Rocket stove-no cob

has any one done a wood or brick outer cover - permanent placement
would put it on a outer wall
would need mass for 8-12 hours of heat
would take place of woodstove which takes 4-6 cords/yr
would cover barrel with brick lattuce- could use brick/wood covering else where

has any one put water pipe or pex  to take heat to a tempering tank for on-demand water heater and maybe some how send hot-water back to stove to take the place of a big radiator when no one is home
Bill in northern Wi

bill1111 wrote:
has any one done a wood or brick outer cover - permanent placement
would put it on a outer wall
would need mass for 8-12 hours of heat
would take place of woodstove which takes 4-6 cords/yr
would cover barrel with brick lattuce- could use brick/wood covering else where

Here are some all brick ones:

http://mha-net.org/docs/v8n2/wildac09f.htm

http://mha-net.org/docs/v8n2/wildac10h.htm

I have seen others on the web, but don't remember where...

Also check out:
http://flashweb.com/blog/2007/11/bed-and-bath-doorway-arches.html
or
http://www.handprintpress.com/ovens/bring-in-the-mud/
Where they use an Iron stove, but surrounds it with mass.

If you want to stay completely away from cob, but still use an iron core... this idea might work well:
http://www.iwilltry.org/b/build-a-rocket-stove-for-home-heating/

Use it as the core and put your bricks where ever. The good thing about it is that the flue path is all sealed metal and the bricks don't have to be air tight. The barrel could be made with a flat top so cooking on it is possible. Those who are in the know say his tiny 3 inch riser and 4inch flue path is too small to rocket right... he didn't try to heat mass with it so it worked ok for him. You should use at least 6inch.

If you go all out brick, it may be cheaper to use it to make a masonry heater instead. They can be made with pretty much all you want in them and can be built "to code".

The hardest part to do without cob is the barrel to base to bench interface.

in place of cob you could build a form and pour a refractory block to seal the barrel and pipes ,ect.
in a MH the wt is in one place - was thinking I could spread it out somewhat with a RMH 
it would be nice to build a fire at 2200 and have the house 60 degees at 0600
now I have a large fire going when I go to bed - it is shut way down - not the best way to burn wood
have heated with for 35 yrs - vermont castings , jotul ,fisher , and even a barrel stove.
would like to cut a lot less wood - i use maple and red oak - put up aprox 4 cords/yr
I use trees the road crews cut - our township lets us take it- some trees on our land and buy some in 100 inch sticks
has anyone added a small bump out with a outside access for the fire box with the barrel inside the home
has anyone tried a bigger wood feed to use 3in rounds
Bill

bill1111 wrote:
in place of cob you could build a form and pour a refractory block to seal the barrel and pipes ,ect.

That would work. You would be looking for a flat surface and use a gasket.

in a MH the wt is in one place - was thinking I could spread it out somewhat with a RMH 

I have seen masonry heaters (MH) with quite long benches too. The small footprint of most MHs has more to do with tradition than anything else. The peasants houses were small already, how much space did they want to take up with the heater? In some ways this still drives heater size today. The difference between the RMH and the MH is the burn type. The MH is a batch burn. The whole of the fuel for one burn is put in the fire box and lit. when it burns down it is maybe stirred, but fuel is not added. Maybe two hours of burn. Then the mass is expected to do the work for 12 to 24 hours. With the RMH, there is a continuous feed by the operator over three to five hours because the burn chamber is much smaller. So you would have to start your burn 3 to 5 hours before bed. Once the burn is finished the mass works for 12 to 24 hours as in the MH. There are people with both a MH or a RMH who say longer than 24 hours, but that is normally in "shoulder seasons".

has anyone added a small bump out with a outside access for the fire box with the barrel inside the home
has anyone tried a bigger wood feed to use 3in rounds

Even a 6inch RMH should handle 3 to 5 inch rounds.

seems like the barrel puts out a lot of heat which could go into the mass
have been in houses where it is 100 degrees
is there someway to tweak the design to change the amt of to the mass?
I like the looks of the bell design

2 or 3 5in rounds must last for a while

no woodstove is a set it and forget

more money to build a MH
what about putting tubing from a tempering tank in the mass
Bill

bill1111 wrote:
seems like the barrel puts out a lot of heat which could go into the mass
have been in houses where it is 100 degrees
is there someway to tweak the design to change the amt of to the mass?

I don't really know. The theory is that the top of the barrel needs to be hotter than the  bottom for it to work right. Brick sinks heat faster than air does, so the bottom and sides should have no problem with brick/cob/refractory concrete as mass. Even the top could probably do ok with mass close to it if that mass was isolated from the mass at the bottom... or if there was air space between the barrel top and the mass... maybe like a white oven?

I like the looks of the bell design

I want to try making the flue through the mass/bench/bed bell like. An oven over top of the barrel would act like a bell too.

2 or 3 5in rounds must last for a while

From the video I have seen, the wood they use is pretty short... maybe 6 inch long instead of 18inch. I think this is to guard against the wood burning up out of the feed hole and it's air flow and smoking the house out. I have some ideas I would like to try to get around that. Also remember that the idea of the mass heaters is to burn that wood as fast/hot/clean as you can.

no woodstove is a set it and forget

I meant to say that in my last post  That is the upside of a mass heater, you don't need it to burn all night, burn while awake and the heat should last all night.

more money to build a MH

once you start using the same materials in a RMH as a MH... the costs start getting about the same real quick. If you have to start adding engineering costs to the RMH then it could cost even more. There is really not that much difference between the two. Just a different burn chamber/style. The use of cob made onsite from onsite materials was the big savings in cost for the RMH. I have seen MH with a refractory core and stucco/used brick/compressed earth etc. for the facing to reduce costs too. The old Russian ovens where just as often made from local clay too. There are MHs that use a premade iron firebox with mass added around it after the fact. They even look like a regular MH.

what about putting tubing from a tempering tank in the mass
Bill

Definitely been done with the MH which means it should be doable with the RMH too. Lots of wood fired water heaters have blown up too. I personally would stay away from a pressurised water heater.... but then I know I don't know what I'm doing at least not with pressure plumbing. If you knew you were dealing with a part of the flue gas where the flue temp is always less than boiling it would be safer, but the water would not heat up real quick either. The ones I have seen in a MH the tube is either right in the fire box or in the top of a bell.

When testing MHs, they over fire them 3times. That is, they stuff the fire box full, burn it all and refill without cooling a few times. The out side temp of the mass is measured (often as hot as an iron stove gets) and then they tear it down and see what damage they find inside.... There has been some problems with Americans (as a generic term for north americans... us Canadians are not excepted) who are used to fireplaces who keep adding wood "'cause thats we the way we always done it, worked for me pappy and granpappy.... oughta work fer me too".... kind of mentality. Even though the masons teach the new owner how to run it and supply an operators manual....

Let me get back to a rocket mass heater - in my basement / walkout
i wuold like to build a large box filled with sand , the rest would be the same
opps i would like to cast the or build with firebricks then cast around them with refractory material
no cob
sand for mass on a concrete floor insulated from the heat
I would put a metal grate above it to deliver heat upstairs
it would be on a outside wall
I would like to use larger wood
or somehow use a bigger fire box
don't mind the feed on the utube but don't want to feed wood into it every 10 min
if i could add a oven on it that would be great
Bill

Sand isn't a great material to use. Sand acts like an insulator because of all the space between the grains of sand. Ernie says think of walking on sandy beach on a hot sunny day - the sand is hot on your feet, but is cool a few inches down. (The solar heat isn't conducted down very far into the sand.)

You might get away with using sand if you add metal or something to conduct the heat faster... maybe recycled copper wire wound around from the heat areas outward.

bill1111 wrote:
Let me get back to a rocket mass heater - in my basement / walkout
i wuold like to build a large box filled with sand , the rest would be the same
opps i would like to cast the or build with firebricks then cast around them with refractory material
no cob

The RMH is relatively new and each one is an experiment. The general steps are to build the core outside of the house and test out any new ideas you want to add... generally without the mass installed. In your case with sand (paul found gravel was better) I would try that outside too as it is different. This would allow you to see for yourself how fast the wood burns and how long you can leave it burn without adding more wood. I would suggest the 8 inch version as a first try as you would be able to fit more wood in the feed. Really 6 and 8 inch are the two sizes that have had much work done on them. If you were to try 10 inch or bigger you may have to build your own barrel to get it big enough to keep your cross sectional areas right.... in any case 8 inch flue (chimney) is pretty common.

Cob vs. fire brick... cob = clay+sand.... firebrick = clay+sand the sand is different in the fire brick as it is chosen to expand at the same rate as the clay with heat. Silicon based sand does not. Refractory mortar is also clay based. Refractory concrete... is a different animal(s). I know people have done cast in place and so it should work fine.

Are you still going to use a metal barrel? metal ducting? Can you post a sketch of what your idea is? The oven part... how hot do you want to get it? While anything over 180F will cook food.... if you cook it long enough (see the solar cooker pages), it does take a lot longer. It is not unusual to take 4 hours to bake bread. The reason I mention it is that by the time the gas gets to the bottom of the barrel it has cooled significantly. A hot oven would have to be above the barrel.... also the best place to use as a cook top. How much room does your oven need inside? Are you thinking of a white or a black oven.... hint a black oven won't work as part of a RMH. (I could be wrong... but the door would have to have a very tight seal and of course you couldn't bake during a firing but right after.)

Anyway, some more things to think about.

okay forget the sand and use rock 2 to 3 in in size
we don't have much clay around here - we are in sand country - north central Wi
I am in the brain storming mode about this
am in the middle of a remodel on the cottage so now is the time
would use the metal ducting to run heat thru the mass
can use the barrel and heatriser pipe
I could form up the the burn tunnel/woodfeed and place the heatriser in place and pour around it
add the barrel and brick around it - enclosing the barrel would allow for ducting heat upstrairs
could use outside air somehow
thats are far as I have got

bill1111 wrote:
okay forget the sand and use rock 2 to 3 in in size
we don't have much clay around here - we are in sand country - north central Wi
I am in the brain storming mode about this
am in the middle of a remodel on the cottage so now is the time
would use the metal ducting to run heat thru the mass
can use the barrel and heatriser pipe
I could form up the the burn tunnel/woodfeed and place the heatriser in place and pour around it
add the barrel and brick around it - enclosing the barrel would allow for ducting heat upstrairs
could use outside air somehow
thats are far as I have got

Sounds reasonable. I'm assuming the feed/riser are refractory concrete. This means that by the time you get to the facing it should be cool enough to use concrete patio block like this:

(I don't think your's would look anything like that one being a RMH, but the same technique could be used for the sides of your bench if cob not available)
They have laid it shiner, but you could do flat too (for more strength to hold in the weight of the gravel... or thin (I think it comes in 4in.) reinforced cinder block if you need to). They have used refractory mortar, but portland should work too. You could cap it with 24x24 (or 36 by 36) pavers. Remember if the pavers aren't wide enough to bridge the whole thing, the join needs to be supported so the ducts don't get crushed. Paul used wood on his:
https://permies.com/permaculture-forums/2558_0/alternative-energy/portable-rocket-mass-heater But so far has not added any top to his (probably to keep it's portability). If you didn't want the brick look, it can be covered in stucco. the big thing you loose by not using cob is the low cost. All of these things cost more than cob, but if the cob has to be imported that changes things.

Outside air: You must have makeup air of course. If it is better to run dedicated ducting just for the heater or not I don't really know. Personally, I would like at least some of that air to come from my house interior. that way it helps vent my house. So at the very least I would bring any ducted combustion air close to the feed but not right in the feed so that the air pressure in the feed is negative compared to the house to prevent CO build up or smokeback. As with any wood burner, a CO alarm should be installed.

For those who are interested..... here is a RMH made of masonry. No steel, no cob.
http://mha-net.org/docs/v8n2/wildac11h.htm

It was built quick as a demo and then knocked down at the end of the week and so the bench is rather small. It also goes up a chimney and so the exit temp must warmer to make that happen.

Is there any plans for the one show at the MHA website?

jtcweb wrote:
Is there any plans for the one show at the MHA website?

As it was an off the cuff, spur of the moment thing, I don't think so. However, the feed, the burn tunnel and the riser are fire brick.... everything else is standard clay brick.

Firebrick = 9x4.5x2.25
clay = 7x3x2.5
pavers for base look 12x12
Aprox. measure your own for something more accurate

The mortar is refractory.... clay based. (they use it because it expands at the same rate as the bricks..... and, in this case, because it is easy to tear down at the end of the week)
The firebrick will be laid with about a 1mm gap (maybe less, think as close as possible) and the clays are normal so that the corners work out (3/8 inch?).

Count the courses of brick and the number around the perimeters. Remember the CSA should remain constant... or at least the riser should be the smallest CSA (I suspect the bench cavity may have a relaxed CSA.... looks like 2 or 3 times bigger). So the burn tunnel would be 7inches across and 6.75inches high...for example. The "barrel" seems to be 5x4 clays (plus gap). The riser is fire brick laid shiner with ends flush on the outside... so the inside would be 9-2.25=6.75inch square...and 9 courses high (9x4.5 inch). It is capped with oversized fire brick? premade refractory concrete slabs? Soap stone slabs? ... one or t'other.

Note there are two openings on the bottom of the "barrel" into the two benches. These benches are short by RMH standards.... for two reasons.... this is a demo, and because it feeds a chimney. I do not know how long it could be made and still work well. Ask Max

Best to build it first in the back yard.... My impression is that while this is great as a demo, the form factor would be hard to fit into a house. The flue is right in front of a major part of the bench for one....