A fire is started burning in the main firebox and the hot gases and flames pass
out of the firebox into the first chamber. They pass through the stacking of pottery
on their way to the first chamber’s exit flues, and give off their heat energy to
the pots and kiln walls on the way through. The effectiveness of this heat transfer
is based heavily on the differential of the temperature between the hot gases and
The gases exit the first chamber a bit colder than they entered it, because they
have given off heat energy to the kiln’s structure as well as the wares in the chamber.
They then enter into chamber two, where the ware itself will be far colder than
the ware in chamber one. So the gases exiting chamber number one can still effectively
give off some remaining heat energy to that relatively cooler ware on their way through
the second chamber. This same process continues on through each successive chamber
up the hillside.
In a sense, all of the chambers after chamber number one are firing on waste heat
that would have gone up the chimney if chamber one were a single chamber kiln. This
makes for extreme efficiency in the use of the wood's heat energy! Because each
successive chamber is cooler than the one upstream of it, the gases can still give
off more of the remaining heat energy all the way up the hill.
When chamber one is completed firing to temperature, stoking ceases on the main firebox,
and wood is now thrown into a smaller firebox located right near the inlet flues
of chamber number two. The air for combustion of the wood in chamber two is now coming
through the main firebox and chamber one...... so the heat already stored there is
now being moved up the hillside into chamber two as the combustion air is pre-heated.
This provides more efficiency!
Up the hillside, at the top end of the kiln, the final chamber's exit flues can either
just end at the floor height of the chamber, or they can be ducted together into
a short vertical chimney. The former was much more common in historical Japan, while
short chimneys are certainly the rule in the few of these style of kilns that are
located here in the United States.