Cob: cob bench heater

[Shannon C. Dealy]

On Wed, 6 Dec 2000, Louis wrote:

> Does anyone know about the efficacy of this cob bench heater?  This showed 
> up on the essa list as being a downdraft design made from a barrel.  I 
> wonder if it would be a less costly alternative to a true masonry 
> heater.  How well does cob hold up with really high temperatures?  This is 
> something I've been a little skeptical of.
> Louis
> 
> http://www.proaxis.com/~deatech/cobcottage/pics/michael.jpg

The cob does fine, firebrick is used to line the high temperature areas of
the stove design and ash (or other natural materials) is used as an
insulator.  All of the really high temperatures occur in the barrel, the
temperature of the exhaust passing through the bench is much lower.  Of
course, over time, some maintenance will be required and it may be
necessary to pull the barrel and reconstruct the combustion chamber and
chimney inside the barrel (even commercial wood stoves burn out over
time).  The highest temperature occurs at the bottom of the barrel where
combustion takes place, but this is well lined and insulated.  The
exposed top of the barrel gets the heat straight out of the chimney
(making it a good place to cook or keep your coffee warm), from there, the
exhaust travels down along the outside walls of the barrel and into the
bench.

Here is a really crude drawing of the downdraft bench stove.  It is not
completely accurate :-) due to the limitations of ASCII art, but it should
give you a general feel for where the heat is .



         Barrel top              - outside exhaust -
         Exposed hot surface          | |
           V                          | |
wood   _________                      | |
  V    |        |                     | |
|   |  |  |  |  |_____________________| |
|   |  |  |  |  |  Cob Bench          | |
|   |__|__|  |  |_____________________| |
|   _________|_______exhaust____________|
|___|   ^^^
        Combustion chamber



Shannon C. Dealy      |               DeaTech Research Inc.
dealy at deatech.com     |          - Custom Software Development -
                      |    Embedded Systems, Real-time, Device Drivers
Phone: (800) 467-5820 | Networking, Scientific & Engineering Applications
   or: (541) 451-5177 |                  www.deatech.com