JUCA - Beyond Air-Tight

When cave man first discovered how to control fire he probably just used a bonfire to warm himself. Eventually he probably built a fire against a rock wall, and noticed that he got warmer with the same size fire and that after the fire went out the hot rock of the wall continued to warm him. Conventional masonry fireplaces were (and still are) built on this principle. By trial and error people settled on the best shapes and sizes. In the eighteenth century, cast-iron wood burners such as the Franklin stove became available. They heated up faster, were cheaper, easier to install and gave off more heat than a masonry fireplace. Wood burned up quickly and the alternation of roaring fire and no fire caused great fluctuations in room temperature.

Airtight products were developed next. Partly suffocating the fire made it burn longer and reduced over-heating. Since the smoke moves more slowly, it had more time to transfer heat to the metal of the stove, thereby increasing efficiency. An important side effect was soon noticed. The suffocating wood did not have enough oxygen available to burn well. Some unburned fuel was going up the chimney - under some conditions quite a lot. This hurt efficiency, of course, but it also allowed a lot of these unburned gases to condense on the cooler chimney walls as creosote accumulations. If the creosote ever catches fire, it burns very fiercely possibly endangering the house. Rapid creosote formation is a natural result of air-tight wood-burning.

In principle, the addition of air just above the fire (secondary combustion air) should allow the unburned gases to now burn. Since it hadn't burned because of lack of oxygen, by now injecting air the combustion should become complete. Unfortunately, no. The main chemical reaction that must occur will only happen above 1211°F. Under 1211°F, no reaction can happen. Numerous studies have shown that existing products on the market do NOT have effective secondary combustion systems. At best they work maybe 20% of the time.

Another idea promoted to cure the air-tights' creosote problem is the catalytic combustor. The idea is to reduce the required 1211°F down to say 600°F so that secondary combustion was more likely. Independent studies have shown that actual products fall short of the claims made for them. The improvement in performance is due mostly to the smokepipe restriction making the smoke stay longer in the stove rather than improved burning. An independent TVA study concluded that the only reason a catalytic combustor should be considered is for air purity. The improvement in efficiency or creosote is minimal and not worth the substantial cost of the catalytic device.

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Until about 1970, mankind didn't know a whole lot more about burning wood than cave man did. It has always been "try it and see what happens." Since 1970, rapid progress has been made in many areas of woodburning technology and theory. Unfortunately, most of the products actually on the market poorly represent these advances. It is surprising how few manufacturers actually understand how and why their own products work. Remarkably few have any science or engineering background to design stoves and furnaces.

The JUCA principle of operation was developed by an individual whose educational background was in nuclear physics. Much attention was given to the laws of nature, and the JUCA units were designed to best apply those laws. The JUCA is not just an improved version of some existing product. It was designed fresh from the ground up based on technology. In the discussion above, we've seen that air-tightness, secondary combustion and the catalytic were developed to cure the problems of short-lived fires and great variations in heat output. The JUCA solution is along a totally different line that avoids many of the problems of airtight based designs.

By using large diameter unsplit logs (6-10" dia), a fire is obtained that is very long lasting with very constant output. Since we get long burn times and constant output (the original purpose of airtight designs) WITHOUT suffocating the fire, the wood is able to burn very, very completely and cleanly leaving little ash and only minimal unburned gases in the smoke. With so little unburned fuel in the smoke it is unnecessary to have to get secondary combustion or catalytic action to occur. That is only necessary in airtights where the problem of extensive creosote is present.

Since we have a relatively tame, even, long-lasting fire the JUCA design now puts a sophisticated heat exchanger in the smoke path to make sure to capture all the heat possible before the smoke escapes up the chimney. Our computer helped design the structure of the heat exchange system to best apply the laws of aerodynamics, thermodynamics, and other modern technology.

For example, the sloped sides of the free-standing models are at a very specific angle. As the smoke in the firebox leaves the fire it is quite hot and takes up a lot of space. As it rises through our heat exchanger and we extract heat from it, the smoke cools and takes up less space. By having the sides slope in the right angle, the JUCA permits a condition called isobaric equilibrium where air pressures in different parts of the smoke path are the same. This allows remarkably stable and effective heat transfer.

Since we burn the wood very cleanly with little creosote in the smoke, the JUCA heat exchanger can be made very efficient. An airtight cannot safely remove heat after the smoke cools to 400°F because then all that massive creosote in the smoke would condense in the chimney and cause a hazard.

Since a JUCA produces so much LESS creosote IN THE SMOKE, we can extract those extra Btus without massive creosote deposits in the chimney.

The concepts of air-tightness (causes a lot of creosote) and efficient heat exchange (condenses most of the creosote present) are just not safely combinable. JUCAs are different.

Many advanced features are designed into the JUCA products. The woodburner of the future.

The JUCA Home Page is at: juca