Wondering who else has buried a rocket mass heater chimney made of sched. 40 steel in a large house concrete floor and thermosiphoned hot water from the firebox loop into a storage tank to pump down into pex zones buried in the concrete floor away from the chimney? This works well in our two houses.
I watched my uncles when I was a kid harvesting and shocking oats with scythes finishing up a field on our farm-- the horse drawn sickle bar broke a tooth. I grew up using the scythe as commanded on weeds around outbuildings and machinery. I obeyed, and competed with cousins swinging those things. Now at 74 and farming again after almost 50 years teaching, I enjoy showing a 16 year old how the scythe works better than weed whackers to mow irrigation lateral ditches so the water can flow. It doesn't leave residue in the ditch to pile up and block the cuts. And it doesn't leave a stench in the air, that gift from God very worthy of being protected by us humans... So much to be gained back starting with those simpler technologies that turn out to be superior to those requiring so much more complex tech, energy investment, and fossil fuel emissions. I'd rather breathe longer.
"Do you have photos of your setup? Where did you put the RMH firebox loop, to pull the most heat from it, without affecting the RMH's operation (and risking a steam rupture)? I understand that the loops are open to the air in the tanks, so I gather that if the water is kept circulating, you don't have to worry about steam forming in the piping in the actual RMH?"
Loops are closed to the tanks; I try to keep the airhead in the tanks as small as convenient. There is no valve on the overflow; it's open to a drain. I could/should have designed it with a waterseal "U" to virtually eliminate recharging the airhead with O2, I eliminated check valves, so water can now circulate either way (and does so mysteriously) through the RMH loop. The third loop I didn't mention is driven by a pex pump to bring water from the top of the tank (where temp is highest) into the floor via three pex zones. The pex pump is driven via a simple 110v house Tstat that only has power when a stack Tcouple switch on my RMH on at 120F closes. there is no pump to drive the RMH loop. It works fine that way except when a leak in the outside solar loop from too much heat on the hose connections drains the tank so low that the firbox loop starts reversing like a swing and banging from little steam explosions (remember the old hotel steam heaters?)
Some photos are in our website www.greenwoodfarmmt.org. My firebox loop is S steel 3/4" sched 80 pipe custom welded for high pressure, with my design having six weld elbos, it cost over $200. It's not a BAD investment considering the possibility of failing check valves or obstructions, since a steam explosion is possible given the high temps in RMH firebox. That's my first installation. My third installation is still open to question. I'm working on a barrell lid for my 3rd RMH that will place a 1/2 copper coil just under the lid so the coil contacts the vent flow from the RMH. I hope these gases are not as hot as those in the firebox itself. Should I put a cap of 3/16 steel with a 1 1/2" gap above the top of my burner pipe? That would protect the copper from direct vent flow at this secondary burning location? Not sure it's necessary. But with copper, I need to make sure water is ALWAYS inside those coils.
Laura and R Scott: My first tank is a 300 gal steel propane tank discarded (and the gas roasted/burned out on a huge bonfire) it's still in use. It's really heavy, and needs a barrier to the air. My 2nd and 3rd tank systems are simple black poly. The hot water from my RMH firebox loop, and the water from my solar collector loop, are almost never above 140F when they arrive at the tank. These storage tanks are not sealed for pressure, they have none except gravity. When the tank approaches 90, a pex pump comes on to heat the floor with that contaminated water. The loops inside are pressurized, with uncontaminated potable water inside to draw out the heat to go to the inline heaters. With pex pipe coils and garden hose collectors, maintenance is not expensive. I have not yet shut the valves to replace any rubber hoses, might about every 5 years if I keep water flowing or shade them in hot weather so I don't let them boil.
Why not isolate the legionaire or any contaminant possibility from potable water? I put the potable water under pressure inside a coil of 3/4 pex immersed in the preheating tank, no connections inside, The water on the outside of the coils, in the tank, has no pressure, and this circulating water is sealed from air, and passes repeatedly through the collector (I use black rubber hose coiled over highly selective solar aluminum) under a double glazed surface. No freeze problem, and high temperature gain results. For the potable pressure water 3/4 pex coils work better than 1/2 because of resistance and pressure drop to the hot water faucet.
In line heaters have temperature fluctuations? So do all cows eat grass? No way; it depends. Some eat silage or alfalfa. I have have an instant-flow micro-adjusting water heater with no tank, built to make some 20 adjustments per second to maintain temperature when incoming water temperature or flow rate changes. Chronomite is one company that makes them. These ultra-small units install easily at point of use, and work well if a pre-heater tank varies in temperature. My tanks are easy to maintain around 80F with energy sources easy to control. I hope my systems last longer than my last investment in a 30 gal. tank hot water heater...
What are potential problems with a black hose solar collector? The obvious advantage is no freeze-up problems. Otherwise it seems cost-effective and reliable.
My first black hose collector was laid out on the lawn and connected via closed loop to my hot water storage tank inside the house 2nd floor. Thermal syphon did the work, and my storage tank stayed between 80 and 90F all summer, adequate to preheat my copper coil inside the tank for domestic hot water via my 30F rise in-line heater. Now I have two collectors in operation with a fountain pump (increases efficiency), glazing, insulation, and old aluminum siding with the raw side sanded to retain highly elective solar collector surface black paint. Now all my pipes are pex, the tank is cheap poly, and I use a fountain pump 120v controlled by a simple air conditioner T-stat placed in a window directly in the sun. The hose is coiled inside the collector, on top of the black aluminum, and under glazing.
Thanks for the feedback!
Well, chagrin. I'm dumping the gas idea. Our barn house totally is 40 X 60, made mostly of ICF's. My rocket stove has a firebox 6" wide and 8" deep, about 26" long. Over half the winter heat needs are met with passive solar. BUT after seeing that in both installations the firebox is the lowest point of the entire floor, even a very tiny propane leak would accumulate and risk a devastating fire and explosion.
Because of that, no propane. I will install a backup heating loop into the pex floor loops from a conventional 40 gal or better electric hot water heater. The primary source of heat for this floor loops will be the RMH. The new house will be 32 X 52, also with over half the winter heat needs met with passive solar. A similar installation is what I would put into our existing barnhouse, if a really bad winter comes up or my health doesn't hold up to cut firewood for my RMH. I burn LOTS more and don't like it when we go a week with no sun and the temp doesn't climb to thawing. It's much better to have 0 in the daytime and full sunshine.
Thank you Chris! I was misinformed about diatomaceous earth being a generic term for the bentonite material I hauled on my big trailer! What I got worked very well, and I have the brick to prove it, but as you so well point out, it's bentonite, and a VVEEERRRY sticky clay. Not diatomaceous earth. Thanks.
Bentonite, here in MT, is the brand name for the type of diatomaceous earth used for sealing oil well casings, around the perimeter of basements, and incidentally in health and gardening. The two mines in the area are near Belle Fourche, SD and near Worland, WY. I bought 4,000 lbs from Worland to line an irrigation pond and have kept about 100 lbs cause it's cool stuff. The Worland mine is closer, and they crush it to a finer powder. It's also higher in calcium than the bentonite near Belle Fourche. Whatever the reason, I started mixing it with water like I would powdered joint compound (drywall) and was VERY impressed how much water it wanted to get a reasonable slump in the slurry, mixing with my industrial drill in a 5 gal pail. I then hired my grandsons (grandma cookie payment) to help me pack in the perlite in mud pies,to a breaking consistency, and cram in between my two layers of SS 24ga sheetmetal for the burner. That's when I decided on the experiment making a brick in my first RMH. I let it dry about a month before firing it. Does that help? I haven't figured out how to post picts in the place.
I just finished the burn riser for my daughter's new house with diatomaceous earth (bentonite) and perlite, mixed per the Wisner's new info and crammed between two stainess steel tubes I almost gave up bending into a tube from stainless sheet metal 24ga because I couldn't find snap lock tubes 26 ga or 28 ga. This was terrible. For experiment, I crammed some of the stiff mix into a brick let it dry and left in in my existing RMH firebox where it's hottest. Out came a cute very light brick, really quite strong. This light firebrick insulating material sure could be made commercially, so we don't even need those hard-to-get stainless steel tubes, run down the perlite and bentonite to build our own. Right?
This brings up concrete. I really like how quickly and easily cement can be mixed and poured by hand. It's especially encouraging to have the new EMC cement mix powder manufactured with much less fossile energy than traditional portland. I have just rebuilt the thermal mass out of concrete for my chimney, a bench on the floor of my first RMH using concrete I mixed by hand in a wheel barrow into blocks that conform and contact very well with the chimney: 8" sch. 40 steel pipe (about 5/16" steel). It works enormously better than the clay/sand mixture I initially plastered around it.
I am now building my third RMH for a two story house 30 X 52. It has a 6" schedule 80 steel chimney under the slab on the floor, 30' horizontally under the floor (contacting the concrete), and 19' up through the roof. I'm happy with steel chimneys and concrete thermal mass for my RMH design, but am jealous of the ambience of cob.
I'm still searching for discussion on concrete thermal mass and steel chimneys for RMH's.
I'm in process of building my third RMH doing both water heating and floor thermal mass. My first one, now into our 4th Eastern Montana winter, uses a single loop, stainless 3/4 pipe, in the firebox (overbuilt). It is thermally syphoned via copper to a 300 gal. elevated vertical steel storage tank (junk propane tank roasted to red hot over a bonfire. fun event.). Inside this tank is a 1/2" copper coil under domestic water pressure (no pressure in the tank itself), the cold water supply to the 30Amp 240V inline water heater made for tropical wells where the incoming water is not below 70F. The gravity flow no-pressure tank water connects to a pex header for four floor zones to store heat in our 14" of sand/gravel over 2" of EPS insulation, topped by our wood floor. I have a 1/25 HP conventional pex pump to loop the warm water down into the floor zones. With this system, in Montana cold cloudy windy winter nights, I never get up to fire up the stove. In 12 hours we lose less than 5 degrees F. I think there is a signficant heat loss in the fire box itself with this system, one of several areas where I lack the wisdom/research of most writers in this forum. I think it's compensated a bit with my 8" dia chimney of sched. 40 steel 42' long helping my bottle neck rocket effect in the firebox. I'm also helped with a whole-house fan (mostly for allergies) that accesses outside air increasing rather than cutting inside ambient pressure. I almost always turn it on (1 hr timer) when I start the stove, to run until the core is hot enough to rocket.
Our tank gets heat in summer, spring, and fall, rarely in winter, from a solar collector loop driven by a 120V aquarium pump through 80' black rubber hose coiled under a double glass window and over an insulated aluminum surface spray-painted with highly selective chrome-based solar collector black paint made specifically for aluminum surfaces. Both systems regulate themselves fairly well. The rubber hose in the collector is freeze-immune. A cheap 110v. AC thermostat strategically placed inside a window in an insulated pocket switches the pump on or off easily with maximize temperature swings from insolation and out radiation at this sensor pocket.
My latest RMH will have 1/2" copper coiled flat on top of the RMH barrell where the highest temperature is exposed, and from there thermally syphoned in a loop via 3/4 pex to a poly tank. I value passive systems, and if active, internally powered--and if externally powered, not overpowered or overbuilt technically. Stainless steel pipe inside the firebox is a case of overbuilding, and would make sense only if the loop were check-valved or closeable or under pressure. It's entirely 100% open. Copper coiled in the open on top of the barrell leaves room in the center for a teapot, and still gets adequate heat on stormy cold cloudy days to raise the temp on the tank. Those are some of the improvements over RMH 1 at greenwoodfarmmt.org. Others were gleaned, with lots of gratefulness on our part, from real permies writing in this forum.
Help I have been procrastinating, and cannot find info on whether a 40lb bag of refractory cement (pricey, I know) can substitute as well for my 1/2 Halverson clay 1/2 vermiculite. Our drought this summer made all my clay sources too heavy, my grandkids (and I) cannot roll it out enough to knead the insulation in and make hard "mud pies" I pound in between the two metal skins of the pipes. So a friend came by and asked why we are working so hard. Just get some refrac' cement.
This is my third rocket stove. My first one didn't work as well as my 2nd because I used well casing for the inside burner liner, and packed the rest with vermiculite (mostly against the inside well casing, 3/8"+ steel) and sand and river rock gravel. The oustide burner liner is a 55 gal drum. Over that is a discarded 30" dia industrial water pressure tank. The vent is 8" sched40 gas pipe, steel, welded and bolted (coupling) to old pressure tank, with 30' on the floor and 15' up to the elbo that exits the house. It works fine after 30 minutes of burning carefully with small wood until the core gets hot enough to rocket.
Who has worked on a design to use a high efficiency gas furnace nozzle to flame through a 1 1/2" hole in the back wall of the firebrick firebox? I'm in process on my 3rd rocket mass heater, and like this idea, but wonder what happens when the burner heats up and the draft increases. I'm concerned the changing fuel/air mix with heatup would be far more than a conventional gas furnace. My wife and I are 70-ish and sometimes in severe MT cold would like the convenience of turning on a furnace to save our pipes when we're gone. We love our rocket stoves!!
Thanks Paul. I can't tell from the video if it's long or short. It did not have footage of the attachment to the barrell, and nothing on the port through the insulation and two surfaces of the riser with the insulation in between. I'm puzzling how to keep my vermiculite/sand mixture insulating the heat riser from leaking into the fire box. My current system, in my 40X60 house, is welded steel 3/16ths or better, too robust to repeat in the 16 X 20 guesthouse. www.greenwoodfarmmt.org
I have a old window insulated solar collector made of 100 ft of black rubber garden house, connecting via a leak-sealed aquarium pump to my 250 gal. storage tank (recycled cast-off propane tank barbecued on a hug bonfire). It works fine, and freezing/thawing in Eastern MT spring and fall is no problem; the sun just melts the ice in the hose and warms it to over 90f, then the pump kicks in with the strategically-placed 110v AC T stat, and keeps our preheater tank (no pressure) above 80f. This allows a cheap 30amp 220v inline water heater to supply all the hot water needed, routed via pressure thru a coil in the big tank, for two families in our house. www.greenwoodfarmmt.org
Yes. The book was essential to designing our slightly larger variation, with open chimney-on-the-floor. I'm wondering about the strength of the pipe you used surrounded by heavy rocks/bricks. No crushing? How do you fasten the pipe to the surrounding barrel? What's the size diameter and sheet steel gauge # of the pipe? Maybe that's too many questions.....
I need help designing a small rocket mass heater for our guesthouse, 18 X 20. Was excited to see Paul's video, that rocket mass heaters have made their way into MT. See www.greenwoodfarmmt.org for our larger unit in our house/shop, it's working fine going into the third winter this fall. Amazing this site exists, and all the interest!
