Huge JUCA Firebox

Large Logs that burn in a JUCA B-3B JUCAs have always been known for their huge fireboxes. Where competing wood-burners often have 2 or 3 cubic foot fireboxes, a JUCA B-3B has a 9.5 cubic foot firebox! The built-in Model F-9A has a 12.3 cubic foot firebox! (The picture shows an 18 inch long ruler amd some 26" long, 8" diameter logs in a JUCA B-3B.)

This huge firebox allows several benefits:

Of course, it allows you to burn much bigger pieces of wood, pretty much anything you could carry! (An 8" diameter, 24" long hardwood log weighs about 30 pounds.) So convenience is a result.

But there are more important results, as well.

It allows you to put enough wood IN it to be able to produce substantial heat for many hours. Each pound of wood has available about 6,000 Btu of heat in it. A competing 2 cubic foot firebox, can realistically contain about 30 pounds of small pieces of wood. In other words, about 180,000 Btu. If that competing product is 70% efficient, that means about 125,000 Btu of heat for the home. That's it! No more! By setting the draft control, it is possible to gain this heat as 50,000 Btu/hr for 2.5 hours, OR as 12,000 Btu/hr for 10 hours. Either enough to heat much of the house, if you are willing to load it every 2.5 hours, OR enough to heat a single good sized room for a full night!

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We at JUCA have always thought that was foolish. Why not have a much bigger firebox (nearly 5 times as big) and then all the numbers above are 5 times as big, too! There is around 600,000 Btu of heat in the wood for heating the home. By using it at 60,000 Btu/hr, there is a nice constant 10 hours of heat, to heat the WHOLE house, for an ENTIRE night. If you think about it, NO product with a 2 or 3 cubic firebox could realistically do that!

The large firebox allows having the heat exchanger areas substantially above the fire. THIS IS REALLY IMPORTANT! If it was closer, as in many competing products, the (relatively) cool metal surfaces of the exchangers can "chill" the flames themselves and thereby affect the completeness of the burning process. This effect is one of the reasons why many competing products create a lot of creosote and pollution, and why they therefore need catalytic combustors and/or secondary air to try to solve these problems. Since JUCA design allows extremely complete combustion IN THE FLAME TIPS, there is no need to try to "re-process" the smoke later.

Another result of the JUCA's large firebox is that THICK logs can be burned. It turns out that wood (or anything else) can only burn (or oxidize) at its surface, where it can interact with the oxygen in the air. As that surface wood burns and disappears (or falls away), new wood is exposed which can then burn.

Thick pieces of wood therefore burn gradually (and evenly) for a long time. With this fact in mind, a combustion system can be designed (as in the JUCAs) where plenty of oxygen is available around the fire area. As each particle of wood burns, there is plenty of oxygen present to ensure extremely complete combustion. Therefore, VERY high combustion efficiency exists and very little pollution or creosote is created in the smoke. At the same time, the thickness of the wood pieces causes a rather constant AREA of wood pieces to be on fire, therefore making heat PRODUCTION (and output) very constant for a very long time. All the desired characteristics of a perfect wood-burner!

Most competing products have smallish fireboxes. This then requires small, split pieces of wood to be burned. These sized pieces of wood would burn up very quickly in the presence of a lot of air, as they did in the old Potbelly stoves and Franklin stoves. Those (non-air-tight) units burned reasonably cleanly, but created heat for only an hour or so, and too much during that hour! Therefore, nearly all manufacturers (except us!) stayed with the tiny firebox, and turned to limiting the amount of air available to the fire, the so-called Air-Tight design concept. They DID accomplish their goal of longer burn time and more even heat production, but at the cost of rather incomplete burning due to insufficient oxygen present for all the chemical reactions which need to occur in complete combustion. Therefore, they are forced to try to complete these reactions later, either in a catalytic combustor or by adding heated secondary combustion air later. Life is very complicated for designers of such devices, only because the basic premise of Air-Tight operation has such a major flaw. (Interestingly enough, as those products developed a VERY bad reputation for creating a lot of creosote and pollution, one of the approaches that became popular was to convince customers to buy the very smallest air-tight product that might do the job, so that it would generally operate "wide open" and avoid air-tight operation!)

JUCAs NON-Air-Tight design allows such complete combustion in the original flame tips, that our NORMAL operation is better than that when Air-Tight products are operated at their optimum.

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