Burning CoalBeginning in late 1979 the word coal started to become popular with consumers. Rumors that we would run out of wood and those saying that we have an almost inexhaustible supply of coal probably had something to do with it. Most wood-burning stoves suddenly started advertising that they could burn wood and/or coal even though the products had not been changed or improved. Those woodstoves could NOT decently burn either main type of coal! These are some of the great number of misconceptions that have developed around the use of coal.
SUPPLY - The coal that may last us 500 more years took 100,000,000, years to form. After 500 years that will be it! In contrast, hundreds of millions of cords of wood grow every year on earth. The supply continually replenishes itself. It doesn't always grow in the right places, but it does grow!
Getting more specific: Can coal be burned in a JUCA? Well, the answer is generally yes, it is possible, but the word COAL can mean quite a wide variety of burnable materials.
In order to burn Anthracite in any device, the coal should be contained in a rather tall and narrow holder, which should generally be made of cast iron for decent durability. That vertical configuration is important in order to provide a lot of heat to the coal near the top, such that it can start to burn and remain burning.
A Grate to burn Bituminous is very different from that needed to burn Anthracite, generally being wider and not tall. Far lower combustion temperature is necessary than for Anthracite, which makes Soft Coal a far friendlier fuel to use, except for a lot of pollution generally created.
Cannel Coal contains a lot of volatile gases inside which enables the easy lighting and maintaining of a fire. Pollution created is even worse than with Bituminous.
This is material which WOULD HAVE become coal if it had gotten buried deeper and for millions of years, but is an intermediate state of that development. Peat bogs are the preliminary state of eventual coal formation.
In contrast, coal is primarily carbon atoms, so it is essentially all fuel, which makes coal a far more compact form of fuel energy, Anthracite contains the most carbon so it contains around 16,000 Btu/lb, while most Bituminous coals have more assorted other elements in them which reduces their energy content to around 13,000 Btu/lb. These energy contents compare well to hardwoods which generally have around 8,500 Btu/lb energy content. In all cases, each individual mine has its own average energy content of its coal. But in all cases, coal is a far more compact form of fuel than wood is, commonly roughly twice the energy content per pound.
USE IN A WOODSTOVE - As stated in the wood-burning industry trade magazine, Wood 'N' Energy there are no true combination stoves on the market today that will burn wood and both main types of coal equally well. The design characteristics of stoves designed for each are so different that any stove which claims to be a combination must sacrifice burnability and efficiency in one or more of the different fuels. Most wood stoves are not well suited to burning coal at all, and many coal stoves are too small to accept a healty charge of wood. Unfortunately advertisers sometimes ignore these facts in order to sell stoves.
POLLUTION - It is true that coal does not cause the excessive creosote deposits found in air-tight wood burning but there are some pollutants that are worse than from wood burning, such as sulphur dioxide (from most bituminous coal) which chemically combines with water vapor to produce H2SO3, a weak sister to sulphuric acid, and the usual cause of "acid rain".
OTHER CONSIDERATIONS - The shape of a firebox should be suited to the fuel; tall and very narrow for hard coal (anthracite); small, low and wider for soft coal (bituminous); much larger for wood. Anthracite is generally only available in Pennsylvania. Combustion air flows are very critical with coal (especially anthracite), otherwise the fire will go out. Even just loading more coal on a good, strong fire can make it go out. Clinkers are a continual problem with coal. Coal produces 7 to 10 times the ash/clinkers of wood. A very important concern is that large amounts of volatile gas is produced. In an airtight wood-burner this could pose an explosion hazard. Coal burners must not be airtight. (JUCAs ARE NOT AIRTIGHT)
We designed the JUCA's to burn wood. They do an amazingly good job at that. When we submitted them for safety testing to UL standards we requested testing with wood, so that UL Test approval is for wood only.
We like to think that a JUCA will last many, many years using wood. We believe that the lifetime may be shortened if coal (especially high sulfur bitnminous coal) is consistently burned. We don't know how much. In the thousands of units we've built over the last thirty five plus years, we're not aware of any failures yet. A small number of owners have ignored our recommendations and burned primarily coal for up to 5 years now with no problems yet.
Some customers indicate that they intend to use some coal mixed in with wood. In this situation, there should be minimal deleterious effect due to burning coal. You would also likely need a coal grate.
As mentioned above, we don't encourage ALWAYS using coal in a JUCA, but if your going to burn it sometimes, we'll help you do it properly. We do research and testing of ideas on coal. For example, there are some anthracite coal grates sold that would fit inside the B-3B and could be put in a B-3B to burn hard coal.
Finally, a disclaimer. Coal burns at a hotter temperature than wood does. Soft coal often has a substantial sulfur content, that creates a weak acid as a result of being burned. For these reasons (and others), ALL products that are meant to continuously burn coal are made of cast iron and not steel like the JUCA is. The heat exchangers will perform extremely well, so the JUCA will produce a lot of heat. But we will not honor the forever warrantee for units that have regularly been burned with coal.