How to build and maintain a wood fire

Whatever your wood burning system, you can improve its efficiency and reduce air pollution by learning to burn correctly. 

The knowledge and skills needed to operate a wood burning system effectively need to be learned and practiced to get them right. Although it is not brain surgery or rocket science, it is not as simple as it might first appear. So, when you can light a fire with a single match and get a hot, bright fire burning in just a few minutes, you've accomplished something worth knowing and we salute the time and care you've taken. Reach around and pat yourself on the back.

How does wood burn?

The water evaporates: Up to half the weight of a freshly cut log is water. After proper seasoning the water content is reduced to only about 20 per cent. 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 consumed. That is why wet firewood hisses and sizzles and is hard to burn while properly seasoned wood ignites and burns easily.	The wood smokes: As the wood heats up, it starts to smoke. The smoke is a cloud of combustible gases and tar droplets. It will burn if the temperature is high enough and enough combustion air is supplied. When the smoke burns, it produces the bright flames. If the smoke does not burn it will flow into the chimney where it will either condense as creosote or go outside as air pollution. Unburned smoke is a waste because it contains a large part of the total energy in the wood.	The charcoal glows: As the fire progresses and most of the gases and tars have vaporized out of the wood, charcoal remains. Charcoal is almost 100 per cent carbon and burns with a red glow and very little flame or smoke. Charcoal is a good fuel that burns easily and cleanly if it is given enough air. Although charcoal combustion produces almost no smoke, the exhaust can have high concentrations of carbon monoxide, so it must be vented completely to outdoors.

In reality, all three phases of wood combustion occur simultaneously because the wood gases can be flaming and the edges of the pieces can be glowing 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 content quickly and make sure the smoke burns with bright flames before it leaves the firebox.  

A note about the advice offered here

The suggestions offered below are effective for the most common form of wood stove; the front loading, updraft, non-catalytic type. The techniques may or may not be suitable for catalytic stoves, or for cook stoves, furnaces and fireplaces. However, the principles are sound and if you need to use different techniques to get good results in your particular system, that is just part of the variety and charm of wood burning.

Starting a fire

• a newspaper (do not use colored or coated paper); 
• a handful of finely split, dry kindling in a variety of sizes; and 
• seasoned firewood split into a range of piece sizes. 

You can build a conventional fire by starting with paper and putting kindling on it, as described below, or you can build a top-down fire. 

1. Crumple several sheets of newspaper and put them in the firebox. The amount of newspaper you need will depend on the firebox size, and the dryness and fineness of the kindling you are using. The drier and finer the kindling, the less newspaper you need. Many people make the mistake of using too little newspaper. Be generous with the newspaper and you will have more success. 
   
2. Hold the paper down with 10 to 15 pieces of finely split, dry kindling. Softwoods, such as cedar and pine, make good kindling. Ideally, the kindling should be placed on and behind the newspaper so that the combustion air reaches the newspaper fast where you light it. It is also a good idea to add two or three very small pieces of firewood to the kindling load before lighting. 
   
3. Set the air control to fully open, light the newspaper and close but do not latch the door. When the paper is flaming brightly, latch the door. Some appliances have more restrictive air supplies than others, so the door may have to be left ajar for as much as 15 minutes until the chimney is primed and producing strong draft. Since leaving the door open slightly can cause dangerously high temperatures, never leave the stove unattended while starting the fire. 

 The goal when lighting a wood fire is to use only one match and to achieve rapid ignition of the load without fussing or waiting for it to catch. After practicing this procedure a few times, you might be surprised at how quickly you can establish a bright, hot fire. When the flames from the kindling load just begin to subside, add several small pieces of firewood. Try to avoid smothering the fire with the new pieces. Placing the pieces on and behind the burning kindling can help prevent smothering. 

Rekindling a Fire from Charcoal

For most wood-burning appliances, the live coals that remain after the fire has burned down are found at the back of the firebox furthest from the air supply. This is the time to clear excess ash from the firebox. Before disturbing the remaining charcoal, remove a small amount of ash from the front of the firebox. Now rake the live coals forward to just inside the loading door. If only a small amount of charcoal remains, you will have to start with kindling. If you have a good quantity of glowing charcoal to work with, place at least three, and preferably more than five pieces of firewood on and behind the charcoal. Open the air inlets fully and close the door.  

If everything is just right, you should expect instant ignition of the new load. In fact, the bottom pieces should be flaming before you get the door closed. Allow the fire to burn with bright turbulent flames until the wood is charred. This usually takes between 15 and 30 minutes, depending on the size of the pieces and the moisture content of the wood. When the wood is charred, you can reduce the air setting to produce the amount of heat and length of burn you desire. You may want to try reducing the air control setting in two or three stages. The result will be less air pollution because the fire will not have to recover from the single, large reduction in air supply. 

 The most important rule is NEVER LET THE FIRE SMOLDER. As long as there is solid wood in the firebox, there must be flames or the smoke will escape unburned, both reducing efficiency and increasing pollution. With modern appliances, it is possible to achieve a reliable overnight burn while maintaining flaming combustion and having enough charcoal in the morning to rekindle a new load. 

More tips and techniques

A loosely stacked load  Good for short or "flash" fires.	A compact fuel load  Good for extended firing cycles

Fire in cycles: Don't expect perfectly steady heat output from the fire. Wood fires burn best in cycles. A cycle is the time between the ignition of a load from charcoal and the consumption of the load back to a coal bed. Each cycle should provide between four and eight hours of heating, depending on how much wood was used and how much heat is needed. Plan the firing cycles around your household routine. If someone is home to tend the fire, use a short firing cycle. If you must be away from the house during the day, use the extended firing cycle.

The flash fire is a small amount of wood burned quickly. Use it in spring and fall when you just want to take the chill off the house. The flash fire technique eliminates the smoldering fires that are common in spring and fall. To build a flash fire, rake the charcoal towards the air inlets and place several small pieces on and behind it. The pieces should be stacked loosely in a crisscross arrangement. Open the air inlet to produce a hot, bright fire. The air supply can be reduced slightly as the fire progresses, but never enough to extinguish the flames. When only charcoal remains, the air supply can be reduced further to prevent cooling the coal bed. 

The extended fire: To achieve a longer-lasting fire, rake the coals towards the air inlets and use larger pieces of wood placed compactly in the firebox. Placing the pieces close together prevents the heat and flame from penetrating the load and saves the buried pieces for later in the burn cycle. Open the air inlets fully for between 15 to 30 minutes depending on load size and fuel moisture content. When the outer pieces have a thick layer of charcoal, reduce the air control in stages to the desired level. The charcoal layer insulates the rest of the wood and slows down the release of combustible gases. This allows you to turn down the air control and still maintain a clean-burning fire. Use the extended fire technique to achieve an overnight burn or a fire to last the day while you are at work. Do not let the fire smolder. 

 Removing ashes: When you follow the suggestions for raking of the coal bed, you will find that ashes accumulate at the front of the fireball. These ashes can be removed easily before coal bed raking in preparation for loading. Most modern wood-burning appliances work best when a small amount of ash is removed each morning before the first fire of the day is built. 

Look for these signs of good combustion:

• When wood burns it should be flaming until only charcoal remains. If there are no flames, something is wrong 
• If there are firebricks in the firebox, they should be tan in color, never black. 
• Steel or cast iron parts in the firebox should be light to dark brown, never black and shiny. 
• With seasoned wood, correct air settings and proper loading arrangement you should expect instant ignition of a new load of wood — the bottom pieces should be flaming by the time the door is closed. 
• If the appliance has a glass door with air wash, it should be clear. 
• If the appliance has a glass door without air wash, it will be hazy, but should never be totally black. 
• The exhaust coming from the top of the chimney should be clear or white. A plume of blue or gray smoke indicates smoldering, poor combustion, air pollution and probably low system operating temperatures.