Cob Masonry Stoves

[Robert Bolman]

Speireag writes:

    In my ongoing quest for the perfect construction, I have run across
references to masonry stoves, but no good definition for one.

    How do I make one?  Must I buy one?  What are the parameters?  What
must I allow for in construction?  Are they all huge?


I too have an ongoing quest for the perfect construction.  On that quest
I've also looked at masonry heaters.  They can be very expensive - enough
so that I wouldn't feel comfortable spending that kind of money - even if I
had it.  There are kits made up of pre-cast refractory modules for a design
called "contra flow" that stack up relatively easily to form the basic core
which then will presumable be covered with brick or tile.  I personally
would consider covering the thing with cob.  You'd probably want to have
some kind of a thin expansion membrane to avoid cracking, but after that
you could make the thing as massive or creative as you wish.

Given that much of the charm of a radiant heated slab is in having the
warmth where it is in frequent and direct contact with the human body,
there is a good argument for the heated cob bench as built by Cob Cottage
Company.  Having little direct experience with them, I worry that the down
draft combustion system that they typically employ can be problematic. 
Also, I was recently unable to get one through the City of Eugene Building
Department.  They have never been suitably tested.  Still though, they seem
like a good idea.  I think of it as the poor person's masonry heater. 
Instead of possibly thousands of dollars in fire brick, you're talking a
few dollars worth of scrap steel parts and a lot of earth, sand and straw. 
Being in the form of a bench, the heat is pleasurably applied to your butt.
 Due to the massiveness, the heat will presumably be retained for many
hours after the fire goes out - especially if within a straw bale
structure.  If designed well, little or no smoke will be visible exiting
the chimney and the exiting gases will be about 300 degrees (F) -
relatively cool meaning that the heat has been left where it's supposed to
be.

Any combustion enginoids care to run with that one?  I could go into
greater detail about the down draft combustion.

Robert Bolman