Sub-Floor RMH for Wofati Eah

http://earthaboveheaven.wordpress.com/

Building a rocket mass heater into the floor of a wofati, (this one) for the first winter at Eah, a permie-micro-farm-within-a-farm-project here at Bardo Farm.

from Eah blog wrote:This is just a mortar-free dry-stack mockup of an 8 inch system. It uses fifty-nine firebrick splits for the heat riser, feed tube, and the sides and ceiling of the burn tunnel. It also uses eight 7″ square concrete pavers for the floor. The interior dimensions of the burn tunnel are 5 3/4″ tall by 8 1/8″ inch wide, and the heat riser is 7″ square. Two of the firebricks need to be trimmed a bit for everything to fit more smoothly, so this iteration was slightly off at the feed tube and the bottom of the heat riser.

Once lit, it drew nicely, roared/purred a little, and produced very little smoke, just a bit at the beginning and at the end of the burn. Note that the vertical heat riser is around twice as long as the horizontal burn tunnel. Relatively taller heat riser corresponds to a greater convective draw. It could be taller still to be at a reasonable height for cooking on, which should also improve draw. The next component to test will be the additional insulation around the heat riser, which should improve draw and efficiency of combustion.

Currently considering a few different options for containing the insulation (perlite) around the heat riser. Could go with a couple 30 or 35 gal barrels welded together maybe, (have one so far,) or there's an old water heater around here that might work with some cutting, or maybe trying to attach together two or more sections of 8" or 6" snap-together thin steel pipe, (the ones I have are taller versions of this thing from home depot, and I'm not sure how circular I can actually get multiple-snapped-together to stay.)

I have the two outer barrels, 55 gal steel drums, a little rust but no holes. Still need to cut one once I have a final height, and then weld? them together. Unless I go with something other than barrels?

Sharing my progress and thoughts here so y'all lovely permies can feed me some back.

Two comments;

first, have you insulated underneath the burn tunnel?

Then for containing insulation, thin sheet metal rolled by hand and riveted is perfectly fine. Or even held by wire!

Have no plans yet to insulate under the burn tunnel. I think I'm okay with storing some of the heat produced there. Once the floor gets heated up a bit it draws fine, but I suppose it would draw better sooner if it was more insulated. It's just dirt underneath the bricks so there's no fire hazard. I realize the more insulated you can get the burn tunnel and the heat riser, the better, but supporting the burn tunnel and the rest of the core above an air/perlite gap would mean I'd need more bricks or something, I guess, it might be worth it. Or did you mean using sheet metal to contain the insulation around the burn tunnel as well, not just the heat riser? Or some other insulation material?

Mate, insulating the burn tunnel makes for a cleaner burn, and better efficiency, plus less ashes.

I don't lnow what's availlable to you.

But for under burn tunnel, i like stuff like cellular or air entrained concrete like Ytong

http://www.archiexpo.com/prod/xella-ytong/cellular-concrete-blocks-thermal-stone-insulated-weight-bearing-exterior-walls-55245-126529.html

Or mineral wool (rockwool) panels. Actualy i checked, the closest to what i use is, i think, Roxul Rockboard. if put under compression, it doesn't matter if the glue fails at 900C° or so. In other spots, you need to contain it. Like with sheet metal. I have encased rockets in gas bottles etc! There's plenty of ways. I only have explored a thousandth!

Regarding metal in RMHs. Am I right that you can use metal before or after the riser but not as the riser? And I noticed some people are using metal to form the inside and outside of the riser so does the inside metal tube melt or disintegrate with use if it is not removed before firing?

Wyatt Barnes wrote:Regarding metal in RMHs. Am I right that you can use metal before or after the riser but not as the riser? And I noticed some people are using metal to form the inside and outside of the riser so does the inside metal tube melt or disintegrate with use if it is not removed before firing?

Not in the heat riser, nor in the feed tube or the burn tunnel. Elswhere, you only have to deal with rusting and expansion. There's no spalling elsewhere, but in the burn unit.

Wyatt Barnes wrote:Regarding metal in RMHs. Am I right that you can use metal before or after the riser but not as the riser? And I noticed some people are using metal to form the inside and outside of the riser so does the inside metal tube melt or disintegrate with use if it is not removed before firing?

Here is my 2 cents :

Have a look at my thread

https://permies.com/t/40107/rocket-stoves/hot

I wanted this thing too get supper hot, and the only way too do that is too insulate around the burn tunnel. . . I used 6 inches of clay and perelite all the way around but the top . . kinda tight for room on top . . . I just used one of my bricks on the flat part and tamped it lightly into place.

Next thing is yes, the riser is made out of 2 pieces of duct working - and yes, the inside one is almost all gone - flaked off down into the burn tunnel and cleaned out . . but, since the riser was insulated with the same clay perelite mixture, it is still solid - hard - dried clay/perelite.

I am also planning on building an unconventional house, and would like to build a rocket mass heater into the the floor. . . I am thinking along the lines of a 4 x 4 foot pit - Insulated on all sides with 12 inches of styrofoam to send the heat up - not into the ground - build the core of the rocket as I already have with this one (10 inch - not 6 ) and have the whole unit sitting on a "wall" say about 2 or 3 feet high (high enough for the burn chamber to be level with the floor slab) and just wide enough to be able to put in the 10 inch exhaust with 1 row of bricks on each side filled in with cob so it is a solid square - 35 feet long - single run exhaust pipe. Then come in with the concrete truck, and just fill in the trench with concrete.
That way, the exhaust pipe will already be encased in dry - hardened clay / brick and I won't have to worry about it collapsing or bending with the weight of the concrete - I can also test fire the whole unit before the concrete even arrives - any problems - just fix it ! Then pour.
After the floor slab goes in with the radiant floor tubing installed, the heat from the stove mass - should - radiate up thru, and with the circ pump running, should heat the entire slab. . .

You will notice there is alot of "shoulds" in there . . . not alot of people have responded to my thread as of yet . . .

https://permies.com/t/40109/natural-building/cut-cover-house-lighting