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Using the Best Firewood for Home Heating

How to Burn Wood to Produce Quality Heat


Pieces of wood
Mim'sMadMoments/Moment Open/Getty Images

Finding Firewood:

If you are looking for firewood to cut, you need a wood source that is relatively close to your storage area and easily accessible by your vehicle. If you have a place to store and season the cut wood, inexpensive wood can be found nearly anywhere trees are being removed because of storms, right-of-way clearing, or logging. Places to look for wood would be sawmill yards, national forests, logging and arboricultural operations and your own property. An old saying, "the best firewood is free firewood" has a lot of merit if you have the desire and equipment to process it and a place to put it.

Many urban firewood users purchase processed wood because of its convenience, availability and deliver-ability. It takes a lot less room to store the wood and is usually processed to fit the fireplace or stove. Processed firewood comes at a premium cost which is associated with preparation, handling and transportation. You need to acquaint yourself with the value of firewood in your area and pay a fair price. You can find plenty of great dealers online and in the phone book.

Easiest Wood to Split:

Some tree species are a real pain to work with and should be avoided by the do-it-yourself processor. Elm can be tough and difficult to split while ash splits easily. Splitting enables the wood to dry out faster and reduces the size of the sticks to stove or fireplace size. Some wood has to be split to use in a stove.

Various woods have different splitting characteristics which are important to consider. Some woods split with little effort while others can be tough, stringy, and difficult to split. Tree species to avoid because of splitting difficulties are elm, sycamore and gum. Tree species especially easy to split are most conifers, oaks, ash and hard maple.

Woods with interlocking grain like elm, gum or sycamore are to be avoided and are difficult to split even with a mechanical log splitter. One rule of thumb should also be remembered - green wood will split more easily than dry wood. Also, softwoods will generally split more easily than hardwoods.

How Wood Burns:

Every species of wood provides different quantities (BTUs) of usable heat when burned and I will get into that later. A good way to look at usable heat from wood is by looking at the burning stages of wood upon ignition. Heating efficiency of firewood depends on how that wood progresses through the three stages of burning.

In the first stage, wood is heated to the point where moisture within the wood cells is driven off and the cells are drying out. As the wood is losing moisture, it is chemically changing into charcoal - which is famous for its volatile gases and liquids. Stopping the process at this point is where the charcoal industry packages their products.

The second stage is where actual flames burn off the volatile gases and volatile liquids to the point where charcoal has lost most of these volatile fuels. Much of the energy of wood fuel is lost during this stage and where premium wood burning systems can improve their efficiency.

Finally, the third stage occurs when the charcoal burns and can be seen when the embers glow. This is called "coaling". At this point, heat is radiated from the burning bed of coals. Different species of wood burn and expend energy differently throughout these three stages.

The point to be made here is that a good firewood species should be dry, should burn through the second stage without sparks with a minimum of smoke production, and spends a long time burning in the third "coaling" phase.

Wood That Burns Best:

The heating potential of wood depends upon the increased density of that wood. A wood's density is genetically determined by the tree species. Dense or heavy wood contains higher heating values, in British thermal unit’s per unit volume, than lighter woods. A British thermal unit (BTU) measures the amount of heat required to raise the temperature of one pound of water one degree Fahrenheit.

Most of us don't realize that air dried wood will produce about 7,000 BTU’s per pound regardless of the species - all wood burns with the same value. The catch 22 here is in the density variation between different species which can be significant.

As an example - one unit of heavy oak wood will produce roughly as much heat as two units of cottonwood when measuring BTU output. So lighter woods like cottonwood and willow will produce the same heat per pound as the heavier oak and hickory woods. This means that a greater volume of cottonwood is needed than oak to produce the same amount of heat.

Other things to consider is that some species of wood start easier than others but give off more smoke and more sparks than others. Easy starting wood is not necessarily the best wood to use for heating. Remember that different species of wood will last longer and have better coaling qualities than others. It is important to consider these factors when selecting firewood.

The Needle and the Leaf Debate:

So now we address the issue of burning needled conifers and softer wood species. Harder wood species that are very dense, and typically called hardwoods, are the firewood of choice in North America. The problem with this is not everyone has access to wood in the Eastern hardwood forest. Conifers and softwoods have served well in those regions with limited hardwoods but the limitations are known and overcome with proper preparation and appropriate wood burning systems.

On the positive side, conifers are easier to ignite because they are resinous. Still, these softwoods tend to burn rapidly with a high, hot flame and burn out quickly, requiring frequent attention. Finding a wood heating unit that can store this quick heat and distribute it through time is critical.

Red cedar and other trees with high-resin will often hold "moisture pockets" which can be both irritating and dangerous without the proper burning hardware. These trapped gases will cause a pop when heated sending out sparks. This can present a significant fire risk, especially when burned in open fireplaces without screens.

Hardwoods will burn longer but less vigorously when compared to softwoods. The wood is harder to start and conifers are often used to kindle the wood burning process. The reason hardwoods make the best fuel is because they tend to produce more coals, a process called "coaling", that last longer than softwoods. Well seasoned oak makes an excellent fuel because it produces a uniformly short flame and provides heat preserving coals.

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