Preparation Of Wood; Once I Have My Wood At Home, How Do I Prepare It For Burning?; How Much Moisture Is Contained In Wood?; What Causes Wood To Rot? - Newmac WG-100 Installation, Operating And Service Manual

PREPARATION OF WOOD

Once I have my wood at home, how do I prepare it for burning?

The wood must be cut to length to suit the firebox of the stove, furnace, or fireplace in which it is to be
burned. An 8' log may be cut into four, six or eight pieces, depending on the desired length. Splitting the
wood greatly facilitates drying and reduces the wood to a more manageable size.

How much moisture is contained in wood?

Many softwoods have a moisture content in the vicinity of 55 percent when they are freshly cut. The
popular hardwoods have moisture contents of about 45 percent. Air dried wood has a moisture content of
about 15 percent and kiln dried wood may have a moisture content of less than 10 percent when it is fresh
from the kiln.

What causes wood to rot?

When wood is cut, it is very susceptible to the growth of fungi, which converts the wood to water, carbon
dioxide, and heat, just as does a fire. This rotting decreases the wood's energy. The fungi are most
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productive when three conditions are met: the temperature is between 60 F and 90 F, the wood's
moisture content is above 30 percent, and ample oxygen is available. Thus, wood does not rot appreciably
when it is dry, in the winter, or when it is submerged in the water, but it should not be allowed to lie on the
ground during the summer.
How can this rotting be prevented?
When the wood has been cut into stovewood lengths, and split, it should be piled outside during the months
of June, July, and August. Two poles should be placed on the ground to serve as rails to keep the firewood
off the moist ground and the wood should be piled up in such a way that it is well exposed to the sun and
the wind. The moisture content of the wood will drop until it reaches equilibrium with the ambient weather
conditions. When the relative humidity is 60 percent, the equilibrium moisture content is about 11 percent.
When the wood has reached this equilibrium moisture content, it is said to be "air dried." Around mid
August, it should be placed under cover so that it will not reabsorb moisture from the rain and snow before it
is used.
Why this concern about allowing the wood to dry?
Green or wet wood is undesirable for several reasons. Green or wet wood tends to mildew and rot which
causes a significant reduction in the thermal value. When green or wet wood is burned, it may take 20 to
25 percent of the thermal value of the wood heat to evaporate and drive off the moisture, which is
contained. Green wood does not burn easily and, in order to keep the fire burning, it is often necessary to
add a lot of fuel and provide excessive draft, thereby decreasing the efficiency of the unit. The excess air
needed for combustion must be heated and it escapes up the chimney wasting heat that should be used to
heat the house.
What is creosote?
Wood smoke almost always contains some unburned gases and a fog of unburned tar-like liquids. Some of
these materials will condense on the inside of the chimney, just as steam condenses on any cold surface.
This condensation is a black, tacky, fluid when first formed. When it dries, it is flaky and shiny. Creosote
has approximately the same thermal value as fuel oil. Not only does it reduce the effective size of the
chimney, but an accumulation of this material constitutes a serious fire hazard.
Does green wood cause creosote?
Yes. Indirectly, green wood does cause creosote. The exhaust gases cool as they rise up the chimney. If
the temperature falls below the dew point, any moisture contained in these gases will condense on the
inside of the chimney, absorb the various products of incomplete combustion and form creosote. When
green wood is burned, the exhaust gases carry a high moisture content in addition, because of the heat
required for evaporation, these gases are cooler and more likely to condense than would be the case with
dry wood.
Charcoal may be formed more readily if the unit is overcharged, particularly in milder weather. With
overcharging (too much wood in unit) the draft fan will be off a greater percentage of time, coals will be
formed which will become covered with ash and in turn will smother the coals to form charcoal. Any coals
in the furnace should be stirred before more wood is added to it.
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