Boiling off the water - Up to half the weight of a freshly cut log is water. After proper seasoning, the water content is reduced to about 20 percent. As the wood is heated in the firebox, this water boils off, consuming heat energy in the process. The wetter the wood, the more heat energy is used to boil the water. That is why wet firewood hisses and sizzles and is hard to burn, while seasoned wood ignites and burns easily.

The emission of smoke - As the wood heats up and passes the boiling point of water, it starts to smoke. The smoke is the visible result of the solid wood decomposing as it vaporizes into a cloud of combustible gases and tars. If the temperature is high enough and oxygen is present, the smoke will burn. When it does, it produces the bright flames that are characteristic of wood combustion. If the smoke doesn't burn in the firebox, it exits the furnace into the flue pipe and chimney. Here it either condenses - forming creosote deposits - or is expelled as air pollution. Unburned smoke also represents a less efficient furnace because smoke contains much of the wood's total energy.

 
 

The charcoal phase - After the water has boiled off and most of the gases and tars have vaporized out of the wood, charcoal remains. Charcoal is almost 100-percent carbon. It burns with a red glow and some flame or smoke when enough oxygen is present. Charcoal is a good fuel that burns easily. However, burning charcoal often produces carbon monoxide, an extremely deadly colorless, odourless gas.

In reality, all three phases of wood combustion usually occur at the same time. The wood gases can flame and the edges of the pieces can glow red as charcoal burns, while water in the core of the piece is still evaporating. The challenge in burning wood effectively is to boil off the water in the wood quickly, while making sure the smoke burns with bright flames before it leaves the firebox.

 
 

What To Burn?

Always Burn

• Clean dry wood
• Properly seasoned split wood
• A mix of hard and soft wood, where possible, depending on what's available in your region.

  
  Never Burn

• Wet or green wood
• Houshold garbage such as pastic or cardboard.
• Painted or stained wood
• Pressure treated wood
• Particle board or plywood
• Ocean driftwood
• Glossy magazines
• Any materials prohibited by local by-laws

Preparing Your Firewood Supply

Several tree species are used for firewood, and those you choose will affect your wood-burning system. Trees that have the hardest wood and the most energy per cord, while the softest have the least energy per cord. Regardless of where you live and what species are available, try to mix the load as much as possible. This will ensure that you do not use too much wood of one species as your primary fuel source.

Firewood should be split and stacked under cover in the early spring to be ready for burning in the fall. After drying in the warm summer winds and sun, the wood will have a moisture content of about 20%. A piece of dry firewood has large cracks or checks in the end grain. Look for these when judging the quality of firewood. Hardwoods and softwoods are chemically similar - the difference is density. Hardwoods being more dense, producing a longer lasting fire. However people living in Canada's north where hardwoods do not grow, are able to heat their homes quite effectively with softwoods. Whether hardwood or softwood, your fuel should be clean, untreated and unpainted wood.

The Firewood Cord

Firewood is measured in cords. A full cord measures 4 ft. x 8 ft. x 4 ft. Many firewood dealers also sell partial cords called face or stove cords which measure 16inches x 8 ft. x 4 ft.

Starting Or Rekindling The Fire

When starting a fire, use plenty of crumpled newspaper and kindling. As a guide, put in up to 10 full sheets of crumpled newspaper and hold it down with at least 10 pieces of finely split dry kindling. In order to get a good fire started, build the fire at the front of the furnace where the combustion air enters the furnace. When rekindling, rake the live coals towards the combustion air inlet of the firebox. Make a compact pile of charcoal and place the kindling and small pieces of wood on and behind it. When the controls open the air damper the fire will re-start.