  )  This brought up a thought (and please forgive me for writing out loud   ):

Monolithic concrete domes (MD) may not fit into the traditional "permaculture" thought; yet their energy efficiency and safety appeal to me.  (Safety means never having to worry about a tornado ripping your roof off.)  One reason they're so energy efficient is that the mass of all that concrete acts as a "thermal flywheel".  Most people I've spoken with who have MDs say they don't have to run the heater until March or April, and don't have to turn on the air conditioner until August. 

What you've described in the rocket mass heater being "cool" in the summer is that whole thermal flywheel effect.  Cob is a not-good insulator -- R=0.5 -- while it's an excellent thermal mass, which is why the RMH works so well.  Heat always flows "downhill" from hot to cold.  When the RMH is in use the heat from the exhaust (smoke + water vapor + combustion products) flows into the metal stovepipe and from there into the cob.  However, the reverse process is also true.  During the summer, if the stovepipe is COOLER than the surrounding cob, heat is going to flow from the cob through the stovepipe into the air in the stovepipe, and out through the chimney.

So if you can keep direct sunlight off the cob of the RMH, you have the potential for a "poor-man's air conditioner."  The question is: do you need to keep the opening to the RMH unsealed for this to work, or does it need to be only MOSTLY sealed, allowing only enough air through to keep circulation going within the stovepipe?
 
paul wheaton
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I think I would just leave it unsealed.
 
                          
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Location: Hay River NT Canada
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Dear Paul,

I'm so glad to see you found and love the rocket stove, it is very brilliant. Something I've be milling over is an idea of building a rocket mass chimmey over a spot that would hold anila wood gasification stove? Then we could have carbon negative stored heat....
What do you think, could it work, could there be enough draft to pull the heat?

Digging
 
paul wheaton
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digging wrote:
Dear Paul,

I'm so glad to see you found and love the rocket stove, it is very brilliant. Something I've be milling over is an idea of building a rocket mass chimmey over a spot that would hold anila wood gasification stove? Then we could have carbon negative stored heat....
What do you think, could it work, could there be enough draft to pull the heat?

Digging



I'm afraid that a lot of what you have just said confuses me.  Perhaps you could start a new thread about your idea?

 
                            
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Any time you get a stove with >83% efficiency, you will have condensation of the water vapour in the flue gas.  This condensate is quite acidic and will eat through regular vent pipe in probably a couple of years (probably less for the rocket stove since I image the condensate would sit at the bottom for long periods).  Even in concrete or brick chimneys, this can lead to spalling.  Have you come across any indications of how this stuff reacts with the Cob?  Might make for some improved designs allowing for easy replacement and/or improved materials in the vent pipe...
 
                  
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What exactly is the difference between a rocket mass stove and a conventional masonry heater? Just so there's no confusion, by "conventional masonry heater" I mean of the type that burns wood ferociously at smething like 1100deg F and stores the heat in the masonry body of the heater.
It seems that the rocket mass stove is a simpler cheaper to build version of the traditional masonry heater?
 
paul wheaton
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My impression of the masonry heaters is that they don't burn that hot.

The rocket mass heater can push exhaust downward.  The masonry heaters need to have a constant upward path.
 
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As i understand it, The rocket and the mass rare two different adjectives for the stove.  You can have a rocket stove without thermal mass, and you can have a thermal mass heater without a rocket design.  The rocket mass stove combination is great because, as Paul said, the force of the exhaust allows you to form the shape of the thermal mass as you like.  It would be very difficult to have a conventional masonry stove in the shape of, say, a banquet bench.
 
                  
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My impression of the masonry heaters is that they don't burn that hot.

The rocket mass heater can push exhaust downward.  The masonry heaters need to have a constant upward path.



Maybe it's just a terminology thing. Here is part of the MHA (mansonry heater assoc. of north america http://mha-net.org/ ) definition:

the gas path through the internal heat exchange channels downstream of the firebox includes at least one 180 degree change in flow direction, usually downward, before entering the chimney



I have seen many "masonry heaters" and some are quite creatively constructed with bench flues for sitting on etc.
It was only after visiting this website that I learned of "rocket mass" stoves.
I have also heard of masonry heaters of this type called "Russian/Finnish stoves".

Typically, traditional masonry heaters are very expensive to have constructed as they require skilled trades people and special high temperatre fire bricks. Even pre-fab heaters cost a bundle. I take it that the rocket mass stove is not so expensive to construct?

Masonry heater links:
http://www.alternativeenergyprimer.com/Masonry-Heaters.html
http://www.vermontwoodstove.com/msnyhtrs.htm
http://www.youtube.com/watch?v=fbRi8XROncM&feature=related

p.s. How do I embed a video in my post? Sorry if that's a silly question.

Edit:
 
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I just finished reading The Book of Masonry Stoves - Rediscovering an Old Way of Warming by David Lyle, borrowed from my local library system. Excellent book detailing the history of Masonry stoves and their basic theory. I can't recommend it enough.

For those people who already have an iron/steel woodstove and don't wish to risk ripping it out for an experimental cob rocket stove, (or have the time to take on such a project) here's an idea: stack a bunch of thermal mass around the old iron woodstove. This thermal mass could be old bricks, stones, a cob wall, jugs of water - anything that would absorb and then re-radiate the heat.
 
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Location: Missouri Ozarks
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I'm building a house on piers.  That ruins it for me using a mass heater doesn't it?
 
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awhitaker wrote:
I'm building a house on piers.  That ruins it for me using a mass heater doesn't it?

why are you building it on piers and how high?

if you're just going to have a crawlspace you could put most of the RMH in he crawlspace and let it warm the floor.

on the other hand if you're building on piers out over the river to keep you place above flood level there is very little you can do and you will lose heat through the floor
 
Alan Whitaker
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I'm on the black lands (clay)of NE TX.  The soil moves, expands and contracts depending on the moisture.  Right now, I have 3" cracks everywhere and in the winter, there will be none.  Every house here that is built on slab, has foundation problems.  On piers, I can level myself as needed. 
I won't block the air circulation under the house because we have a much harder time cooling, so I want the air flow in the summer.  I'm actually building a modified dogtrot house.  Cooling is my main concern.  Heating is easy, but I would like a more efficient way to do that.
 
Brice Moss
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I'm a bit curious as to why airflow under the house would be good for summer cooling, I'm trying to work the airflow in my house to pull cool air up from the basement in the summertime, and cant imagine that a hot breeze under the floorboard would make things cooler inside
 
Alan Whitaker
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If I were using an air conditioner in a house without a vapor barrier on the floor, I would want it sealed.  But I want it dry under the house.  I want that air to be able to move just like I would in a conventional house with an attic.  With our high humidity and hot weather and no air conditioning, sealed anything seems to be inviting problems with mold and mildew.  I know I have used whole house fans to cool down at night and my leather boots turn green from the high humidity. 

The old houses in the South had high ceilings, hollow walls and were unskirted.  Many that I've seen had vents in the bottom of the walls that allowed airflow from under the house to the attic where it was vented out.  You can get in the attic of some of these houses today and feel a slight draft of the air on its' way up and out.  That is if the house has not been "remodeled".   But people in the South have been building houses like they do in the North and it does not work without air conditioning.  And I hate spending money on electricity.  I do it, but I don't like it.
 
Brice Moss
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cool info/concept thanks for sharing
 
paul wheaton
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Old hammy wrote:
p.s. How do I embed a video in my post? Sorry if that's a silly question.



It's a bit of a hack I made, but I gave instructions in the "tinkering" forum.
 
                  
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Thanks.
 
gardener
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kind of but not totally. a RMH can be built for about $50.00 if you scavenge the materials. it has a radiant part and a thermal mass part making it better for those who have no patience and we dont have the constraint of needing an upward path for the exhaust. makes for a more versatile design. a couple other differences are the temps, way the stove is run, air control, space considerations, and method of warming the body, skill of builder, time required &c.  I would not say its better than a masonry stove for all purposes but its good at what it does.

Old hammy wrote:
What exactly is the difference between a rocket mass stove and a conventional masonry heater? Just so there's no confusion, by "conventional masonry heater" I mean of the type that burns wood ferociously at smething like 1100deg F and stores the heat in the masonry body of the heater.
It seems that the rocket mass stove is a simpler cheaper to build version of the traditional masonry heater?

 
                      
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Hi! I'm a newbie doing research on enriching my exhistance. Im so THRILLED at the wealth of information you have generously shared. Thank you. My question is-is wood the only fuel that can be burned in the RMH? Could other materials like Dried Pete Moss burn as well? I only ask since I want to avoid burning my trees & if I use Sphagnum Pete Moss as a living water filter for my stored water harvesting system- is there any reason it cant be harvested dried and bunred as well thereby also multitasking with that resourse? Are there other fuels that are acceptable to burn? Pellets, compressed straw bricks, etc? Thank you again for you time & consideration.
 
Ernie Wisner
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I dont see how the moss would be effective unless it was pressed and dried as briquettes.
having never tried i cant really say definitively; However i do know peat-moss is the very devil to dry.  peat (the black stuff out of the deeper bogs) might work if you cut blocks and let them dry over time. I think store bought wood pellets would work if you can get the feed and air right. Our experiments with briquettes so far are favorable so i would assume that a pressed straw brick would would work if the density was right. the stoves are very good on fuel so most of what we burn is pruning, Fallen branches, and coppice wood.  I have gotten an oil drip to work but thats about the extent of my experiments to date. hope this helped.
 
                      
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Thank you. I really don't have any true knowlege of burning Pete Moss. I've only heard that its burned a great deal in the British Isles. I just thought if I took an old hand turned cider press & squeezed the moisture out then let it dry- perhaps it might work. Is it the density of a material that affects the value of the burn or is it just a matter of the material fitting in the fuel shoot? I know folks that densly pack toilet tissue tubes with dryer lint to make poor man presto logs & fire starters but am not sure of the amount of residual material that would be left to clean out later or if the lint would leave a film on the insides of the ducting like a creasote coating, or the fumes that might potentially be expelled... I know many campers that use chunks of dried moss as fire starters when camping but it seems to me that if you're a tourist/city kid & you pick up the wrong moss you could end up with poison gas from your fire. Is there any literature or resourse knowlege on the topic?
 
Ernie Wisner
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peat moss certainly.  Dryer lint, i dont know. moss burning with poison gas, not that i have ever seen. A rolled up news paper works better for a poor mans presto log.

yes fuel density is written about in many places that give information on wood and solid fuel burning. Also most briquette web sites have density comments. You will have to experiment with fuels for a RMH (outdoors). let us know your findings please.
 
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