The burnstack is firebrick, wrapped in 1 inch unitherm ceramic insulation. The unitherm insulation is held in place by a couple of strands of wire, then I wrapped with metal mesh that is used for stucco. I think this is good to go, but need to decide if I need to clad the stack in fireclay. The fireclay mix would adhere nicely to the metal mesh and might protect the metal mesh, but I am not sure if this step is necessary.
another look at the burn stack, this time looking down at top before I wrapped with the metal mesh.
Cleanout at the beginning of the run back toward the burn chamber. The fan idea is gone.
Wrapping with left over unitherm, then moving back to build up with fireclay and cob mix.
You can see the ductwork/riser to left and behind the burnstack. It will come out of the cob with a heavy 8 inch single wall stove pipe, then reduce down to 7 inch black stove pipe and runs about 5 feet back and slightly up before it does a 90 degree turn and into the brick chimney flue.
THIS IS AN OLD POST. WE MOVED THE UNIT TO A DIFFERENT INTERIOR WALL SO THAT WE COULD ACCESS THE EXISTING BRICK CHIMNEY. STILL USING THE SAME BRICKS BUT NO FOAM BOARD UNDER OR AROUND THE UNIT.
Got our bricks.
Thank you to Shawn and Amanda for taking a drive to Eugene to pick these up
These are not the dense heavy firebricks that I was expecting, but the lighter insulating firebrick. These are supposed to be easy to cut with chisel or hacksaw. I am going to need to do a little research and make sure the characteristics of these bricks are suitable for the rocket stove. It seems like they should work, they will allow the heat to build inside the chamber and they should not absorb much of that heat. I think that works because I want the heat to travel through the j-tube, build to high temperature in the riser/barrel and then I want the heat to transfer to the thermal mass before the exhaust exits the building.
I started laying out the bricks and thinking about brick count, how to construct the J tube, the heat riser, the support for the barrel and the ash cleanout. Here are some pictures:
I don’t think that’s going to work. The weight is going to deform the foam board. All of the foam board ideas are gone.
I was mainly just laying out the burn chambers and stacking brick to see how the rocket stove will fit in the space. I really wanted to light up some paper and see if the rocket stove would draw as it is set up here, but I resisted the impulse. I don’t think we are ready for that step yet.
The picture above shows the heat riser extended up a bit so that the top of the heat riser would be about 2 inches below the top of the barrel. I also played around a bit creating an ash cleanout pit. That is the the rectangular space in the foreground of the picture above. The ducting would then come out of the ash cleanout cavity, run forward toward the position of the photographer in this picture (thanks for camera work, Marylea) then it will turn 180, run back and end in a stack that will rise and go out the “window” space just above the rocket stove. I am going with the stack up and out of the mass heater in close proximity to the heat riser as Ernie and Erica have suggested.
Here is a picture of the rocket stove with the barrel lifted and in place over the heat riser. (pretty barrel, right? need to spray that down with some bbq high temperature paint)
I think I will have to bring the whole rocket stove forward at least a foot so that I can get 2 feet of clearance between the barrel (that is going to get very hot) and the frame wall behind the stove and the ceiling above the barrel.
I think I will end up with a fireproof material on the walls near the barrel and on the ceiling above the barrel. I am thinking about durock board, then maybe I end up with tile on wall behind or maybe just a cob type plaster.
Question for today:
- Am I going to need to “glue” the bricks together with a firebrick mortar or cement or will I be able to mix a cement/cob material with vermiculite and seal the burn chamber, the j tube, the heat riser and the ash cleanout?
Going slow. Having fun laying out this project. We have been thinking about this for a long time.
It will be a few days before I can get back to this project. I get my first day of jury duty tomorrow and also need to get back to the office grind for a reasonable number of hours. Words need processing, phones need answering.
We want to keep as much heat from the mass heater in the house as possible. One of the ideas with the rocket stove is that we will be able to dispose of trash wood, prunings, etc more easily than we can now, but another idea is that we want to extract the heat from the wood and let it help heat the house. This place is amazingly easy to heat with gas-fired radiators throughout, but what’s the harm in improving and adding options for heat?
So, the concrete slab and foundation are almost certainly not insulated from ground. The basement is about 3 feet below grade. So even though heat rises I am trying to design and build mass heater that radiates most heat up and out into the basement space and then up through the house from there. I am trying to avoid losing heat through concrete walls or floors into the ground. So, we picked up some polyiso foam board off craigslist. Some of it is a little rough, but I think it will still work fine. The foam board is 2 inch. Here is where the design question start to arise:
- Should we place the foam board right on the concrete or float it above the floor with 2 inch space between concrete and foam board?
Looking out on the internet is not real helpful. There are not a lot of people using foam board on top of concrete in a rocket mass heater project. The consensus view appears to be that there is no problem with putting the foam board right on the concrete. I think that makes sense because this same kind of faced foam board in put under concrete slabs, so it must be pretty moisture-tolerant.
Here I am just laying out the foam board and starting to think about the footprint of the rocket mass heater. I am going to follow a standard Ernie and Erica layout – rocket stove in the corner, barrel/manifold right behind that, stove pipe and mass heater to the left, then back to the corner and up and out behind the barrel and out through the glass block “window.”
Ernie and Erica think that the heat from barrel radiating to the cooler exhaust pipe helps the heater draw well and I think they are right about that.
I am contacting Ernie and Erica to see if they want to function as consultants on this project.
Found a good deal on fire bricks in Eugene, so our daughter is down visiting friends, family and picking up bricks for us. Bricks are supposed to arrive tomorrow, Sunday, March 8, 2015.
Questions that I am considering:
- should I put air spaces under and around the mass heater so that the heat can scoot under from down in front and then rise up and out from the space between the frame walls and the masonry mass?
I think yes on this question. I don’t see a downside to attempting to create a radiator-like air pattern around the stove. I think we may get more air movement with this plan and not have to rely quite as much on the radiant heat from the masonry mass. I am doing some checking on that. Here is an example of that kind of approach from Ernie and Erica.
Ernie and Erica are my “go to” experts on rocket stoves.
- Will the foam board be crushed or damaged by the weight of the firebrick, the manifold, the mass heater?
- How much heat protection am I going to need between the rocket stove, the barrel manifold and the framing?
- Can I build a plywood floor above the foam board, then put the stove pipes in on top of the plywood? How much cob, gravel, or rubble fill will I need on top of the plywood or foam so that the material under the mass heater does not get over-heated.
More soon on this project.
Ok, time to build the rocket stove mass heater. We have been thinking about it long enough. These things look amazing and they don’t look like they are too hard to build, but we will find out about that.
Here is the setup:
Took out the two windows. Sills were rotting out. Reframed those for replacement with glass blocks that we picked up last year. We are on a glass block kick. Old windows were single pane, 100 yrs plus old. Most of the windows on the house are still original with storm windows added in the 70s or 80s. We framed up a wall behind the washer and dryer. Pressure treated 2×4 on the concrete, the rest just 2 and better doug fir. Lovely wood to work with. Strong and forgiving. We plan to sheetrock over the 2x wall. The wall cavity is about 7 inches deep, going to fill that with blow in insulation, so this should be a decent upgrade in the thermal characteristics of that wall.
cleaning up the wall a little bit. It’s an interior wall, load bearing, storage room on the other side.
Living in close proximity to friends and family is a wonderful thing. What if you could design and build a complete community with a very small footprint? Would you do it? What are the challenges and the payoffs?