Very efficient, Kawagama consumes only about a cord and-a-half to two cords of a
combination of hardwood, pine, and hemlock to fire it off. This seems like a lot
of wood to a non-woodfirer, but if it were a single chamber kiln of the same total
interior size it would consume far, far more wood.
Wood for Kawagama must be at least a year old and very dry. A lot of attention is
given to the wood supply, and plastic tarps are repeatedly taken off and placed over
the wood as the weather patterns change to allow good drying.
The wood is pretty finely split with the largest diameter pieces ever used being
similar in diameter to a construction four-by-four. As stoking progresses, the diameter
of the wood selected goes down. At the end of stoking each chamber, the pieces are
frequently less than about one and-a-half inches in diameter, and they almost vaporize
as they hit the 2400-2500 °F temperature in the fireboxes.
Surprising most people who heat homes with wood, softwood is a choice wood for many
aspects of kiln firings rather than hardwood. This is because it releases its heat
energy quickly. Hardwood, which burns slower, is used in the earlier stages of the
firing when John is trying to hold the kiln back in the rate of temperature climb.
Usually the last few degrees when approaching 2400 °F in the general chambers are
the hardest to attain, as heat loses become significant. Finely split softwood at
this point in the firing helps squeeze the last little bit of performance out of
the kiln. At this point, John hand selects the smallest diameter and driest pieces
of wood for the final stoking of each chamber.
Cooling is normally about 72 hours, depending a bit on the wind velocity in the
area, so the whole firing cycle, from cold to cold, takes about five days. The cooling
rate has a lot to do with the look of the fired work. The middle two chambers cool
a bit slower than the ones on the ends of the kiln, because they are ”surrounded”
by the hot refractories on either side.