The JUCA design uses a different design
concept. Instead of needing a kindling type fire that has to be
held back, the best use of a JUCA involves using large diameter
un-split logs (up to 10" in diameter). These could not be
used in other wood-burners because they don't burn as furiously
as needed for a radiant wood-stove.
The Argument Against Air-Tight Operation
Modern woodstoves are generally of a type called "AIR-TIGHT."
This means that the fire is controlled by suffocating it -- the less
air, the less flame. This was certainly an improvement over previously
available wood-burners that were basically uncontrollable with
short-lived fires. The suffocation of the fire prevented the rapid
burning of the wood, making it burn more evenly and making it burn
longer. These advantages of air-tight stoves have led to a common
belief that only air-tight stoves are any good. There is merit in
this belief except for products like the JUCA that operate on a
These air-tight stoves have some bad side-effects related to
their suffocation principle of operation. The lack of air causes
the fire to burn incompletely. In the case of a kindling fire
being really held back fully one-third of the energy available
doesn't get produced -- it goes up the chimney as unburnt gases,
primarily carbon monoxide and creosote vapors.
Both of these gases are formed any time you burn wood, but a fire
with plenty of air will produce only one-tenth as much as the same
fire being suffocated. If any part of the chimney is "cool" (less
than 300°F or so) then the creosote vapors can condense on the
chimney walls. The solid creosote built up is basically proportional
to the amount of vapors in the smoke. This means that air-tight
stoves can cause creosote to accumulate in the chimney up to ten
times as fast as an open stove would.
This accumulation can occur so rapidly that it is amazing. There
have been cases of new chimneys being totally clogged with creosote
from an air-tight stove in ONLY 3 WEEKS. There are two dangers
in this happening. First, the creosote could catch fire. This is
called a chimney fire, and such a fire burns so violently that
if the chimney is not perfectly sound, the heat could endanger
nearby house framing. The second creosote danger is that if the
chimney gets clogged, the large amounts of carbon monoxide produced
by the air-tight stove has nowhere to go but out into the house --
a very dangerous possibility.
These reasons are why all wood-burner suppliers (including JUCA)
ask owners to regularly check their chimneys for accumulations of
creosote. As long as this is done, and the chimney cleaned as
needed, there would be little safety hazard. The problem could only
occur if accumulations build up. The choice of an airtight stove
that may require WEEKLY cleanings (if the government has its way)
or a non-airtight wood-burner that may only need to be cleaned
once or possibly twice a year, somewhat combines the questions of
safety and convenience.
The JUCA can use them because
it is not a radiant device but rather a forced-air wood furnace.
Even the limited heat from such large logs burning can fully heat
a large house because of the extensive and sophisticated heat
exchangers in the design. Large logs give even, constant output
over LONG periods of time without having to suffocate the fire.
If air-tight stoves used such a good heat exchanger, they would
compound the problem of creosote by cooling the chimney even
further causing even faster accumulation of creosote deposits.
This is also why air-tight stoves cannot have large blowers
Since the JUCA burns relatively freely, the smoke has
little creosote vapor in it. The small amount present does tend
to condense out, partly in the stove itself, but the rate of
creosote buildup is VERY much less (about 0ne-fifteenth) than that of
an airtight. Additionally, the safe upper limit of efficiency of an
airtight (about 55%) doesn't apply to non-airtight stoves. The JUCA B-3B
safely operates at about 80% efficiency.
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