So there seems to be good responses to my stuff in this forum. So I have another thing to share. (I searched the forum and found some mentions, but no dedicated thread)
I have now attended two rocket mass heater workshops. I have to say that these contraptions are rather amazing. Definitely the next generation of heating your home with wood.
The perks:
Heat your home with five times less wood.
Cleaner, more complete burn.
You can build one in a weekend (I'm about to try an experiment and build one in less than a day)
If you scrounge for parts, you might build one for as little as $20.
The heat from one fire can last for days.
I've mashed all of my notes together into one page on rocket mass heaters (http://www.richsoil.com/rocket-stove-mass-heater.jsp).
Anybody else a fan of these contraptions?
I just don't quite understand how they manage to draw through the combustion chamber, all that horizontal pipe, as well as the four 90s I count in your construction photos.
I don't doubt it works, I just don't get it. Especially considering that people have problems with the draw in wood stoves without having near that degree of resistance in the exhaust.
A light bulb never did appear above my head concerning that. It remains an empty space. Not my head, but the space above it. Okay... maybe both sometimes.
Oh, and how do you clean the firebox of ashes?
Raindog, you are not alone in your puzzlement. I wonder about starting the fire without having smoke in the room aas well as how it can draw around so many corners. ???
I'm the first to admit that I don't have any knowledge about this, BUT . . .
Wouldn't a slow burning fire in all that flue material cause unwanted creasol? Seems like a disaster waiting to happen . . . (?)
/
It's actually a very fast burning fire; that's why it's so efficient and clean. Most of the heat is absorbed by the thermal mass that the flue is typically run through before it exits the building. Our rocket stove-heated cob bench was still quite warm all day today, even though we haven't run a fire in over 24 hours. (It was a sunny day in the 40's, and the house stayed at about 67 with no additional heat..)
A properly designed stove does not smoke at all when you're starting a fire.. Our stove was an afterthought and we were forced to put the whole vertical stack outside. We also run our pipe about 20' through the floor, which is lower than your typical through-a-long-bench run. Those two factors make the stove a little difficult to start every once in a while, but we never have a problem once it's going.
Thanks for continuing to contribute on this forum also, Paul. People here like to learn - and some haven't ever heard of this stuff.
Some like Andrew are already using it though.
How often do you have to feed it, Andrew - Is it a time consuming process?
My stack wasn't tall enough and I wanted the room so I took it out. I was getting downdrafts due to the low chimney. I had to extend it for the Franklin stove too.
I know the fast fire with small dry wood is the key and the creosote becomes part of the fuel rather than coating the inside of the pipes./
Is the open fire inside or outside? It would seem that in order for the thing to start to draw, it would initially have to be warm. If it didn't draw well, then why wouldn't startup be a problem?
I really like the huge amount of cob that is used for thermal mass. Because of how slowly that heats up, it would be fairly easy to control the the amount of heat. Once it gets to the right temp, extinguish your small fire. However, the flip side would be that in order to get it and the house up to temp, you would need to tend the fire for a long time.
Usually, when you go start a fire, the combustion chamber is still a little warm - so there is already a slight draw. But if the combustion chamber is really cold, wad up a piece of paper, light it and toss it in under the combustion chamber. Since it is insulated, that little bit of heat usually gets a little draw going. Then when you start the rest of the fire, the first bit of smoke goes up the combustion chamber (instead of in your face) - and that smoke warms it further.
QuoteI don't doubt it works, I just don't get it.
Which is why the book (http://www.amazon.com/exec/obidos/ASIN/0966373839/rs12-20) is of such great value.
QuoteOh, and how do you clean the firebox of ashes?
It depends on which instructor you have! My first workshop had five instructors so you got to hear some debate on the issue. Some people reach down and pull out a handful of ashes just before every burn. Some like to make a little pit and pull the ashes out every ten burns or so. Others like to shop vac the bottom.
QuoteI wonder about starting the fire without having smoke in the room aas well as how it can draw around so many corners.
:)
Silly rabbit, trix are for kids!
The only draw is in the combustion chamber. It is designed to have a draw equivalent to a 20 foot tall smoke stack fully heated - and then compressed into two feet.
So everything beyond the top of the combustion chamber is a push. So the behavior is more like a dryer vent than a chimney.
QuoteWouldn't a slow burning fire in all that flue material cause unwanted creasol?
I had the same question. And I was directed to a system that had seen heavy use for seven years and told that when they opened it up recently, they found some ash, but no moisture and no creosote. The explanation is the burn is so hot and so complete that after the first minute the exhaust is only steam and CO2.
QuoteOur rocket stove-heated cob bench was still quite warm all day today, even though we haven't run a fire in over 24 hours.
It might even still be too warm to sit on directly. ??
QuoteThanks for continuing to contribute on this forum also, Paul.
Always happy to help out where folks seem to appreciate what i have to share. If there is no objection, i'll try to stop by whenever I have a new video or new article that might be relevant to these forums.
QuoteIs the open fire inside or outside?
Yes.
(sorry, couldn't resist)
Most folks have the feed tube indoors. So while standing over it you can look in and see the flames running away from you.
If you look at my rocket mass heater article, you will see a video or two that shows the feed tube outside.
QuoteOnce it gets to the right temp, extinguish your small fire.
Nobody extinguishes the fire.
The thing is that the mass heats up very slowly. So when the fire needs more wood you sorta think "nah, that seems warm enough" and then you let the rest of the wood burn and then you're done.
The fire is inside.. The flames draw themselves horizontally through the burn chamber. Here's a sketch I found: (http://lh6.ggpht.com/_3ReOSq1TitE/R1jnvDf56eI/AAAAAAAAADQ/c51kX-adous/s512/RocketDiagram.gif)
Even with the lid off of the feed chamber we never get smoke in the house once the fire is going, unless a piece of wood gets 'hung up' and doesn't feed itself, which doesn't happen very often.
We mostly burn Aspen, and we split it pretty small. We feed a couple pieces with about a fist-sized cross section every half-hour or so.. If you pack it full of hardwood it'll go about an hour and a half. Some people are turned off by the amount of attention it requires, but it only takes a few seconds and we're always home. One of those 'not for everybody' type of things, but it seems that most everybody who it IS for like it a lot.. ;) Our neighbor has one of those smokey, expensive outdoor boilers and he's very proud of it.. But he never looks at our firewood pile without saying "Are you sure that's enough?". ;D
Quote from: paul wheaton on January 17, 2010, 01:07:56 PM
QuoteOur rocket stove-heated cob bench was still quite warm all day today, even though we haven't run a fire in over 24 hours.
It might even still be too warm to sit on directly. ??
We've got our flue 7 inches deep, so it takes a full day of burning before it gets too hot to sit on without a cushion. It's usually very comfortable the next morning.. With a few cushions on it it'll stay warm for three days.
Quote from: paul wheaton on January 17, 2010, 01:07:56 PM
The only draw is in the combustion chamber. It is designed to have a draw equivalent to a 20 foot tall smoke stack fully heated - and then compressed into two feet.
So everything beyond the top of the combustion chamber is a push. So the behavior is more like a dryer vent than a chimney.
Gotcha.
Tell ya one thing for sure, it's difficult finding information on rocket stoves from anyone who isn't ideologically invested in promoting and praising them.
Here's my take considering what I could dig up:
Rocket stoves can be a positive and viable alternative in the developing world, where there is not access to materials needed for other firebox and flue run systems and wood for fuel is at a premium, to the widely used three rock fire in an enclosed area, which is highly inefficient and causes major health problems. They can be built with found items and materials and require no great craft to build, and are therefore attractive to those who, out of need or inclination, wish to build for themselves.
Other than that, they suffer all the same downsides, and aren't superior to other wood burning heating systems, which can be of equal or greater efficiency and burn just as cleanly if well designed.
The thermal mass, granted, is pretty darned large, but that's nothing particularly new, as masonry wood burners use mass as well to contain and evenly release heat over time as a rule.
Fair enough, or am I being overly critical? Is that about the gist of it?
Paul, please continue to bring relevant content to the forum anytime you have time to do it.
We have people interested in all sorts of things here... some like alternative, some like conventional, but if they see different ideas even if they don't use them immediately, at least they know and who knows when that knowledge may prove useful. Not having knowledge is more of a problem than having too much.
I was originally invited here to answer questions about my underground cabin, even though most here build above ground, :)
Thanks for taking the time to share with us.
Quote from: glenn kangiser on January 17, 2010, 11:05:14 PM
Paul, please continue to bring relevant content to the forum anytime you have time to do it.
Absolutely. I second that.
Thanks
Andrew, can you post some pictures of yours?
I'm confused as to how a 55 gallon drum with a "plasma reburn section" can hold up to the heat over time. Maybe plasma is not the right term?
I guess that the efficiency of this thing actually comes from the fact that the larger thermal mass sucks the heat out of the exhaust before it exits.
Does it draw very, very heavily?
(Mtn Don, I'm thinking of the firepit at the Rudy's on Carlisle.... I often wondered as to why that does not smoke the place up)
Yeah, I didn't get the "plasma reburn" thing either.. The barrel does get quite hot, but it's not supposed to burn out nearly as fast as your typical barrel stove, since most of the oxygen is consumed by the fire before it reaches the metal. Ianto's is many years old and still cooking. And, it's not exactly hard to replace if it does burn up. ;)
It does draw quite heavily, hence the term 'rocket stove'. It has a bit of a rumble from the flames when it's running good. You can tell when it's time to stoke it just from the sound, even if you're on the other end of the room. The good draw also makes it very easy to start a fire; we hardly ever use kindling. Just a couple small and dry pieces of popple, a half a sheet of newspaper and the rocket takes off. ;D
I'll look for pics.. Not sure if we have any besides what's on the blog.
Couldn't find any new pics besides the construction ones:
(http://www.home-n-stead.com/about/blog_files/page1_blog_entry25_4.jpg)
(http://www.home-n-stead.com/about/blog_files/page1_blog_entry25_3.jpg)
(http://www.home-n-stead.com/about/blog_files/page1_blog_entry25_6.jpg)
The bench looks a bit nicer than this now after drying out/getting the stones cleaned/getting oiled..
We actually gave the stove a little overhaul this past fall. Many of the old bricks we had used were falling apart due to the heat stress, so we replaced them with some firebrick and a chunk of clay chimney liner for the heat riser. We also took out the clay/sawdust insulation we had used and replaced it with vermiculite. Seems to work a little better, but it would have been fine before if not for the inferior brick..
Very interesting. Thanks for the pix. I am amazed by the length of the "flue"!
I wonder if there would be some way to use a small fan in a seperate chamber to assist with starting airflow when the unit is cold.
I'm really intrigued by this. Not a solution for my cabin, but what a neat idea to harvest all that heat that normally escapes up the chimney. I am a little spooked by it though. If the barrel fails, things will get dangerously ugly in a hurry.
Do you have any sort of a way to measure the temperture on the very top of the barrel? I'd be curious to know how hot it gets when it is up and running.
In the first picture, is that your firepit that is well off to the right? What made you guys position it that far away?
Also... how did your family learn about these types of stoves?
Thanks... -f-
Frank I am like you. People used to make oil drum heaters all the time. There was one stacked on top of the other. In fact there was kit's available.
http://www.northerntool.com/webapp/wcs/stores/servlet/category_6970_122+770342+821214
I remember that they (the drums) didn't last that long and they would glow red from the heat. I think it is a really cool idea but if I were building I would have to have a more stable firebox.
Quote from: NM_Shooter on January 18, 2010, 09:14:29 AM
Very interesting. Thanks for the pix. I am amazed by the length of the "flue"!
They say to keep an 8'' diameter flue under 30' long.. I think we are about 27' with 3 90's and a couple 45's... In hindsight we should have put another cleanout somewhere down the line. You're only supposed to have to vacuum the ash out every 5-10 years before it effects the performance of the stove, but we're either going to have to make a very long hose for the shop-vac or cut out another cleanout.
Quote from: NM_Shooter on January 18, 2010, 09:14:29 AM
I wonder if there would be some way to use a small fan in a seperate chamber to assist with starting airflow when the unit is cold.
Like Paul said, throwing a piece of burning newspaper to the back of the burn chamber will usually get it going. Worst case scenario, you have to stick a little burning paper in the cleanout at the base of the vertical stack. It would have been much better if we could have kept the vertical stack inside the house for the most part.. I don't think there would ever be cold start problems. Also, thin stovepipe could be used without any problems, and it would radiate more heat back into the house. We're stuck with a 25' stack outside that should be insulated ideally, and weatherproof..
Quote from: NM_Shooter on January 18, 2010, 09:14:29 AM
I'm really intrigued by this. Not a solution for my cabin, but what a neat idea to harvest all that heat that normally escapes up the chimney.
I'll admit that playing with fire can get kind of addicting.. It's made me a bit of a pyromaniac.. ;D
Quote from: NM_Shooter on January 18, 2010, 09:14:29 AM
I am a little spooked by it though. If the barrel fails, things will get dangerously ugly in a hurry.
Unless the brick structure of the stove collapses, I don't know how it could suddenly fail.. If you go all out and build the whole thing with firebrick and refractory cement it would be pretty foolproof.. If you leave the lid on the feed chamber with just the center hole open for air, even if the draw were to reverse the fire would choke itself out and you just end up with a house full of smoke.
Quote from: NM_Shooter on January 18, 2010, 09:14:29 AM
Do you have any sort of a way to measure the temperture on the very top of the barrel? I'd be curious to know how hot it gets when it is up and running.
No.. We have a copper water heating coil over the top of the stove with a secondary 'lid', so the actual exposed top never gets glowing hot or anything. When it's going strong you can hold your hand about 4'' over the top without much discomfort. Without the water coil it would probably be more like 8-10''
Quote from: NM_Shooter on January 18, 2010, 09:14:29 AM
In the first picture, is that your firepit that is well off to the right? What made you guys position it that far away?
I think that's just the lid to the feed barrel sitting on the ground.. It's in its proper location in the second pic. :)
Quote from: NM_Shooter on January 18, 2010, 09:14:29 AM
Also... how did your family learn about these types of stoves?
I think my mom found them on the internet.. There's more stuff available online now. We built the thing according to this book: (http://www.rocketstoves.com/img/cover.gif)
It's a fun thing to experiment with.. My mom wants one that she can bake in, and I'd like to make one that's more specifically designed to heat water.
Quote from: RainDog on January 17, 2010, 02:47:38 PM
Here's my take considering what I could dig up:
Rocket stoves can be a positive and viable alternative in the developing world, where there is not access to materials needed for other firebox and flue run systems and wood for fuel is at a premium, to the widely used three rock fire in an enclosed area, which is highly inefficient and causes major health problems. They can be built with found items and materials and require no great craft to build, and are therefore attractive to those who, out of need or inclination, wish to build for themselves.
Other than that, they suffer all the same downsides, and aren't superior to other wood burning heating systems, which can be of equal or greater efficiency and burn just as cleanly if well designed.
Oh man, my eyes are rolling so hard I'm getting a headache.
And now my headache is worse because I'm beating my head against a wall.
I had to go outside and count to ten, ten times.
Deep breaths .... okay ....
First, we have two different contraptions. A rocket stove is for cooking food. And while it has been utterly amazing in third world countries, I think it would be equally amazing in any home that chooses to cook with wood. Far cleaner and far less wood.
A rocket mass heater is a different contraption.
Like you said, a rocket mass heater uses a mass. Nothing new there. But there are many things that are new. Things that are not part of any other wood burning contraption. If nothing else, a RMH can be built in a weekend for about twenty bucks. A russian heater is more like a month and at least ten grand.
It is true that the very best designed modern wood stove when used with the draft ALWAYS wide open might be able to come really close to a RMH in cleanliness. But a RMH will keep three to ten times more heat in the house.
So, based on my knowledge, I would have to say that it is my opinion that when it comes to cleanliness, the RMH is generally superior. And when it comes to heating efficiency and startup cost, the RMH is far, far, far superior.
And, I need to point out, that this opinion is radically different from the opinion you conveyed.
Quote from: NM_Shooter on January 17, 2010, 11:26:17 PM
I'm confused as to how a 55 gallon drum with a "plasma reburn section" can hold up to the heat over time. Maybe plasma is not the right term?
When I think of "plasma" I think of molten lava. I suppose I could go and spend some time looking up the word "plasma", but I think if I owned that drawing, I would change that word.
Basically, the two foot tall combustion chamber is insulated and right above the fire. So it gets freaky hot in there. Plus, the smoke and flames and air are getting very thoroughly mixed. Combine the mix and the freaky hot temp and your smoke gets completely burned.
Quote from: NM_Shooter on January 18, 2010, 09:14:29 AM
I am amazed by the length of the "flue"!
Rather than "flue" I usually go with the word "exhaust" or "exhaust pipe" or "duct". After all, at this point it is more like a dryer duct than a chimney.
I wonder what kind of btu's the 55 gal model puts out, and would a smaller 35 gal drum work?
frazoo
I'm not convinced that this isn't a draft dependent burner. If you are able on the next build try building it with a temporary horizontal exhaust below the burn tunnel and see if the fire "knows" where the exhaust is after its warmed up. Here nor there, I'm just trying to understand.
I believe a flame is one form of plasma.
Water vapor aside, smoke is mostly inefficient combustion, unburnt fuel that either didn't have sufficient oxygen to burn or some of the fuel was carried away from the heat before it could ignite. It looks like the reburn chamber is similar to most modern woodstoves, the smoke is mixed with air and given a place to concentrate heat and burn.
Benjamin Franklin invented a downdraft woodburner that was later improved upon and attributed to Charles Willson Peale, "The Smoke Eater". The smoke was returned back through the fire, ran horizontally at floor level, past an observation port, and then to a chimney where it exhausted only warm air.
(https://i180.photobucket.com/albums/x109/windyhilll/smokeeater.jpg)
I think my old Sotz barrel stove is in its 5th barrel and needs a new one, I've been using the door and flue flange for about 30 years, it does go out on jobsites in the weather at times. This one is a single barrel although a shop I rented in the 80's had a double barrel. I don't believe we were getting combustion in the upper barrel. I think if it had a larger intake or an intake on the upper barrel and some form of liner it might burn up there but the heat needs to be able to rise enough to ignite the unburnt gasses. Our second barrel was basically cooling the smoke indoors instead of in the flue. I recall it being a creosote maker. That is the only setup of one I have any experience with though.
I went googling and found this pic of a Hungarian bubos kemence. The white domed structure is the "barrel"
(http://bubos-kemence.freeblog.hu/files/IMG00025.JPG)
But Don for almost instant heat in a unfinished area they were hard to beat. Good shop furnace if you left them wide open. I always remembering to use sand in the bottom of the barrel to reduce them from burning the barrel's out.
I'm hunting for barrel 6 for a reason :)
When you say "draft dependent", do you mean needing a tall vertical stack at the end of the line? Ours does, but I believe that's because we ran our flue so low through the floor. The stove needs a little extra help to push the exhaust gasses down and out. Most flues are run through a bench, and I think at that height there really isn't a need for a vertical stack, other than to get the exhaust out of your face..
When you find that 6th barrel, why not throw together a rocket and test it for yourself? You're a man of adventure.. :)
QuoteI'm not convinced that this isn't a draft dependent burner. If you are able on the next build try building it with a temporary horizontal exhaust below the burn tunnel and see if the fire "knows" where the exhaust is after its warmed up. Here nor there, I'm just trying to understand.
Don, Mine was even with the burn tunnel and to get it over the insulated stack and down the outside then under the cob bench and up to the outside I had a tee with a cap over it near the exit stack to the outside. I would light a paper there then put it into the tee and put the cap over it to start the draft up the stack -- with the cap on then the fire could be started in the rocket stove. This is one method that was described in some of the instructions I read somewhere.
Ernest,
Suppose you went for years heating exclusively with a standard wood stove. And then for years heating exclusively with your RMH.
What do you suppose would be the average number of cords of wood per year with the wood stove?
And for the RMH?
We never used a regular wood stove in this particular house, so it would be pretty hard to say.. It would be interesting to try it and see the difference that the thermal mass makes, what the temperature fluctuations would be like and such. I really have no idea... This house is so different that it would be comparing apples and oranges to make a guesstimate based on the heating requirements of a standard house.
We have about 1400sf of usable, heated space. We've burned about 4-5 logger's chords of aspen (roughly equal to about 7 face chords of maple firewood) in past years. Typically a yooper has to burn from November to May, and longer if long-johns make you itch. ;)
I like that Hungarian bubos kemence, Don. It would be interesting to find out more about how they are built inside -- one of the main problems with the rocket stove that I can see is aesthetics. I was raised with a barrel stove in the house and don't mind their appearance, but for a lot of people, aesthetics are more important than practicality. It looks like it might not cost a whole lot to build one of these Hungarian stoves -- cob could probably be used for most of it, with some firebrick. If you look at this page http://www.buboskemence.hu/gallery.htm , take a closer look at the stove on the left in the top row -- it has a cooking surface as well as an oven, and appears to have a niche on the bottom for storing dry kindling. A very practical design.
http://mek.oszk.hu/02700/02790/html/43.html This page is very interesting. About halfway down the page, in picture number 67, is something I've never heard of before -- an open chimney that runs around the upper part of the kitchen and was used for smoking meat and such!
And here is a description of how to build a bubos kemence: The shape of the ovens (búbos or boglyakemence) in the Great Plain was square or, like hayricks, barrel-shaped or round on top. First its frame is made out of stakes and woven with wicker, then plastered with mud mixed with pieces of sherds. The mouth of such a hearth opens into the kitchen. Its size depends on how many loaves of bread are to be baked in it. Seven to eight large loaves of bread fit into the largest ones, which can occupy a quarter of the room; in the smaller ones there is room for only three loaves. The oven is heated with straw, corn stalks, and, formerly, with reeds. Frequently, in the Great Plain cow dung was kneaded with straw, formed into squares, and dried. This peat (tőzeg) provided a good steady heat. Besides cooking, such a fireplace was used primarily for heating, and a bank suitable for sitting on, ran around its edge, while there was a small nook (sut, kuckó) in its inner corner that served as a resting or often as a sleeping place for children or old folk.
Looks like it could be done easily with cob!
Kathleen (I have a friend here who was born in Hungary, came to this country when he was eighteen -- and is still a bit difficult to understand! I'm going to send the link to this page to his wife.)
Seven examples of the rocket mass heater draw and/or the sideways fire / burn that is an essential component of the rocket mass heater. You can see the fire / flames actually going sideways. And you can see the smoke re-burning and making the rocket sound.
This shows several examples of dry stacked bricks that will eventually be a rocket mass heater core - complete with fire dmonstrating the sideways burn and the draw.
This also shows some clips of the PORTABLE rocket mass heater
http://www.youtube.com/paulwheaton12#p/u/0/a8s-mzfnPy8
Paul,
I'm sooooo interested in these designs! I think I have read everything you've posted and gone to the permies website a hundred times in the last 3 days! We are building a 20x40 1&1/2 story (john's plan) at the moment, and while we aren't quite ready for this step,(We are just drying it in now) I'm really hoping to incorporate this rocket mass heater into our home for our main heat supply!
My question is, we have a pier and beam foundation. We have bigfoot footings and sonotube piers over six feet in the ground along the outside perimeters of the house. (no center support beam) Is there anyway that this rocket mass heater/bench design would be possible on this kind of a foundation?
I am going to be so upset if I can't figure out a way to make something similar to your designs work and we have to get a woodburning stove. We are big DIY type people and I've been dreaming about building/ using cob in my home forever!!! Thank you for your knowledge on this subject and for always sharing it!
Wow, so much has happened since I started this thread. I posted 20 videos to youtube. And then a little over a year ago we had a workshop featuring a lot of new stuff and people asked that I video that. We ended up doing a kickstarter to mash the video onto DVDs. Now over a thousand people have bought those DVDs. Now we're doing more, more and more.
Here's the wood stoves dvds (http://www.woodburningstoves2.com/).
We have a double wide where we put one of the pebble style rocket mass heaters in it. And we have a rocket mass heater put into a tipi (here in montana) and a couple is soon moving into the tipi and gonna tell us how the winter is with it.
We are now experimenting with ideas of being able to move the exhaust through the system faster or slower to further optimize capturing the heat.
To answer the question: yes, you will need to shore up that floor. I think you should go with the pebble style mass because it is lighter. It doesn't work as well as the heavier mass, but it works almost as well. If you go to bed at 72 degrees, with a full cob mass you will wake up to 68 degrees. With the pebble style you will wake up to 63 degrees. Still better than waking up to less than 50 degrees with a conventional wood stove.
Don_P; Those two-barreled (double barreled?) kit heaters have always intrigued me. I prefer the smaller floor loading and looks better than the rocket concept. Always wondered how a stainless steel barrel set-up would work. Comments? http://shop.usedstainlesssteelbarrels.com/STAINLESS-STEEL-BARRELS-DRUMS_c2.htm
.
In fact a small ss barrel might also work for the "rocket mass stove".
I have been interested in rocket mass stoves for a while. One of the problems/fear in the design was starting a fire in a cold rmh and smoking myself out of the house. I figured putting a duct booster in right before the exhaust/chimney goes outside of the house. My dad used a duct booster with his wood furnace for this reason. Any thoughts on this?
Quote from: JRR on December 09, 2013, 05:10:26 PM
Don_P; Those two-barreled (double barreled?) kit heaters have always intrigued me. I prefer the smaller floor loading and looks better than the rocket concept. Always wondered how a stainless steel barrel set-up would work. Comments? http://shop.usedstainlesssteelbarrels.com/STAINLESS-STEEL-BARRELS-DRUMS_c2.htm
.
In fact a small ss barrel might also work for the "rocket mass stove".
Cool, thanks for the SS barrel link, one of those would sure last awhile and look good too, a good source of food grade containers too :) To me the double barrel was a bust, it did produce more useable heat but by cooling an inefficient burn it meant the creosote condensed in that barrel. I didn't get barrel 6, my mason had an old water pressure tank that they were taking out, much thicker walled and close enough in size that it worked for the shop stove. It had a domed top so I had to weld an angle iron square face into it to mount a door on but it should last longer. It was burning down in the shop all day today while I finished up bush hog repairs.
I wouldn't do what Tifflery is proposing, the better way would be to header out that section of floor, go down below and build a footing and foundation to support the mass, a thermal break of high density foam in the floor level could be incorporated. This would keep the weight off the floor as well as keeping combustables out of that area.
I don't see where a rated duct booster would hurt for startup.
Except that there is a lot of moisture that gets created when burning, and damage to the fan motor could result. But you might be able to create a venturi type solution, by using a "Y" in the flue towards the end of the pipe. It would not draw as much as putting the fan inline, but it would protect the fan from moisture.
I think. ;D
We use a small 120 VAC muffin fan as an assist to get the draft going on the wood stove at the cabin. It's outside on the dedicated fresh air intake. Works well and does not seem to impede the air flow once the fire is going.
Down in the barn I've been known to use the air compressor or the output of the shop vac to get the woodstove up and going, it's outside of the heat and creosote but that is really the wrong end to work from. When you pressurize the flue it's asking for a smoke leak or worse. The chimney fans that mount on top of the flue depressurize the flue and use negative pressure to pull the smoke thru, a better way to solve a draft problem. I've seen some paddlewheel type draft inducers that mount partway up the stack but I'm not sure that they are really approved, to my way of thinking they are pulling from below the fan but pressurizing the flue above the fan. I like Shooter's idea, the winds last night blowing over the house chimney had our woodstove going like a rocket a few times.
Don_P & MountainDon: thanks for the input, I defer to more experienced and informed opinions on projects such as these. I have been interested in the use of mass in home heating for a while. I think the experimental rmh, and the heinously expensive masonry heaters may just not be an option for me. I have been considering a masonry/cob enclosure around a fisher (or similar) woodstove may be what I end up doing. Something akin to this:
(http://www.lowimpactliving.com/blog/wp-content/uploads/2009/04/cob-house-stove.jpg)
Well... I tried an experiment with a homemade welded up steel stove one time. The thing was made from 1/4" plate and I stacked bricks around 3 sides of it for some thermal mass, which did help. with the brick trapping the heat I got the sides of it glowing bright several times, enough to warp the plate steel sides a couple of inches. I've read this was the downside of cheap russian stoves as well. The old peasants just used clay and lime, other mass heaters typically use just masonry or heat resistant rock but when they started putting a steel liner in them the steel couldn't take the heat. Cast iron... I don't know, but we do melt metal in masonry. You aren't running a foundry so there's room to see both sides of that. Do remember the metal will move a good bit so allow room for it to expand.
Have you priced a crossfire masonry heater?
And then, in the old days peasants had masonry heaters, the technology isn't new.
I used a duct-booster fan the first winter I was working on our rmh, and eventually soot did clog up the motor. If you're just using it for startup, you'll likely need to remove it from the flue when you turn it off or it'll become a bottleneck in the system. The best strategy for an easy-to-start rocket stove is to keep as much of the vertical stack inside the house as possible (course, that applies to all woodburners..). A cleanout at the base of the stack where you can stick some burning paper gives you a pretty strong jumpstart, if needed.
That stove in the cob-cubby looks cool.. Wonder if that paint is good and washable; we've struggled to find a homemade paint recipe for our earth-plastered walls that can stand up to an aggressive cleaning.
The need for a fan is usually a sign of one of two things:
1) The ratio of heat riser to wood feed is off (if your wood feed is 16 inches tall then your heat riser needs to be at least 48 inches tall).
2) Too much duct. And 8 inch system can deal with about 45 feet of duct, and each 90 degree elbow counts as 5 feet of duct.
Why not just install a fresh air intake? Most masonry stoves have one.
Free online plans with lots of information.
http://dnr.mo.gov/pubs/pub781.pdf
Steel wood stoves and mass heaters have two different designs and don't hybrid very well. For mass heaters concept is to get as fast, hot, and complete of a burn as possible, then extract the heat out of the exhaust gases. For steel stoves, the heat comes out of the initial burn and the exhaust gases are not cooled for safety reasons.
Quote from: Squirl on December 13, 2013, 10:56:32 AM
Why not just install a fresh air intake?
I have one on my rocket mass heater.
Quote
Steel wood stoves and mass heaters have two different designs and don't hybrid very well. For mass heaters concept is to get as fast, hot, and complete of a burn as possible, then extract the heat out of the exhaust gases. For steel stoves, the heat comes out of the initial burn and the exhaust gases are not cooled for safety reasons.
Please meet the hybrid:
http://www.youtube.com/watch?v=DMUES-34Ioc