The Three Stages of Wood Combustion

Improving fireplace efficiency can be achieved in many ways, such as switching to a fireplace insert. Knowing about the stages of wood combustion can help, too. Wood goes through different stages during the burning process. First, however, there is some prep. You can maximize the BTUs per pound of wood when you practice efficiency, starting with the type of wood you burn.

Prep the Wood

It is impossible to burn wood efficiently if you burn green firewood. When a tree is harvested for firewood, the wood is fairly bursting with moisture. In fact, the moisture content is about 100%, meaning that half of the full weight of the wood is water.
Logs need to dry out in proper storage conditions for a minimum of 6 months up to a year or more to get to the right moisture content for burning. You can use a digital wood moisture meter to make sure the moisture level is about 15% or 20%–and never more than 25%. A wood moisture meter can cost as little as $12.

Prep the Chimney Flue

There may be one more step needed before you get to the stages of wood combustion, and that is to warm up the chimney flue. In icy temperatures, cold air can fill the chimney flue. The cold air needs to be displaced before a fire gets going full tilt. Otherwise, the toxic combustion gases will pour into the home.

The most common practice for warming the flue is to fashion a torch with a newspaper, light it, and carefully hold it up to the damper above the firebox. It may take two or possibly three times to make sure there is a strong chimney draft.

Stages of Wood Combustion

Moisture is Eliminated

When you light a fire, the first thing that happens is that the moisture is removed from the log. The moisture begins evaporating at about 212º F. The wood begins hissing and bubbling. Moisture is eliminated when the temperature of the fire is about 400º F. If this process is prolonged because of high moisture content, a lot more creosote is deposited in the flue lining.
Creosote is highly flammable and increases the risk of a chimney fire. Experts recommend scheduling a chimney cleaning when there is a 1/8”-thick layer of the black, tar-like substance lining the top portion of the flue.

Complete Combustion

Next is the heating stage, and this is when combustion is complete. When you see orange flames, the wood is producing maximum heat. Maintain the fire at this level for optimal warmth and fire efficiency.

The Fire Dies Down

When you stop adding fuel to the fire, the flames will begin to decrease. Heat is no longer produced by the combustion process. Eventually, all that is left is a smoldering fire. Combustion gases increase again during this process.

Heating up and cooling down happens more quickly if you burn softwood. Hardwoods are best to use when you want to produce coals for additional warmth, but the dying-out process takes longer.

Call Chimney Pros in Richmond VA for Creosote Removal

Our CSIA-certified chimney sweeps at Chimney Saver Solutions can help with fireplace efficiency. Routine chimney maintenance is the best way to get the most out of your fireplace. Next, you can benefit from knowing the stages of wood combustion. Call us when you need chimney cleaning, chimney maintenance, a chimney inspection, fireplace insert installation, chimney masonry repair, or any other chimney services. Call 804-440-5000 or fill out our online form today!