Lots of people build fires, but many people don't know how to build good fires. Doing it right is essential for keeping chimneys in good working order. To understand why, it helps to know how wood burns:
In the beginning stages of a fire, the heat of the flames removes water from the wood via evaporation and vaporization. This heat doesn't make the fireplace or room any warmer. It just dries out the wood.
As wood dries out, the temperature begins to rise. When it reaches 500°F, the materials in the wood begin to break down and form volatile gases. These gases contain roughly 50 to 60 percent of the wood's heat value.
Temperatures continue to rise. At approximately 1,100°F, gases will break into flames if enough oxygen is available.
Once combustion takes place, the remaining material burns at temperatures above 1,100°F. As it burns, it leaves ash behind as a by-product.
Starting a Fire
Around the House
Always get your firewood from a trusted source who can tell you when the wood was cut and how it was stored. If you cut it yourself, be sure to give it enough time to dry out before you use it. Store it in a protected area away from water and damp surfaces.
Since wet wood contributes to creosote buildup, it's important to use dry, seasoned wood for your fires. You'll sometimes read that hard wood is better than soft, but moisture content is really more important. That said, hardwoods such as oak, ash, hickory, and juniper burn cleaner than softwoods like cedar, pine, and fir do.
Here's how to build a good fire:
Open the damper completely.
Put about a half-dozen crumpled sheets of paper or softwood kindling in the bottom of the firebox. If possible, use both. Stack the kindling in a pyramid or in a crossed pattern on top of the paper. Spread over the entire bottom for an evenly burning fire.
Place a few small pieces of wood on top of the paper or kindling. Use small, split logs instead of big, unsplit logs. Big logs hamper airflow and cause fires to burn slow and long, resulting in increased gas and tar levels. Stack the wood loosely, leaving enough room between logs to facilitate airflow.
Roll up a handful of sheets of paper, light it, and hold it near the flue opening. This will warm the flue and improve the draft.
Light the wood and paper in the firebox. After it ignites, adding more wood will increase the fire's heat. Add wood carefully at first—you don't want to smother the fire by adding too much.
The woodstove fire in this photo is a perfect example of what not to do. Note the closely stacked large logs, loaded tightly in a dirty stove. You can bet the chimney on this stove is full of creosote.
For more on the anatomy of a fireplace and chimney, see Preventing Chimney Fires.