Air-Limited Operation of a JUCA

First, note that JUCA woodburners are designed NOT to be air-tight. However, it is possible to operate a JUCA in an air-limited mode that is similar to the intended operation of an air-tight stove. We do not encourage this way of using a JUCA, but since some people are likely to use this way, we will discuss what to do.

  • FUEL: When operating in an air-limited mode, your wood should be 4-6" diameter or split to that effective size. It should be cut to 16-24" length, split if necessary, and seasoned (dried) for at least 9 months.

  • FIRE SIZE: The fire should always be built near the back wall so that there is at least 9" between the wood and each glass panel. Gauge this by a full hand-span from fingertip to fingertip. IN OTHER WORDS, IN THIS MODE YOU SHOULD ONLY BUILD A FIRE 16" wide by 12" front to back. (F-9AX, center fire in firebox)/(K-3, 8" front to back)

  • GRATE: You may want to use a wood grate to retain the wood and to raise it up so air can get under the fire. The fire will burn more completely on a grate; however, it won't last as long. THE SIZE GRATE YOU SHOULD USE SHOULD BE BASED ON SECTION C ABOVE - i.e. 16" x 12" for MOST MODELS. It can be a basket grate with a flat bottom.

    If you do not use a grate, the fire will be harder to start, but it will burn longer. Make sure fires are only built in the hearth area described in section C above.

  • STARTUP: Put in a few twigs, branches and some wadded-up newspaper. Then put on three or four pieces about 1 to 3" diameter. Light it, close the door and leave the draft control at least halfway open. After about 3 minutes, add two or three larger diameter pieces of wood and close the manual draft control to about a 1" wide opening. DO NOT USE GASOLINE OR ANY FLAMMABLE STARTER.

  • OUTPUT CONTROL: The draft control may be adjusted to partially control the fire. If the house is getting too warm, closing the draft control will reduce the air flow to the fire and thereby control the fire intensity.

    Since the unit was designed for fuel-limited operation, it intentionally has a "looseness" so that a flow of air is always present to reduce creosote and pollution. Using it as an air-limited unit only moderately controls a fire.

    Added to this effect is the time lag due to the large firebox volume. If you close the draft control, it may take more than 2 minutes to consume the air already in the firebox.

  • WHAT TO EXPECT: You can get all the heat you could want. The blower should turn on 3 - 5 minutes after starting the fire. See section (8) for what to expect of airflows and temperatures.

  • LENGTH OF BURN: This will depend on wood piece size, air supply, type of wood, total quantity of wood, and even the way the wood is stacked. Commercial-sized split wood will give you good output for up to about 3 to 6 hours.

  • COMPLICATIONS: The evenness of heat output and length of burn will not be outstanding. By restricting the air supply to the fire, you cause the wood to burn slightly incompletely. This reduces combustion efficiency, and also sends some unburnt material up the chimney as creosote, a black, tar-like material. If this was allowed to accumulate, it could eventually catch fire and present a safety hazard. Therefore, it is very important to regularly check the chimney for accumulations of such deposits.

  • FOR SMALL OUTPUT: - Operating any woodburner by restricting air supply can cause a lower limit to the heat output you can actually use. For large units such as a JUCA, this is often over 10,000 BTU/hr. Therefore, use of this mode on relatively mild days can be difficult - either overheating the house or having the fire go out. A solution is at hand, however. Use a "startup" fire (Section e above) in the morn ing without adding large pieces, and you will get a shortterm (maybe half-hour) fire to take the chill off the house.

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