rocket mass heater

[Don_P]

I'm hunting for barrel 6 for a reason

[Ernest T. Bass]

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..

[glenn kangiser]

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.

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.

[paul wheaton]

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?

[Ernest T. Bass]

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.

[Freeholdfarm]

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.)

[paul wheaton]

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

[Tifflery]

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!

[paul wheaton]

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.

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.

[JRR]

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".

[chris802]

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?

[Don_P]

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.

[NM_Shooter]

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.   

[MountainDon]

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.

[Don_P]

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.

[chris802]

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:

[Don_P]

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.

[Ernest T. Bass]

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.

[paul wheaton]

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.

[Squirl]

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.

[paul wheaton]

Why not just install a fresh air intake? 

I have one on my rocket mass heater.

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