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 reduced creosote.

  • 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.

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You might want to try:

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.)


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.

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.

The JUCA Home Page is at: juca