[Cob] Re: My two cents about cob/earth oven also heating water etc...

[ocean]

Pondering once more how to use wood fire to heat water, cob 
furniture/floor, etc:

This opinion is informed by my experience with the really lousy metal 
Lopi wood stove in my main house, which has a 20+ foot high chimney, 
but fails to draft well even after the fire is blazing...

We really don't want a water/heat exchanger to reside within the 
primary combustion chamber of a wood stove (metal), masonry stove, cob 
oven, etc for the following reason:  any heat "pulled" out of the stove 
will result in a cooler burn, with more creosote exiting the stove and 
being deposited into the chimney.

Since unburned creosote is potential fuel, this results in the best 
case - loss of potential heat energy; in the worst case - more 
likelihood of a chimney fire!  Pulling heat from a cob oven is also not 
desirable, since we want to keep that precious wood heat for cooking 
and bread baking.

So my two cents brings me back to recommending Ianto's cob/steel drum 
rocket stove as the best and only safe scenario for external heat 
transfer from a wood fire.

In Intato's rocket, nearly 99% combustion of wood is achieved within 
the super insulated firebox and "heat riser" chambers (remember rocket 
stove exit gasses are mostly water vapor - no creosote - like the steam 
from a laundry vent); thus a metal coil heat exchanger can be safely 
placed between to two drums (outside the primary combustion chamber) or 
in the horizontal flue which flows through a cob bench or earthen 
floor.

I'm currently working on a hybrid rocket water heater design which will 
combine wood heated water with solar heated water flowing into a 
standard water heater (gas/electric), and then use this heat for 
hydronic floors and maybe even the hot tub!

BTW, I recently improved the combustion in the aforementioned lousy 
Lopi by lining the firebox with 3 inches of very sandy cob on the 
bottom and three sides (4:1 sand:clay ratio, sans straw).  After baking 
the liner dry, the previously smoldering wood stove fires are now 
blazing hot - and hence much more efficient (as evidenced by the lack 
of ash in the stove after the fire is out).  Maybe I'll post some pics, 
when I have the time...

Until then,
Happy Cob Year,

Ocean Liff-Anderson

http://www.intabas.com
http://www.peacemaking.org