Vulcan parlor stove - can I convert it to an RMH?

I was wondering if anyone has modified a parlor stove to a rocket mass heater?  I am attaching a Vulcan gas parlor stove that I would like to modified.  I am planning to make some changes to the stove and build a clay rocket stove and hook it to the parlor stove.  Anyone has any suggestions?  thank you

Howdy Ken, welcome to permies!
Could you tell us a little more about how exactly you are going to set up the system.
Others here have a lot more experience than I but from what I have read here you might have trouble with the metal if it is used in the hottest part of the rocket stove.

Looks like old english coal stoves, with an open fire?

More pics would be in order.  Tho, i wouldn't hold my breath, i can't see that much can be done with it.

more like a French Godin cylindrical type I would have thought

If it does not have a narrow neck partway up, you might be able to cut out the bottom of your stove and use it as the "barrel" surrounding your insulated heat riser. This would require the system size to be small enough to fit the riser diameter plus insulation on each side with a couple of inches or more of free air space all around for the downflow exhaust.

So what are the internal dimensions of your stove, especially the narrowest part, and what kind of space do you want to heat with your system? You may not be able to make a system using this stove that is big enough to heat a house.

Its very nice looking ,I can see why you would want to keep & use it.  As stated it would probably be best used as a bell in the mass.  Could work over your riser but would be a 6" max system, and tolerances might be too tight.

Thanks everyone, I am thinking about using it as a bell.  I just ordered 50lbs of clay and I will be going to home depot later to get some sand.  I may have enough clay and sand to build a rocket mass heater with 2-3 bells without using the stove.  I will start without the stove to see how it goes.

Sounds good! Keep us posted on your progress, and don't hesitate to ask if you have any more questions.

So i decided to build a cob rocket mass heater with 2 bells and a little oven.  My dad and i spent the last 4 days mixin the clay and sand together and building the "castles" a little per day.  And we are almost done!  I do have a few concerns:

I don't really have a fire tunnel from the j tube, would that matter?  Would that stop the rocket effect?

I'm mixing the 5 clay to 4 sand but there's not fire bricks.  Would that not holding the heat as intended? I have read that fire bricks are clay plus sand so seems to me like i should be okay.

I don't want to test the fire until the cob is completely dry, which takes about a week.  Am i over react?

Good for you for trying stuff! I hope you can clarify your setup for us; I can't tell from the photos how the airflow is supposed to work, You say you don't have a "fire tunnel" (burn tunnel is the standard term)... I take it the wood feed is the about 4" diameter hole? What is the internal shape and size from there? It looks kind of like a square hollow much larger than the feed hole. That would not work at all for making a rocket combustion chamber. You need a vertical feed tube leading to a shortish horizontal burn tunnel, leading to a longer vertical heat riser. All of these need to be approximately the same cross section. The feed tube and burn tunnel are generally built square, while the heat riser can be square or round (round is more efficient by a bit).

I am assuming that you plan to close off the tops of the chambers with slabs that we don't see.

What kind of clay did you use? If it was ceramic or pottery clay, I am concerned that it may not stand the fast temperature rises you get in a rocket combustion chamber. Even if it is bone dry, there is still water bound up in clay, and if heated too fast it will flash to steam and explode, destroying the clay.

You need insulation around the combustion chamber, like perlite, so it doesn't lose heat too fast and burn cool and smoky. This is especially important for a 4" system size, which is at the small end of what is possible to function, and is often difficult to get right. Larger sizes are more forgiving and easier to get right the first time.

Thanks for the quick replay.  The feeding box is in fact hollow, Can you please tell me more about how to build the feeding box and the burn tunnel?  

You're right the top will be closed.  

I have the feeding box going directly to the secondary burn chamber, which doesn't have a burn tunnel.  The burn chamber release hot gas to the first bell on the top 3 holes.  The first bell release hot air on the bottom to the second bell.  I'm hoping that catch all the hot air with the bells.

I got the clay from Amazon.  I think it's pottery clay.  I used 50lbs clay and about 30lbs sand.

I'll wait a week to let it try before testing it.  

Thank you

Hi Glenn,

This is the clay that i ordered and i also attached a picture of the fire box for your review.

https://www.amazon.com/Amaco-45047J-High-Fire-Moist-Stoneware/dp/B0044S97BW/ref=sr_1_4?s=industrial&ie=UTF8&qid=1482544041&sr=1-4&keywords=50+lbs+clay

The path through the bells sounds fine, but the combustion is definitely not going to work the way you are hoping. If the clay at the feed is still damp enough to carve, I would suggest making the hole a couple of inches wider to give yourself some working room. Do you have any clay left over? Can you get perlite? I would advise taking some clay (sanded or not) and mixing it evenly with three or four times as much perlite by volume. This will make an insulative mix that can be formed into tubes or slabs. The perlite will create enough airspaces for water to escape from the clay without exploding.

I am going to describe a process assuming that your box with the feed hole is 8" high; adjust the proportions according to what it actually is.

Make a box 4" square by 12" long inside, with a 4" long lid for the middle third (kind of like a small shoebox). Set this in the hollow, with the center lid beneath the wall dividing the feed hole from the riser area.

Make a 4" square by 4" long open tube and set it on one end of the burn tunnel box, about where the feed hole is now. Carve out the feed hole as needed to fit the new tube. The top of the new feed tube should come to the top of your current feed surface more or less.

Make an approximately 4 1/2" diameter tube of perlite-clay, forming around something if you have it, as long as you can make it to sit on top of the other end of the burn tunnel and have a couple of inches of clearance below the top slab. Let this dry enough to stiffen up, then set it in place on top of the burn tunnel and seal the joint with a bit of clay. Add a few clay braces if you want to, to keep this heat riser tube from shifting inside the bigger square box.

Pour perlite into the hollows around the feed tube, burn tunnel and heat riser, at least halfway up the riser or more if you can.

This will make a well-insulated combustion chamber that will probably burn cleanly, and give you a good amount of heat for your bells.

Hi Glenn,

Thank you for the detailed fire tunnel.  Unfortunately the fire box is very dry.  I think i still have 5 lbs of clay and 20 lbs of sand.  I can order perlite from Amazon.  We will be finishing the heater tonight.  

Do you think it's possible to fill the fire box with left over sand to replace perlite?

Sand is too insulative to be a very good thermal mass, but it is too dense and conductive to be a good insulator. I would probably leave dead air space before using sand as an insulator in this case.

The problem is that you need the perlite for the internal combustion parts, or the clay will not be able to release its bound water fast enough and will probably crack or explode when you first put fire in it, no matter how dry it feels. I strongly advise you to wait until you get the perlite to finish the combustion core.

One other thing - what kind of floor do you have beneath this construction? You need some air space between the clay bells and the floor just to avoid heat getting sucked out where it does no good, but more importantly you want to make sure that any wood subfloor does not get hot, as eventually it may start to char even if it is not getting to full combustion temperature. If you had a larger system, I would also be concerned about a concrete subfloor overheating under the burn tunnel and spalling, but that is not likely to be an issue with a system as small as yours.