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-foot 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 per cent when they are freshly cut. The
popular hardwoods have moisture contents of about 45 per cent. Air-dried wood may have a moisture
content of about 15 per cent and kiln-dried wood may have a moisture content of less than 10 per cent
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
productive when three conditions are met: The temperature is between 60
o
F and 90
o
F, the wood’s
moisture content is above 30 per cent, 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 stove wood lengths, and spilt, 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 of 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 per cent, the equilibrium moisture content is about
11 per cent. 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 form 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 per cent 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 to provide excessive draft, thereby decreasing the efficiency on 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.
To Next Page
Loading...
