Brokenfoot Ranch Ecovillage Community

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Ten, nine, eight, seven, six… May 1, 2009

Greetings from Brokenfoot Ranch!

Sorry it’s been so long since I’ve written anything here in Blogland, but I warned you that I wouldn’t write just to be filling up time and space with trivial stuff. So we all had to wait until I had something really interesting to talk about, and believe me, now I do!

So let me tell you…about the amazing visit I enjoyed
recently with Tim Kring, who built a terrific rocket mass heater in
his basement. He’s a soil scientist by profession, and obviously this
goes deep into his psyche because he sure does like playing with mud
and clay and sand and rocks, which is one of the main activities
involved in building a rocket mass heater. He and his family live in a
subdivision up north of Atlanta; and over the years, Tim has been
going deeper and deeper into a variety of sustainable, hand-built, and
homemade technologies.

Besides the rocket mass heater in the basement, I should note the
earthen floor Tim built in the same room. It’s made of packed Georgia
clay, and sealed with linseed oil. And it’s really beautiful, both to
look at and to walk on. It’s strong, it doesn’t crumble or crack, but
at the same time it feels very comfortable underfoot, sort of like a
nice path in the woods. And, it doesn’t absorb water; Tim demonstrated
by spilling some water on the floor, and the water just sat there on
top, never soaking in.

In his backyard, Tim has built an beehive oven (which he wants to tear
down and do over again using some new ideas he’s come up with), and
another construction called a Rumford oven (or was it Rumford stove?),
which cooks and heats a big thermal mass made of cob, and lets you see
the fire, too, much as you would with an ordinary fireplace. Tim has
kindly provided the following explanation of the Rumford stove, as
well as some very interesting additional comments:

“The Rumford is a fire place, just an outdoor one. Count Rumford made
hundreds of experiments on fire places to improve their function. He
is the person who invented the damper, I am told. He outlined a set of
ratios and dimensions for building a good fire place. We have simply
followed the directions and built with mud. Jasper [Tim’s son] and I
had a big fire in it Friday night, and slept out in front of it. It
will draw flames to nearly 6 ft. in height. This is quite a contrast
to the performance of the “insert” fire place in the house. Funny,
most insert fire places are really not designed for a hot fire, but
are better suited for the “fake” logs you buy at the grocery store- a
fire for visual effect, not for warming the place. I had tried to put
a quality wood stove in our home a few years ago but was told that the
a good wood stove would actually melt the chimney if we had a hot fire
in it. It seems the chimney was not rated for real use and I’ve come
to find out most are not in many subdivisions. This is one of the nice
things about building with earthen material. It won’t rot, won’t burn,
it’s free, it does not have toxic additives. No special skills are
needed. At the earth’s temperature and pressure, quartz and clay
minerals are about the most stable thing on the planet; as it’s
already broken down to its final form, it’s not going to break down
into something else- it’s done. As the old mud builders say, give the
house a good hat (roof) and a good set of boots (foundation) and it
will last nearly forever.”

Although his house already has a conventional water system and toilet,
Tim also installed a small composting toilet, a Sun Mar. But realizing
that this type of composting toilet doesn’t really work in terms of
making actual compost, he wants to replace it with one like mine (a
Phoenix). Then there’s the nifty little greywater system that filters
the water through a very pretty mini constructed wetlands just beside
the house, and then drains into an irrigation system for some trees in
the backyard. And as if all that were not enough, he’s got a space
excavated in the backyard in which he plans to build a small earthen
cottage, which will make use of most or all of these technologies.
This cottage will have a living roof (a roof covered with
specially-chosen live plants), and be seriously earth-bermed on the
south side, with the windows mostly on the north side–the exact
opposite of the regular passive solar concept. But Tim did this on
purpose–to stay cool in summer without air conditioning. He says that
with a rocket mass heater built into the cottage, heat during the cold
months won’t be an issue.

Tim’s two sons, one in his teens and the other who seemed to be around
10, like to help with many of these projects, and it’s great to see
kids coming up learning all this stuff. It seems they set a lot of
store by these achievements, too, because they get worried when their
dad talks about tearing out his creations so that he can rebuild them
to try out new design improvements! Well, for sure he is all about
doing and learning, and preserving past works comes second.

And basically, almost nobody in Georgia is aware of what this guy is
doing! To really talk shop Tim has to go to Oregon and hang out with
the originator of the rocket mass heater, Ianto Evans, and the other
folks there at the Cob Cottage Company. They give workshops
periodically; I wish I could go!

So, by now you are no doubt itchin’ to know, just what is a rocket
mass heater??? Well, it’s a kind of wood-burning stove designed and
installed to capture a lot more useful heat for a dwelling than is
possible with an ordinary fireplace or woodstove. With a conventional
fireplace, most of the heat just goes up the chimney; unless you sit
very close to the fireplace and the fire is roaring, you won’t get
much benefit. And even if you do sit close, it’s mostly your front
side that gets warm, while your backside stays cold. And across the
room, pretty much the only benefit will be the cheerful sight of the
homey hearthside with its fire merrily crackling away. Sometimes this
situation can be improved by adding fans to circulate the hot air away
from the fireplace and out into the room.

Then there’s the woodstove, which is usually somewhat better in terms
of efficiency in putting heat where you want it. A woodstove is
usually a heavy metal box of some sort, iron or steel I suppose. So
when the fire inside gets going, the metal heats up and radiates heat
all around itself. After awhile this radiant heat can warm up most or
at least some of your house (depending on the size and configuration
of the house, and the size and placement of the woodstove in relation
to the these features). But, even with an “efficient” woodstove, like
mine, that has a catalytic combustor (a device which increases burn
efficiency) in it, I still go through quite a lot of firewood. My
house is so tight and well-insulated that running the woodstove can
get me temperatures into the upper 70’s, throughout much of the house.
So I usually don’t fire up the stove except in really cold weather.
Even so, this winter season I’ve gone through a lot of wood; I can’t
tell you how many cords, because we split it here (around the first of
December) and just stacked it up along the inside wall of the barn and
never measured the dimensions. But it was a lot, and I estimate that
at least half—maybe two-thirds–of it is already used up.

My stove pipe is very tall, going from the woodstove on the main floor
on up through the second-story ceiling/roof. Since most of the
stovepipe is inside the house, the stove’s heat has a big surface area
from which to radiate into the indoor environment. In contrast, most
ordinary chimneys are outside the house and therefore can’t contribute
much of the fireplace heat to the living space.

Anyway–and here we should bring in the horn section!–enter the
rocket mass heater! It’s based on the rocket stove, a nifty cookstove
originally designed to help low-income people in developing countries
to conserve their forests, to protect human health from ongoing
exposure to the particulate matter and gaseous products of inefficient
combustion, and to save time, energy, and/or money they were
accustomed to spending to obtain adequate firewood. Briefly, a rocket
stove usually consists of a vertical “feed” tube, into which small
pieces of dry wood are inserted; a horizontal burn chamber, where the
combustion takes place; a vertical heat riser (heat exchange barrel),
where heat from the burn chamber heats up a metal drum which is
considerably larger than the feed tube; a long, usually horizontal
(and often serpentined or doubled-back) flue pipe which carries the
hot gases from the vertical heat riser through a heavy mass structure,
often a bench, bed base, or floor, made of cob and/or a mixture of
materials such as stone, firebrick, clay, and cob. These heavy
materials slowly absorb the heat passing through the flue pipe, and
then slowly radiate this heat into the room.

But unlike the dangerously high temperatures of your metal box
woodstove (the touching of which equals a serious burn; don’t let
little kids loose in a room with a fired-up woodstove!), the
temperatures of your rocket mass heater bench or bed or floor are safe
and comfy. You can sit or lie or walk on them and pleasantly warm your
body. And this heat is retained for long periods, even several days
after the fire has gone out. (While the feed tube and the horizontal
burn chamber are also normally buried in cob and/or other heavy mass
materials, the heat riser barrel can be left partially exposed to
generate quick radiant heat into the room, and the top of the barrel
gets plenty hot enough for cooking.)

After the hot stove gases pass through the entire length of the flue
pipe, they have given up almost all their heat into the mass, and exit
through a vent or exterior stove pipe at temperatures often less than
200 degrees Farenheit. There is virtually no smoke produced with these
rocket mass heaters, and the amount of wood required is only about a
fifth to a quarter of what you would use in a woodstove! You can run a
rocket stove or a rocket mass heater on small dry branches, the kind
of deadwood easy to find and pick up in many forest areas. So fueling
a rocket requires little or no cutting down trees. This is great news,
especially in places where the demand for firewood is causing serious

Actually, I found out about Tim Kring through Cob Cottage Company.
Recently, after rereading their book, Rocket Mass Heaters,
Super-Efficient Woodstoves You Can Build (and Snuggle Up To), it
occurred to me that I should get in touch with them and see if there
were anyone in the Atlanta area who was into this stuff. So I called,
had a wonderful conversation with a guy there named Max Edleman, and
voila! Plus, Tim Kring is good friends with another soil scientist,
who lives…guess where? Around here, I’m not sure exactly where,
either in Carrollton or in Bremen, I think. And they talk to each
other practically every week. So Tim and his family visit Carroll
County from time to time. And I even met this local soil scientist
once, when I did a program on intentional communities and the
Brokenfoot Ranch project, last June at the Carrollton library. Anyway,
small world!

To find out more about rocket mass heaters, assorted other rocket
stoves, and cob construction, check out the website of the Cob Cottage
Company at There are also sites that show how to
make a simple rocket stove, such as and The
stoves have attained considerable reach in Mexico and some other Latin
American countries, where they are variously called Lorena (a
contraction of lodo, mud, and arena, sand —indicating the materials of
which they are built) stoves or Patsari stoves. If you “google” the
term “rocket stove”, you can find other sites in both English and
Spanish about these stoves.

And, last but definitely not least, you can reach Tim Kring at his
e-mail address, He says he is happy to talk to
people who are interested in these technologies. Thank you, Tim!

Best wishes to everyone,
Myra Bailes