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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 different principle.

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.

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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 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 safely.

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.


The JUCA Home Page is at: juca