rocket mass heater uses EIGHT TIMES less wood than a wood stove

Started by paul wheaton, August 14, 2010, 08:53:31 PM

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John Raabe

There have been a number of posts and experiments with rocket stoves that have been reported on this site.

Here is a link to Glenn's project from 2006.


http://countryplans.com/smf/index.php?topic=2350.0
None of us are as smart as all of us.

PapaBear

Great discussion on rocket stoves.  I think this is the second or third time I've watched some of Paul's videos as I've been reading up on this for a year or so.  I'd like to build one to heat my shed/workshop if I can ever finish all my other projects.  I don't have any first hand experience, but I can share what I've learned from reading.

On the creosote issue, my understanding is that in a rocket stove the fire burns hot enough (600+) and long enough (through the cob whatever) to effectively eliminate (burn up) any particulates in the exhaust.  Therefore you get a more efficient burn (is this the 75% vs 90% efficiency thing?).  In other stoves (conventional wood stove) the fire and heat is less contained so a lot of the combustion heat is lost and the fire just never gets hot enough to burn everything.  I think this is similar to why pellet burners are labeled as more efficient, because they contain the combustion better (I've got no source on that other than my own interpretation of what I've read).  Along these same lines, it makes sense to me that increased efficiency (less leftovers in the exhaust) would lead to a safer system.

The other advantage I think rocket stoves have is more efficient retention of heat.  When the exhaust is snaked through a cob something-or-other more useful heat is retained.  I think a typical wood stove relies more on air convection (very low thermal mass) to heat a space than it does conduction and radiation as in a cob bench.  Similar to why radient heat flooring is more efficient at overall BTU retention than a heat pump (makes sense intuitively anyway).  As for the safety issue, in what I've read there is often guidance to make sure you can clean ALL of your ductwork out, cause it'll need it eventually.  

So, I guess the way I think of it, heating stove efficiency is two-fold.  One, completeness of burn or how many BTUs can you recover from the wood itself; and two, how many BTUs you can recover from your exhaust and get into your space.  It seems to me that a rocket stove with cob bench wins on both accounts.  (remember, no experience here, only book knowledge)

PapaBear

EDIT: 1st post!?  I've been lurking for so long I didn't even realize I've never posted   ::)  Hello from Maryland!


Squirl

 w* Papabear. I'm glad you finally joined the discussion.

There seems to be a nomenclature issue.  The "rocket stove" I am a big fan of.  
http://www.iwilltry.org/b/build-a-rocket-stove-for-home-heating/
These work like a regular wood stove, only hotter and faster.  They get a large amount of the energy from the wood, and vent the exhaust safely.

It is the "rocket mass heater" seems like a more efficient, yet unsafe alternative.

Quote from: PapaBear on September 14, 2011, 11:21:55 AM
 As for the safety issue, in what I've read there is often guidance to make sure you can clean ALL of your ductwork out, cause it'll need it eventually.  

I guess this is one of the things I haven't seen.  All I have seen are limited access to clean out ashes from before and just after the combustion chambers.  Also most seem to have pipes snaked under benches and through cob, that you would have to break the cob to clean the pipe.

Ernest T. Bass

You make a lot of good points MD; those reasons are why the stove really isn't for everybody. I would never put one in an occasional-use cabin/home. Heck, it might even take days to heat up! And I'll have to admit, I really like to be able to watch the fire--my biggest pet peeve of the traditional-style rmh. The heated bench is super luxurious, but being able to lay back on it and watch the fire would be even better! I've been throwing around lots of ideas for a window.. Trouble is how hot the burn chamber gets. It would have to be placed so the flames were getting sucked away from the glass..

Squirl, cleaning isn't any different than any other masonry stove. Lots of cleanouts. Sounds like a pain, but you rarely need them.

Our family's homestead adventure blog; sharing the goodness and fun!

MountainDon

I had something happen when I was huuriedly modifying the post ETB refers to above. I lost the whole thing.

What I was commenting was that I had no interest in a rocket mass heater myself. Our cabin sees 2 to 3 days use at a time in the cool/cold weather seasons. A RMH would be next to useless as it would take very long to warm up itself and then the cabin interior. In the coldest weather even if the RMH came to temperature while we were there, then in the nearly 2 weeks before the next use everything would most likely return to the ambient temperature.


I also added a personal note, that I would actually like to burn more wood that we do now rather than burn less. When thinning a forest as we have been doing we find ourselves with more wood than we can even give away. Some folks express interest then back down when they realize they'll have to drive 60-70 miles to pick it up. Free is free so I don't understand those folks. Right now we have a couple cords of seasoned pine ready to go. Plus another several of 3 to 4 foot lengths of freshly cut pine. And some folks are picky when they come to get their free wood; they leave the 3 inch and smaller behind. I don't ask them back.   Anyhow we end up burning up piles of it over the winter in bonfires so as to reduce the fire danger. Maybe some day in the distant future we will run out of trees to thin. But then I'm going after the neighb ors lands. They would like to see their trees thinned, but never get around to it and are too cheap to hire out the work. I'll do it for free after we're done just to keep busy and slowly beat back the fire danger on theiur lands that abut ours.
Just because something has been done and has not failed, doesn't mean it is good design.


MountainDon

ETB, re the window..... The flames on our Aspen with window in the door actually lick towards and up over the glass as the air flow is up the front and then back in the secondary burn chamber.  Good quartz glass should do the trick.   ???

Just because something has been done and has not failed, doesn't mean it is good design.

paul wheaton

I just finished a major overhaul of my rocket mass heater article.  Nine new drawings, one new animation showing the path of the fire/smoke/steam, new videos and twelve new pictures.

http://www.richsoil.com/rocket-stove-mass-heater.jsp



Ernest T. Bass

Really great page, Paul.. One of the most comprehensive collections of info on the web.

Our family's homestead adventure blog; sharing the goodness and fun!

paul wheaton

I posted this video about ten minutes ago.

After building 700 rocket mass heaters, this is Ernie and Erica's
latest.  They are in the okanagan highlands where snow has been on the
ground, non stop, for months.  Two days earlier the temperature
dropped to 19 below.  They show how little wood is needed to stay warm
up there.  And they show some new innovations with their designs.

http://www.youtube.com/watch?v=4usXIAoy9us



rick91351

Proverbs 24:3-5 Through wisdom is an house builded; an by understanding it is established.  4 And by knowledge shall the chambers be filled with all precious and pleasant riches.  5 A wise man is strong; yea, a man of knowledge increaseth strength.

umtallguy

have any of these been in use for long enought to see real safe lifespans on the combustion chambers? the thin walled barrells scare me

paul wheaton

There are several that are ten years old or more and still getting regular use. 

I have heard of folks replacing a worn out barrel.  My dusty memory is suggesting that the barrel lasts about seven years.  But the concerns are not like the concerns you would have for a conventional wood stove because the design of the rocket mass heater is such that leaks are not as scary.  With a proper heat riser the exhaust is almost all steam and CO2. 

The key is that this contraption is a very different animal from a conventional wood stove.  The key to it all is the heat riser, which is designed to basically maintain a chimney fire for the whole burn. 


Ernest T. Bass

Nice vid, but I was a tad disappointed to not get some design/construction advice from people who seem to have so much experience...

Our family's homestead adventure blog; sharing the goodness and fun!

umtallguy

hmm that video is really interesting, I was expecting there to be some pressure in the stove, but i guess when it is drafting it actually is sucking down on the lid holding it in


paul wheaton

A video that has all of the information would be a full two hour video.

I have other videos that have more information on the "how to" aspect.  And then there is a book.  Recently, Ernie and Erica have released VERY detailed plans for an 8 inch system and a 6 inch system.  http://www.permies.com/wood-burning-stoves.html




Ernest T. Bass

Yeah, the basic info is readily available and any of us who are serious about these things already own the book.. I just meant that if you are going to bother interviewing someone who's built hundreds of these things they must have a few new ideas to share. ;) Not intending to harp on ya', just pointing out that I like it when your vids are more informative, that's all.

Our family's homestead adventure blog; sharing the goodness and fun!

paul wheaton

Ernest,

I hear ya.  And I have something you are gonna love.  Actually, I have a few things you are gonna love.

podcast 019 - rocket mass heaters

podcast 104 - rocket mass heaters

Both of these are with ernie and erica.  And we go into gobs of detail.

And there's more ....

Erica has drafting skills and has wrapped hundreds of hours into extremely detailed plans along with detailed builders notes:

Wood Burning Stoves 2.0

If you sign up for my daily-ish email you would hear about all their new stuff as I hear about it, and all sorts of similar stuff.


Ernest T. Bass

Thanks for the links, Paul. Those two really know their stuff. Listening to you guys talk about the stoves makes me want to play with fire more and build another one... We want to build a sauna/summer kitchen, and I really want to make a rocket cooker with an oven that also heats water in its spare time... Tall order.. I keep drawing designs up. I also want to do more experimenting with radiant floor heating.. Got the bug. ;)

Our family's homestead adventure blog; sharing the goodness and fun!

KLF

Quote from: Ernest T. Bass on February 25, 2012, 01:02:05 AM
Thanks for the links, Paul. Those two really know their stuff. Listening to you guys talk about the stoves makes me want to play with fire more and build another one... We want to build a sauna/summer kitchen, and I really want to make a rocket cooker with an oven that also heats water in its spare time... Tall order.. I keep drawing designs up. I also want to do more experimenting with radiant floor heating.. Got the bug. ;)

Magic word, sauna, mentioned! :D

My grandparent's summerhome had a sauna stove similar in idea to this one, just 40+ years older:
http://translate.google.fi/translate?sl=auto&tl=en&js=n&prev=_t&hl=fi&ie=UTF-8&layout=2&eotf=1&u=http%3A%2F%2Fwww.puuilo.fi%2Fcat%2Fproduct_details.php%3Fp%3D97   (sorry for google translation)

20 litres of hot water usable every time you heat the sauna. Makes bathing much more enjoyable, if the only alternative is cold-ish lake water... :D

Unfortunately that summerhome was sold few years ago, so I can't really go there and take pictures anymore. This is indirectly related to the topic, since I would have loved to share pictures of the house's fireplace (and house altogether, it was hand built by my grandfather in the 70's).

The difference I often see between finnish and american fireplace design is that here fireplace is usually built in the middle of the house (and it's massive, to store heat) while the american counterpart is often built on the outer wall or it's a small metal box in the room. Something that caughts my eye often :)

paul wheaton

I did a kickstarter last spring.  It was successful, so now I am selling the DVDs of the rocket mass heater workshop with Ernie and Erica:

http://www.richsoil.com/rmh-dvd.html

And I've started a new kickstarter for permaculture playing cards:

http://www.kickstarter.com/projects/paulwheaton/permaculture-playing-cards



Erin

It's really funny that you updated this yesterday, paul!   [cool]

Last night, my son was playing with the burn barrel, with a smaller one stacked in/on it (he backed the pickup into it this spring so there's a dent big enough to leave an airspace below the smaller barrel when it sits on the caved in part), and a stovepipe.  He discovered that by making this tall thing with an airspace below that he got a MUCH better burn.  The ash is almost gone. 
Then he sat down and sketched out a "real" stove complete with "bolted connections and welds and everything, Mom."  My son is 13.

But looking at his rough idea, it occurred to me that that's basically a rocket stove... So today he's researching (if he ever decides to drag himself out of bed lol)
The wise woman builds her own house... Proverbs 14:1

paul wheaton

I just started another rocket mass heater kickstarter.

The last one from a few years ago was just a video of a workshop and we sold way more than I thought we would. So now we are making an effort to make something much more professional. These videos would be in addition to the videos from before - not a replacement.

https://www.youtube.com/watch?v=49khDHMqyUw

https://www.kickstarter.com/projects/paulwheaton/rocket-mass-heaters-4-dvd-set