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are rocket mass heaters "appropriate technology" given the availability of efficient woodstoves?  RSS feed

 
terry jones
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Lawrence Wood wrote:  With an RMH you have a mass of heated material that slowly radiates the heat into the space in a much more localized manner. I don't doubt that you can blow a fan across it to move the air around and heat things more uniformly.  If you are one who likes a uniform heat throughout your house I doubt an RMH would fit your desires. if however you can adapt to having heat in one or two localized places then this is a potentially a good option.


I may have misunderstood what you meant here, but as I read it it does not give quite the correct picture.

IF you meant a RMH may not heat the entire house (due to layout) then ok, yes the heating is certainly not uniform throughout the house. But it seems to read 'there are hot and cold spots within the area the RMH heats' which is not the same as the first interpretation. If you did mean the 'second' interpretation then that I feel is incorrect. Within the area heated by a RMH I think the temperatures are quite uniform which is part of the heating appeal. That is due directly to the radiant heating mechanism, the radiant heat not hitting our bodies and warming us hit the opposite wall, which in turn heats up. IT then becomes a secondary source of radiant heat within the room as it too will then radiate heat to any surface in the room colder than it is. And so on and so on.

The net result is quite the opposite of the 'cold spots and hot spots' that it seems you think. Even the floors are a part of this absorb/emit radiation cycle.

If I did misinterpret your words then apologies.
 
Brian James
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I have a Woodstock Ideal Steel stove, it can burn 12-24 hours (yes, I've documented 24 hour burns on YouTube) and it's an incredibly powerful, efficient and environmentally clean hybrid design that uses both secondary air and a catalytic combustor.

Yet I'm still designing and building a rocket mass heater in my basement, with a bell/bench for mass. I'm building a 6" batch box. I found 18"x9"x4.5" firebrick from the refractory of an old brick factory at a building supply salvage yard for $0.75 each, for the burn chamber and the bench. I'm using a vacuum formed ceramic fiber riser for the initial vertical burn chamber as well as the riser segment and a barrel stove door for the firebox and barrel stove flue connectors for the dual exhaust 6" manifolds on the bottom of the barrel and two 6" inlets into the 2'x6' firebrick bench, and single 6" stove  pipe for the exhaust flue, with an inline flue draft inducer fan on the vertical exhaust pipe to prevent smoke back on start up and speed up start up. I'm designing secondary air inlets just before the riser using channels in the ceramic fiber boards lining the firebox instead of metal pipes or p channels. I'll use white ceramic fiber insulation between the firebricks in the bell and the 2'x2' pavers I'm using on top of the bench, as well as black carbon (welders) blanket material to seal everything. It will be completely modular and moveable.

Am I worried it will burn my house down, smoke back, or fill my house with carbon monoxide? Hardly. Do I think it will burn very hot and very efficiently using the ceramic fiber elements as insulation? You bet, much more than my (excellent) hybrid wood stove.

I will have spent about a third of the cost of my hybrid wood stove in collecting parts for this rocket mass heater build, and expect to use a third of the wood to produce the same amount of heat.

To me it's a fun project that promises great rewards. Do I bring a higher degree of planning, high tech materials, design and expense to my rocket mass heater build than most builders? I can't answer that, but I suspect I do.

Is it "worth it"? To me it is.
 
Davis Tyler
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sounds like a great project, Brian!  Do you have a build thread with some pictures I could see?  Are you planning to run the RMH in the basement at the same time as the woodstove upstairs?  I assume they share a chimney, but separate flues?

I've heard a lot of good things about the Ideal Steel and other stoves from Woodstock.  Matt Walker and I were discussing the stoves on the donkey32 boards, and his assessment is that the stoves are "better than our best for everyday use, in terms of efficiency, emissions, and ease of use" http://donkey32.proboards.com/post/22388/thread
You'll be one of the few people who has run both technologies side-by-side; I'll be interested to hear of your findings.
 
Brian James
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Hi Davis,
I've collected about 95% of everything I need for this build, as well as drawing out the firebox design on graph paper, but health issues have kept me from actually attempting the build. However I hope to complete it in the next two months, so I'll take photos and post a thread. It will be "over engineered" and easy to reproduce with a couple novel concepts included. I got lucky with the 18"x9"x4.5" firebricks though. That's one thing that I doubt can be duplicated.

These are the risers: https://permies.com/t/53413/Inexpensive-vacuum-formed-ceramic-fiber

I was at the wood stove event in DC a couple years ago when I was picking up a Beta model of the Ideal Steel from Woodstock for Beta testing, and met Matt there. I have since picked up one of the early production models of the Ideal Steel. It was a lot of fun being a Beta tester and it's a great stove and great people to deal with.

Right now we're living in my parents' home to help keep an eye on my mom, who is getting forgetful. Her basement has the old hole in the chimney where a Buderus wood boiler used to sit, that we heated with when I was a teen. My brother is going to "borrow" the Ideal Steel while we're living here, but as a Beta tester, I've had a lot of experience with their stoves.
I'd love to see them market a rocket mass heater with their experience with soapstone, which would be perfect for a bench/bell.

Brian
 
paul wheaton
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Josiah asked me a lot of rmh questions a few days ago - as part of addressing a lot of the same stuff brought up here.



More about the Better Wood Heat 4-DVD set.
 
Ivan Weiss
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Having read through this entire fascinating thread, I thought I'd put in my 2 cents' worth. I have never even seen a RMH, much less used one, but since I first heard of them on Permies, I have read everything connected with them and watched every video I could find on them. And yes, someday I want one for my house, plus one for the greenhouse of my dreams.

I have, however, used wood stoves for my primary heat source, for more than 40 years now, most of them in the same house. When I first moved in here, in 1976, I found a fireplace. One of the first projects I undertook was to take a sledgehammer and a crowbar to it, and rip the damn thing out. My buddy and I put in a brick hearth that consisted of a brick pad over the floor and a brick wall with a hole leading to the chimney, for the pipe.

I put in a Tempwood downdraft wood stove. Anybody remember those? They built them in VT of NH, I forget which. They were welded steel, double steel bottoms, bottom and sides lined with firebrick, absolutely airtight, with a round lid in the center of the stove top, and two variable downdraft ports flanking it. These stoves would be totally illegal today, even though the secondary combustion provided by the downdraft effect makes for a far cleaner burn than the conventional "bottom-up" design.

The Tempwood served me well for 11 years. Then I got married. My (now thankfully former) wife demanded a "legal" stove, fearing that our insurance might be canceled. So for $3,500 installed, in came a brand new Vermont Castings "Defiant" model, their top of the line stove, with a catalyst. That made her happy. Still, we went through 3-4 cords of wood in a winter.

Ten years later, she was gone, and once she was, out went the Defiant. I took a sledgehammer and a crowbar to it, too, and hauled if off to the dump. It was a piece of sh*t.  It leaked air, and all the gaskets in the world, and all the gasket cement in the world, couldn't fix it. The verdammte catalysts cost $175 a year to replace, and I was still burning 2 cords of wood per winter.

Out of storage came the old Tempwood, and it has served me faithfully and well ever since. I heat solely with wood, and I have it down to 1 cord again, but here's why I posted in the first place:

#1, I have followed Paul's excellent advice to heat myself first, and the air around me second. I wear layers, even in the house.

#2, My house is insulated to the teeth, with R-48 in the attic, an insulated crawl space underneath, and all my windows double-pane. I don't even fire up the stove till the thermostat (I have electric heat, but try not to use it at all) goes down to 55.

#3, (and this is what I think is germane to the RMH discussion), I scrounge fuel to supplement my purchased cordwood (which I buy every year from a buddy who needs the income). Pallets are free and ubiquitous, downed wood is available, and carbide-tipped sawblades are cheap. Even better are the waxed cardboard cartons that I get from the produce department of my local supermarket. The recyclers won't take them, and if I don't, they go to the landfill. They catch fire immediately, burn with intense heat, and eliminate, entirely, the need for kindling. I have to be careful not to load the stove with them, and only use them sparingly.

Now, in no discussion I have ever seen of RMHs, has the use of waxed cardboard as a fuel source ever been mentioned. If it has, and I have missed it, I apologize. But if it performs so well in a wood stove, why the hell not in a RMH? If the idea is to heat the bricks or the cob, so that the mass will store heat, it seems to me that this would be a terrific feedstock. Certainly that has been my experience. And for RMH use, is it possible that this resource, which now is considered part of the "waste stream," might replace wood altogether? Seems to me that this would be a very "Permie-ish" activity. Thanks to all for a great thread.
 
John Weiland
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@Ivan W: "....in no discussion I have ever seen of RMHs, has the use of waxed cardboard as a fuel source ever been mentioned. If it has, and I have missed it, I apologize. But if it performs so well in a wood stove, why the hell not in a RMH? "

My guess would be that most would want to burn material as close to being produced on their own property and as sustainably as possible.  Waxed cardboard probably would not fit that bill.  That said, I think the topic has come up before.  In general, one could send cardboard to the recycler or burn it for heat as you are.  Just within the last hour, I loaded up the RmH in my garage with all sorts of cardboard, waxed and not, along with raked up detritus like chicken feathers, wood shavings, other odds and ends.  The bell/barrel got to 900 degrees F quickly with that kind of fuel.....and for a quick heat while messing around in the garage, it's a quick die-back on the burn as well.
 
Glenn Herbert
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I think waxed cardboard, if not recyclable, is a fine idea for a fuel; however, I would not want to use it as the principal fuel for a RMH, as the firebox is not large enough to fit an amount that would burn for more than a few minutes. I find that crumpled cardboard, egg cartons in particular, makes an excellent starter for my RMH. I put a handful of finely split sticks on top of it, drop in a burning twist of paper, and have a roaring fire in seconds.
 
Ivan Weiss
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John Weiland wrote:
My guess would be that most would want to burn material as close to being produced on their own property and as sustainably as possible.


Maybe so. Everybody's design is different. In my case, pallets and waxed cardboard are super convenient to my daily rounds, and not only are they there for the taking, but my taking of them is a relief to those who otherwise would have to dispose of them. They serve as an integral heating fuel supplement, and in the case of the pallet wood, as a feedstock for biochar.
 
Ivan Weiss
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Glenn Herbert wrote:I think waxed cardboard, if not recyclable, is a fine idea for a fuel; however, I would not want to use it as the principal fuel for a RMH, as the firebox is not large enough to fit an amount that would burn for more than a few minutes. I find that crumpled cardboard, egg cartons in particular, makes an excellent starter for my RMH. I put a handful of finely split sticks on top of it, drop in a burning twist of paper, and have a roaring fire in seconds.


Thanks. That was my suspicion also, but having zero RMH experience, I defer to those who do have it. Do you see it as an acceptable supplement to stick wood?
 
Devin Lavign
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R Ranson wrote:Which will be best for cooking?  Because I want to cook on my woodstove.  I am considering getting an iron wood fired cooker for my main cooking and RMH for my main heating.


You might want to look into the Walker Wood Fired Masonry CookStove https://permies.com/t/55253/Walker-Wood-Fired-Masonry-Cookstove which is taking rocket stove and rocket mass heater R&D tech and applying it to building a wood cookstove and oven. Even though Walker built this with a black oven (oven open to the smoke path) he wasn't getting much for smoke in the oven chamber due to the clean burning of the design. And of course one can add a white oven (one sealed from the smoke path) in their build.

To bring this back toward RMH topic.

I think something really important I got from this build from Walker was the typical heavy refractory bricks that are being used in RMH might be better replaced with the light insinuative kiln bricks. Walker doesn't get heavy into the topic when discussing it in the videos and write ups, but pouring over the info (since I am considering building one of these for my homestead home) I realized Walker was saying how these insinuative bricks should be used anywhere the combustion fire path is because the typical refractory bricks actually need to be heated up and absorb heat from the fire. Thus reducing the combustion efficiency. This is one of the benefits of cast cores for RMH too from my understanding, cast cores tend to be more insinuative rather than being cold and needing to absorb the heat.

From what I have interpreted from Walker, he is of the mind refractory bricks should be replaced with insulation kiln bricks or a more insinuative cast core in a lot of the RMH. I think this discovery in RMH R&D could help improve RMH efficiency.
 
Glenn Herbert
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It's hardly a new discovery, but it is a relevant observation. I think the reason that insulating firebricks are not more widely used in RMHs is that they are less common than hard firebrick, usually have to be special ordered if you can find a place that will sell them, and cost about twice as much as hard firebrick. Also, being soft, they are not durable enough to use as the hot face in the parts of the feed tube and burn tunnel that are subject to abrasion or impact.
 
Matt Walker
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Glenn Herbert wrote:It's hardly a new discovery, but it is a relevant observation. I think the reason that insulating firebricks are not more widely used in RMHs is that they are less common than hard firebrick, usually have to be special ordered if you can find a place that will sell them, and cost about twice as much as hard firebrick. Also, being soft, they are not durable enough to use as the hot face in the parts of the feed tube and burn tunnel that are subject to abrasion or impact.


I disagree.  My opinion is that if efficiency and performance are your goals highly insulated materials, especially in the firebox, are crucial.  My experiments with many, many systems and my testo flue gas have formed my opinion.  I've tested many hard brick J's, built by myself and others, and they are nowhere near as efficient and stable as they would be with insulation throughout the flame path, in my opinion.  In my opinion, this is new, and the continued use of hard brick and myth of durability is creating a lot of stoves that aren't as good as most box wood stoves.  Thank you for being one of the first to understand Devin.  It's a long road, but eventually we will get folks to recognize.  Thank you. 
 
Devin Lavign
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Glad I seem to have grasped what you were saying well enough you didn't correct a bunch of errors. I was feeling a bit self conscious as you never went into detail explaining it in one go, but rather it was through multiple little bits where you mentioned this and that of why those bricks were used that it started to come together and make sense.

I will be putting it to the test when I build a Walker stove, and when I build a RMH, as I will be using the lighter kiln bricks.

BTW I have been playing around with the Sketchup design (that someone else made) of your stove core trying to figure out a way to give it a hex shape to be in the center of my hex house. Took me a moment to realize why it was so short, it didn't have the cinderblock base. Still a work in progress, but I am thinking I will have the ability to give at least some hexiness to it to mirror the house shape.
 
Matt Walker
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Wonderful Devin, great to hear.  I don't remember who made that sketchup, but I'm no help there.

Folks always speculate on durability, but very few have tried it.  Most rely on what they "know to be true" from reading, not experience.  My point of view on durability vs. performance is that I truly care about efficiency and my neighbors and my footprint, so I choose to have a unit that requires simple, regular maintenance and burns more efficiently than anything else I can afford.  The flip side is a dirty stove that lasts forever.  My tests on hard brick Js put them firmly on par with mid-tier wood stoves in terms of efficiency.  And, since this is the Appropriate Tech thread, that is only efficiency, not emissions, which is never mentioned in these discussions and is the only thing the EPA cares about.  The best new box stoves are still a better choice if you care about emissions, in my opinion.  We have zero particulate data on our stoves, and J's are dirty due to the velocity through the ash bed in my opinion.  We have work to do, no resting on hard brick laurels here.
 
Devin Lavign
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Matt Walker wrote:Folks always speculate on durability, but very few have tried it.  Most rely on what they "know to be true" from reading, not experience.  My point of view on durability vs. performance is that I truly care about efficiency and my neighbors and my footprint, so I choose to have a unit that requires simple, regular maintenance and burns more efficiently than anything else I can afford.


Something I had started thinking when watching your videos on the Walker stove and learning about the kiln bricks you were using was how it shouldn't be impossible to include into the design some sort of sleeve to hold the fire box bricks more prone to possible damage. Since the bricks are insulation, I would imagine one could design a metal sleeve that can hold the bricks in place but be used to pull out the bricks for easy swapping out once they receive too much wear. I am thinking of trying to play around with the idea for my build to see if I can figure out a good way to do it, though I might not attempt it if I can't figure out a good and safe way, since this will be my first build and I don't want to deviate too much from your design and have the stove not work right.

Though I do have to say, about durability, that I agree a lot of folks likely don't have practical experience with these bricks. I have had plenty of experience with them having done ceramic sculpture in my past. I have seen these bricks hold up pretty well after repeated ceramic explosions in kilns. I would liken the hard vs soft bricks to the reed vs the tree. While one would say of course the tree is stronger and more durable, the reed can withstand wind storms the tree can not due to the reed being flexible. Similarly the hard bricks are more brittle and impacts can cause them to crack and break easily, while the light bricks are softer they can actually take a lot of impact with just minor scuffing damage done to them. This is not to say the lighter kiln bricks will last as long as the hard bricks in a fire box, but their durability is I think underestimated.
 
Matt Walker
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I don't think you need to worry about a sleeve or anything.  The stove is extremely easy to service, and the bricks in my original build are fine.  I don't even live there anymore, and I didn't train the people who do with any special advice.  They are stuffing wood in that thing daily, like I did for almost two seasons prior to this, and the fire box isn't even close to needing service.  The bricks have barely lost any thickness, just a slight depression on the "cheeks."  Better durability than any firebrick core I've ever seen.  They all crack, and then are loose, in my experience.
 
Devin Lavign
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I am not worried about the bricks in the short term, 5-10 yrs, more thinking a decade or more down the road how having a sleeve might be helpful to replace them. Though as I said, since this will be my first build unless I can figure out an easy safe way to add a sleeve, I might not even attempt to experiment with it. I have faith in your design, and don't want to mess with it too much without 1st hand experience with it to give good practical knowledge on what might be improved or should be left as is.

Yes, the hard bricks are a lot more prone to cracking and chipping. That is the trade off of being harder, they are more brittle.
 
Glenn Herbert
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Thomas Rubino described a very bad experience with castable refractory feed tube and burn chamber, but I don't know how he actually treated it aside from heavy daily use burning numerous cords of wood in a season.

My own J-tube is castable refractory (Heat-Stop 50), and after a month and a half of use has developed several cracks, but is holding up fine. I do have a steel sleeve insert for the P-channel air supply which eliminates abrasion at the feed mouth.

I think the reasons insulating firebrick is not widely used are as I said; I do believe it is likely to be much more efficient and people would be well advised to use it unless they have gorillas feeding the fire I think even having the top bricks at the feed tube mouth as hard brick would prevent most abrasion.

I have built an L-tube bake oven and a J-tube cookstove entirely of cob (the L-tube has fb splits on bottom and sides of the feed mouth), and both of them after moderate use are still in fine shape. My all-cob pottery kiln has fired itself very hard, and I expect a perlite-clay riser and even burn tunnel would do likewise. The feed tube top will never get hot enough to fire to pottery at the exposed top edges, though.
 
Matt Walker
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Regular maintenance is a part of being a stove operator.  If you get to the end of the season and haven't done your maintenance, you are going to "describe a very bad experience."  I didn't change the oil in my car for 100,000 miles and can describe a very bad experience.  Are cars not durable enough?

Glenn, you could experience 30% more efficiency with insulated fire brick in my opinion.  I accept that some will choose dirty durable stoves, but I believe it is important to share that we have a choice.  Insulated builds are the way forward if we want to improve things for our neighbors and ourselves.
 
Glenn Herbert
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I fully support insulated firebrick or insulated castable use. My J-tube is only 1 1/2" of castable, not insulated in itself, but not nearly as dense as hard firebrick, and heats up immediately when I start the fire. It is surrounded by 3" thick insulated firebrick from a derelict kiln. My riser is a very light perlite-clay mix.

By the way, Thomas said that he repeatedly relined his feed tube (I think with castable), but it still kept breaking down from abrasion. Personally, I can't imagine mine acting like that, but I tend to be quite gentle with loading.
 
John Harrison
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Matt Walker wrote:

Glenn, you could experience 30% more efficiency with insulated fire brick in my opinion.  I accept that some will choose dirty durable stoves, but I believe it is important to share that we have a choice.  Insulated builds are the way forward if we want to improve things for our neighbors and ourselves.


Hi Matt - I was planning to build a 5" batch rocket using 25mm (1 inch) thick hard firebrick splits backed up by 20mm ceramic fibre insulation. I'm hoping that this combination of hard but thin and well insulated firebox components will provide the best of both worlds as regards durability and performance.
What do you think?
 
Jessica Johnson
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Thank you for this topic.

I would like some hard numbers on what the average emissions are for RMHs versus wood stoves that have been built to the EPA's current standards. The closest I've seen so far has been "This Youtube video shows little visible smoke." If there are calculations to be made, I'm good with a calculator, but I need the results of good tests taken from samples of both RMHs and modern wood stoves. (That is, I need raw numbers to plug in.) Does anyone have anything like that?

Thank you.
 
paul wheaton
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Jessica Johnson wrote:I would like some hard numbers


Like this:



More in this thread.
 
paul wheaton
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Jessica Johnson wrote:I would like some hard numbers on what the average emissions are for RMHs versus wood stoves that have been built to the EPA's current standards. The closest I've seen so far has been "This Youtube video shows little visible smoke."


For those of us that are keen on rocket mass heaters, you start with how you are heating your home with one tenth the wood. Right off the bat, that suggests that there will be one tenth the emissions. 

Next is that when we are in the middle of a burn, the emissions are so clear and virtually odorless.  This suggests that during the burn, we are burning cleaner. 

So it seems that when comparing to "wood stoves that have been built to the EPA's current standards", a rocket mass heater has, at worst, one tenth of the emissions.  Probably much better.  Therefore, it is worthwhile to proceed.

Naturally, it seems that if the government is going to throw around billions on energy stuff, it makes sense for them to do some serious number crunching in this space. In the meantime, I think the difference is so profoundly positive, quite a few people are thinking "good enough for me!"




 
Rob Griffin
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Bored and trolling around and found this interesting thread.  I think Lawrence brought up a good point about the hot and cold areas causing mold problems.  I remember reading, or maybe it was on a podcast, that Paul's Fisher Price House had mold problems even in dry Montana because of the hot/cold areas and it even made Jocelyn sick.  Has anyone else experienced this?  Do you need another dry heat source in the house?  How do you combat this?
 
paul wheaton
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A video that josiah made of me talking about criticism of rocket mass heaters.  The video was recorded about four months ago, but josiah released it this morning.



 
Joshua Myrvaagnes
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It would be great to have numbers on this thread, for anyone reading through this--translation into layperson's English from the chart.  Anyone?  I will go look at the other thread and if I can understand it I will re-post here. 

It makes sense that 1/10th the wood would imply 1/10th the emissions.  Then the question for New Scientist is the comparison with "district heating"  I just found out we actually have that in America!  that we have power plants in Boston and Cambridge and NYC!  I thought they were trivial relics, but apparently their "excess heat" is used to heat a good 1/2 of the city.  But what is the real cost in emissions of building, maintaining, building filters for, etc. those plants vs. every house having its own rocket mass heater??  These numbers would be valuable for the broader discussion of bulk systems vs. individual responsibility/independence.

Thanks geniuses!




paul wheaton wrote:
Jessica Johnson wrote:I would like some hard numbers on what the average emissions are for RMHs versus wood stoves that have been built to the EPA's current standards. The closest I've seen so far has been "This Youtube video shows little visible smoke."


For those of us that are keen on rocket mass heaters, you start with how you are heating your home with one tenth the wood. Right off the bat, that suggests that there will be one tenth the emissions. 

Next is that when we are in the middle of a burn, the emissions are so clear and virtually odorless.  This suggests that during the burn, we are burning cleaner. 

So it seems that when comparing to "wood stoves that have been built to the EPA's current standards", a rocket mass heater has, at worst, one tenth of the emissions.  Probably much better.  Therefore, it is worthwhile to proceed.

Naturally, it seems that if the government is going to throw around billions on energy stuff, it makes sense for them to do some serious number crunching in this space. In the meantime, I think the difference is so profoundly positive, quite a few people are thinking "good enough for me!"




 
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