Cob: Re: cob bench heater

[Robert Bolman]

>Does anyone know about the efficacy of this cob bench heater?

In the best of all worlds, the heated cob bench would be an effective
poor-man's masonry heater.  It would burn a relatively small amount of wood
fast, hot & clean.  The heat would be "embedded" in a cob bench which would
then be fun to sit on.  Ideally, one 45 minute burn would heat the building
for 12 - 24 hours.

I've never lived with a heated cob bench.  I expect that those that do have
them learn their idiocyncracies and that they make a fine way to heat an
offbeat, counterculture home.

I worry that if we were ever to try to get one "approved" by a testing
laboratory so that it could be permitted, the testing laboratory wouldn't go
for it.  I expect that they would have misgivings about three things.

1) There would be some question as to whether the heated cob benches "draw"
sufficiently to not have there be worry of combustion gases spilling back
into a home.
2) There would be some question as to the longevity of the "rocket elbow"
which is made out of thin stove pipe and yet has to withstand intense heat.
3) There would be concern about creosote buildup in their minds - although
not so much in my mind.

When I do a heated cob bench (summer/fall of 2001), I tenatively plan on
making some modifications of the common design:

1) I would plan on building the "rocket elbow" out of a castable refractory
(firebrick).
2) I would consider increasing the distance the flu passes through the cob
bench area to guarentee a ful heat transfer.  To remedy the obvious concern
over that modification reducing the "draw" of the stove, I would
3) Introduce a little blower to aid in combustion - a more attractive option
now that we're "post-Y2K".

I would like to have a heat sensor that would shut the blower off when the
combustion cycle is complete.  Ideally, you would load a known quantity of
wood into the thing and starting it going.  It would burn fast, hot & clean,
fully placing the energy content of the wood in the cob without creosote
buildup and then shut itself off.

Rob