The bell stove concept has been understood in Russia for many years, (Mark Twain described stoves using the concept when on a trip there in the 1860s) and thousands, if not millions of working stoves have been built there. Only recently have they been more widely appreciated in this country. In 2009 workshops on the bell stove in America made folks here more aware of the concept and a few have been built.
BELL STOVE (the earlier discussion of the rocket stove is included below this discussion).
This new design for an efficient wood burning stove is simpler, easier to build, possibly more efficient, and more flexible than the rocket stove.
A bell stove can be built large or small, to heat a shed or a large house. It can be built in many shapes.
The key concept of the bell stove is a bell or series of bells of metal or brick or blocks that trap and hold heat within the bells. Heat rises, so heat from a fire will rise within a bell and the hottest part of the bell will be the top. A series of bells are connected at the bottom by the passage for flue gasses from the fire. The bells are open to the flue passages at the bottom. The flue gasses, after passing beneath the bells and giving up heat to the bells as they pass exit at a conventional chimney connected at the base of the last bell. The passages need not be all of the same square foot sectional area, as in a conventional rocket stove. The area can vary. And, the bells can be large or small.
I was in the process of building an oversize rocket stove with a 144 square inch (12 x 12 inches) cross sectional area throughout the stove and chimney. Now I intend to modify the design to become a three chamber bell stove with the flue passage below of only 8 x 8 = 64 square inches. The smaller flue size (along with the bells) should result in less heat loss through the chimney.
Essentially, a bell is a heat exchanger, but more flexible and perhaps simpler to to design and build than the long tubes of the conventional rocket stove (described below). Size ( in square foot area of the flue pipe) of the exhaust path need not be kept constant as in the rocket stove. At the openings from the flue path into the bells the area of the flue expands to be as large as the bell. In tests no upper limit to bell size has been determined - (no point where the stove doesn't work because the bell is too large has been found so far). What occurs is - heat and gasses flow into the bell from the burn chamber through the opening between them, get trapped in the bells, (where they give up heat to the bell) and as pressure increases find their way out through the (second) passage to the next bell, or, at the last bell, to the chimney.
The chimney: experiments
The chimney, in my opinion, as a result of experiments is a big part of the reason a bell stove or rocket stove works. In experiments, I have built a long passage with the passage turned vertical at the end (a chimney, another-words), lit a fire inside the end opposite the chimney and watched as the smoke puffed out of the burn end (the wrong end) for a moment, and then, finding the chimney, sendng the smoke, (all of it) to the chimney.
I have done this at two scales small and large. The small design was simply an all brick passage only 4 inches square and 4 feet long, with a chimney of bricks only about 12 inches high at the end. The large design used large and varying passages: 12 inches square at the opening to the burn chamber, ( where wood is loaded and air flows in to the fire), 22 inch diameter passage through 3 barrels (96 inches horizontal distance) laid horizontally and open at the ends, then an 8 inch flue passage at the end (opposite the burn chamber) to the chimney, the chimney of two 30 gallon - 13 inch diameter barrels stacked on top of each other. This chimney is only about 5 feet high. In both designs, after a puff of smoke through the wrong end; proceeded to burn as long as I fed fuel to the fire (hours in the case of the large design) with the smoke all exiting through the very modestly sized chimneys. I do not know the point where the chimney becomes too short or too small in diameter to work.
Therefore, a very modest and inexpensive, and safe chimney can be used with these designs rather than the long, expensive and dangerous (if they burn through as they too often do) chimneys used with conventional fireplaces and wood stoves that go through the roof of a house.
The structure of the large design ( with bell type chambers rather than horizontally laid barrels) would be built beside the house in a fireproof shed, with loading from outside the house (so the initial puff of smoke does not go into the house) and the chimney on the side of the shed opposite the house. Bringing heat into the house from the shed is detailed below.
This is an introduction, more later:
Here, below is my earlier discussion of the Rocket stove.
Rocket Stove: design for an average-sized house
Rocket stoves, until now, have been designed and used in "cob houses", tiny mud and straw houses that are cute and efficient, but not likely to be widely adopted by the conventional American family. Can a rocket stove be upgraded to become a widely used heating system for a house of say, 1500 or 2000 square feet?
Here is how:
A rocket stove essentially has three components: burn chamber, thermal mass, and chimney. In this design the rocket stove would be built in a fireproof insulated shed adjacent to the house to be heated. This shed might be as small 10 foot x 10 foot x 7 feet high for the design described here.
The burn chamber:
The secret of the stove, revealed here or in web sites if you do a Google search of rocket stoves is that the burn chamber, where the wood is burned IS INSULATED. Why do that? Don't you want the heat to go into the room? Because the insulated chamber means the fire can burn very hot, and therefore burn very cleanly, burning up all of the gasses and volatile materials in the wood. Because of the high temperature, the burn chamber core should be built of firebrick. If iron or steel walls/chambers are used, perlite or vermiculite around the walls/chambers can take the high temperature and insulate the burn chamber. (A small 'cob house' rocket stove uses 30 and 55 gallon barrels for part of the burn chamber). A burn chamber of about 3 square feet: 12 inches x 12 inches x 36 inches should be enough to hold a load of wood adequate to heat a well insulated house for 24 hours (equal to about 350,000 BTU of energy).
Calculation: 15 million BTU in a cord of wood equal to 4 x 4 x 8 feet or 128 square feet or 15 million/128 = 118,000 BTU per square foot or 354,000 BTU per 3 square feet. The fire would be started once a day and allowed to go out after the initial load is burned up.
Thermal mass: Thermal mass would store the heat as it travels through the flue system to the chimney. A long series of passages through the thermal mass through which the flue gasses flow would extract the heat from the fire. These passages would be 12 inches square - the same as the burn chamber (a design requirement of rocket stoves is - the flue cross section must all be the same throughout the system from burn chamber through chimney exit).
NOTE: As described in my bell stove update above, these passages could be replaced with bell chambers thus allowing a simpler, more flexible and more easily constructed design.
The thermal mass could be cheap: of mud, gravel, rubble, sand, any heavy fireproof material that can store heat. Expensive firebrick, or brick in general need not be used. The flue gas passage needs to be able to take a high temperature near the burn chamber but can be of ordinary brick or even concrete or concrete block further away, where temperatures are cooler. The passage for flue gas would wind through the thermal mass to the chimney.
Area of the thermal mass required to store 350,000 BTU of energy per day: Sand/mud/gravel/concrete can store 22 BTU of energy per degree per cubic foot. So thermal mass at 120 degrees average temperature after a burn, losing 50 degrees over 24 hours would release about 1100 BTU per square foot (22 x 50) as it cools down to 70 degrees. Thus 350 cubic feet of thermal mass would store 350,000 BTU of energy. An area of 10 feet x 10 feet x 3.5 feet equals 350 cubic feet.
Heat will be moved from the thermal mass into the house using a fan or fans pulling air through a chamber (and through openings into the house) above the thermal mass passages. This chamber - equal to the area of the thermal mass or 10 x 10 x 3.5 feet takes up the area of the upper half of the 10 x 10 x 7 foot high shed.
The chimney: The chimney can be of ordinary concrete block since most heat is lost in the thermal mass before the chimney is reached by the flue gasses. In a carefully designed system the exhaust gasses at the chimney top should be cool enough so your hand would not be burned if you put it over the top. The chimney would be located on the wall of the shed opposite the wall adjacent to the house. The chimney need only be 10 feet tall - three feet taller than the height of the shed. The cool flue gases make a low chimney close to the house a safe proposition.
Building codes require that the chimney be 3 feet higher than any roof within 10 feet of the chimney. The chimney on the opposite side of the shed from the house fulfills this requirement.
I expect to replace my corn stove and heat pump with this rocket stove system, keeping the old systems as backups. I expect to build a 500 square foot solar collection system using recycled materials to heat my house on sunny days in cold weather so I need not fire up the rocket stove every day.
I can obtain almost unlimited wood for this system from dead elm trees, dead ash trees, pallets, and other downed and wasted wood such as power line tree trimmings. Thus my heating bill could be reduced to ZERO, moving me closer to my goal of Zero Cost Living.
Modify the house to incorporate a hydroponic solar greenhouse for food production to eat and/or sell. 200 square feet of greenhouse might provide 2,000 pounds of produce (at 10 pounds per square foot) worth $2,000 to $4,000 dollars or more per year.
Your food requirements, property taxes (if you build in the right, low tax location and build a practical no frills house), and some other costs could be met by the income from the greenhouse.
As described in my book and elsewhere in this web site, it is possible for one person to eat well for a few hundred dollars a year.
Additional improvements to the house could reduce or eliminate other expenses such as the pesky and numerous 'miscellaneous costs' (as I call them) such as furniture, clothing, media, household, kitchen, bath, yard, and recreation costs.
So you may be able to approach Zero Cost Living by building your house in a suitable location and in the proper way.
You will still have some expenses and so may require a business, job (God forbid), investments, etc. But they can be modest.
