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Fuel-Limited Operation of a JUCA
This is how a JUCA operates best. However, many commonly accepted
woodburning procedures are not used. Experimenting may be
necessary until you get fires that don't go out and that supply
the proper amount of heat. But it will be worth it in
increased efficiency, evenness of heat output, burn time and
- FUEL: To correctly operate in a fuel-limited mode, you
will use full logs (unsplit) ranging in diameter from 6"
to 10". The wood should be cut to 24" length (16"
length for models K-3, B-3J, B-3JN, B-3N) and seasoned
(dried) for at least 9 months.
- FIRE SIZE: The fire should be built near the back to
allow 6" between the wood and glass. Large log fires are
less intense and less likely to roar up out of control.
Also, the fire usually exists only between the logs.
- GRATE: You may want to use a SELF-FEEDING GRATE in this
mode. The front and back of self-feeding grates slope
toward the middle. When large logs are burning, they
generally only burn in between. After they have been about
a third consumed, they might roll apart. The self-feeding
grate encourages them to roll together. If they do roll
apart, the fire will probably go out.
- STARTUP: Use the startup procedure described for air-limited
operation. After the fire is established (maybe 20
minutes) add full logs as necessary, GENERALLY TWO AT A TIME.
A single large log will nearly always go out. You need two
near or against each other with the fire between them.
- OUTPUT CONTROL: The draft control is not generally used
in this mode except during startup. Leave it about 1"
open. You will control the heat output and length of burn time
by selecting the log diameter and the number of logs
loaded. This will take experimenting to find the correct
loads for your house and each specific weather condition.
It might not be a bad idea to make notes of outside
temperature against successful load descriptions. Since
your house and climate are unlike most others, we can give
you only the most general guidelines to start you off.
You'll have to adjust for your particular application.
|50°F.||Startup Fire only to take chill off|
|40°F.||2 logs 10" diam. (burns slowly for about 16 hr.)|
|30°F.||2 logs 9" diam. (burns slowly for about 12 hr.)|
|20°F.||2 logs 8" diam. (burns for about 10 hr.)|
|10°F.||2-3 logs 7" diam. (burns for about 8 hr.)|
|0°F.||3-4 logs 6" diam. (burns for about 7 hr.)|
|-10°F.||5-6 logs 6" diam. (burns for about 7 hr.)|
- NOTES: The diameter of the log is most important in the
LENGTH OF BURNING TIME. Type of wood and dryness are also
important. Well seasoned oak was used to establish this chart.
- The TOTAL SURFACE AREA ON FIRE is most important in
establishing the HEAT OUTPUT. Smaller diameter logs will
have more surface on fire and therefore give out more output.
-Except for the last two hours, the heat output will be very
By thoughtful selection of pieces for your wood load, it is
also possible to obtain a heat output well below the lower
limit than normally exists for an air-tight stove.
- WHAT TO EXPECT: The air coming out of the side outlets
may not seem especially hot. Even warm air at 100°F
feels cool when it is moving rapidly. Just remember that
your 70°F house air will be raised to that 100°F
continuously for many hours. You may find that, having
built a fire with a nice warm feeling output, after a few
hours the house might start to get too warm. In other
words, even a lukewarm feeling output may be all that is
necessary to heat your house in this mode.
The blower may take up to 10 minutes to initially turn on.
If it shows a tendency to occasionally turn off then later
on again, either have the installer re-adjust the FAN ON
and/or FAN OFF settings of the bonnet control down 5F
(have him follow the ELECTRICAL section of the INSTALLATION
INSTRUCTIONS after having shut off the electricity; or just
set the bonnet control on MAN [manual].)
- LENGTH OF BURN: This is dependent on the diameter as
shown in the chart in section f above. We have a preference
for 8" diam. logs since they usually last about 10 hours.
That means if you feed it at 8 hour intervals (say 7 am,
3 pm, 11 pm), you put the new logs on a good strong fire
that will still produce heat for two more hours. This gives
the new logs two hours to heat up and take over. The overall
effect is to give remarkably constant heat output 24 hours a
day. We have had a number of owners say that the evenness of
the house temperature was BETTER than the gas or oil furnace
they used to use.
By the way, this is good usable heat output. You will find
it possible to still have some hot coals after 24 hours but
there is less practical heat available from them.
- COMPLICATIONS: Starting a fire of 8" diam. logs can be
a pain if you let it go out. If you put in a load for a
cold day and the weather becomes rapidly milder, then the
house might get warmer than you want. Strangely enough, you
may awaken to a house warmer than when you went to bed if
this happens during the night.
Many of the normal complications of wood-heating are reduced
when using this mode. Evenness of heat output, length of
burn time, combustion efficiency and creosote formation are
greatly improved. (Even though less creosote is produced,
still check the chimney for accumulation of creosote
This will generally involve very thick pieces of wood, but
allows a way of using it on relatively mild days when most
woodstoves can't be used. On unpredictable mild days,
however, we suggest using only a "startup" (section e of
air-limited description) to take the chill off the house.
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